A couple of shots of the Thursday Physical Geology lab section, out hiking on the Billy Goat Trail:



A great group of students.... Photos courtesy of Judi Scharfman.

Labels: field trips, maryland, nova, piedmont, teaching

Got this yesterday via the NAGT newsletter:

REU Project in Yellowstone National Park

Greetings from Montana! We would appreciate your help in advertising to your students an NSF/GEO site project we will be running this summer on Evolution of the Precambrian Rocks of Yellowstone National Park (Dave Mogk, Paul Mueller, Darrell Henry, and Dave Foster PIs). Please visit the project website for further details. This project will be a comprehensive research experience that will include:

• Field mapping and sampling in Yellowstone National Park to contribute to a new geologic map of the basement rocks of YNP; students will work in small groups in the context of the larger project to define and address specific research topics in their area of interest; Dates: June 27-July 25, 2010;
• Direct experience in modern analytical studies including sample preparation, training on modern instrumentation petrologic, geochemical and geochronological; visits to analytical labs will be scheduled for fall semester 2010, and
• Presentation of research results, by submitting an abstract for a poster presentation at the Rocky Mountain Section meeting of the Geological Society of America, and participating in a group reunion meeting to contribute to a peer-reviewed journal article. Dates: Spring 2011, to be determined; Logan, Utah.

We are looking for a group of students (12) with diverse interests in geology to contribute to the research group. To unravel the geologic history of these Archean rocks, our research team will need students with interests in igneous and metamorphic petrology, sedimentology, geochemistry, geochronology and structural geology and tectonics. Students who have taken most of their geology “core” courses and have had a field camp (or other field experience) will be preferred. This experience will provide a great foundation for follow-on senior thesis/research projects at their home institutions. Please note that this will be a true back country experience in Yellowstone National Park, so students need to know that the daily routine will be physically challenging in this rugged terrain.

How to Apply:
Please send: a) Your letter of interest, stating what you hope to learn, what you can offer to this project, b) two letters of support from faculty or work supervisors, and c) your academic transcript . These materials can be submitted to (e-mail or mail):
David Mogk mogk@montana.edu
Dept of Earth Sciences (406) 994 6916
Montana State University
Bozeman, MT 59717

The deadline for applications is: January 30, 2010

Thanks in advance, and please, encourage your best, field-oriented students to apply!

Labels: field trips, maps, national parks, teaching, wyoming, yellowstone

On my Historical Geology field trip to the Massanutten Synclinorium, we observed oolites (ooids) in Cambrian-aged limestones deposited in the Sauk Sea. Like these:

Now the students have submitted their papers on that field trip. Grading the papers, I realized that some of my students were confusing how ~spherical oolites form (through chemical deposition on moving grains) with the perhaps more intuitive process by which clastic grains get rounded with transport. I made up this diagram to illustrate the difference between the two processes:



On the left, you see marine deposition in warm water becoming more concentrated in its load of dissolved ions as evaporation removes water (but not ions). Accordingly, chemical precipitation of calcite begins. Little grains on the bottom get a layer of calcite deposited over them. These grains are within reach of the wave base, so they get rolled in one direction, then rolled back again. As they oscillate back and forth, they expose "both their back and their belly" to the precipitating calcite, so they get concentric layers deposited: oldest in the middle, youngest on top. Like a gobstopper! Or a hailstone. They literally grow more spherical over time.

On the other hand, the right side of the diagram shows a chunk of rock, broken off from its source area, and tumbling downstream. As it travels, the sharp corners are most susceptible to being snapped off or abraded away, meaning that as it loses volume, it takes on a more and more rounded shape. This is physical weathering at work, not chemical precipitation. Note that even if it's very well rounded, that doesn't mean that it's necessarily spherical.

Labels: art, cambrian, field trips, limestone, primary structures, sediment, teaching, weathering

The past week has been one of the more frustrating weeks for me at my workplace. It's been a litany of bureaucracy and incompetence, and my faith in (some of) my coworkers has dropped precipitously. I had to send twenty e-mails to get the college Catalog updated with my correct position title and educational information. Yesterday, I saw a delivery man pushing a cart, opening the door with the handicap access motor (wasting the building's heat), and his special cargo that he needed the cart for was... a lone letter measuring 8.5" by 11"! The particular incident that's raised my ire this morning is the following:

We run these one-credit Field Studies in Geology courses, GOL 135. The Spring 2010 Schedule of Classes lists the different sections of GOL 135 inconsistently across NOVA's different campuses. Here's a comparison between the Alexandria and Annandale campuses' listings. Guess which campus is going to have its sections fill up with students based on this? Guess which campus is probably going to have to cancel classes due to insufficient enrollment? (Guess which campus I work at?)

Someone has screwed up here, and I'm not pleased about it. Grrr.

Labels: field trips, nova

Yesterday, we had a joint NOVA-University of Pittsburgh at Johnstown field trip to Shenandoah National Park. It was a great day of examining new rock outcrops and old treasured favorites. UPJ is responsible for one of the only departmental student-centered geology blogs that I am aware of, Mountain Cat Geology. A couple of weeks ago, igneous and metamorphic petrology professor Elli Goecke contacted me about local rock options, and I invited her crew to team up with the NOVA GOL 135 field course to check out Shenandoah. [Geoblogger small world: Elli studyed under Kim Hannula in Vermont!]

Together, the sixteen of us checked out evidence for the two Wilson Cycles recorded in the rocks of Virginia's Blue Ridge province, and had a pleasant time hiking around and enjoying unparalleled fine weather. Unfortunately, November means the days are short, and we had the sun set on us before we got to the final stop (at Signal Knob Overlook). We took a group photo there: see if you can spot who's a NOVA person and who's a UPJ person...


The annotated version, to show who's who:


Thanks for a great day in the field, everyone!

Labels: blogs, blue ridge, field trips, national parks, nova, pennsylvania, shenandoah, virginia

I've just submitted a list of the classes I intend to teach for summer 2010. Here they are on NOVA Geoblog, before you can access them in the official Schedule of Classes...

GOL 135 (070N) The Bedrock Geology of Washington, DC. HYBRID COURSE: pre-trip reading, field study and post-trip report. One-day field trip Saturday, June 12. Rain date: Sunday, June 13. Important pre-trip logistical information and preparatory readings located online. This trip will focus on the land upon which the capital city is built, including exposures in Rock Creek Park, Georgetown, and Adams-Morgan. Includes discussion of oceanic sediments, the Rock Creek shear zone, igneous rocks emplaced during Appalachian mountain-building, Cretaceous river gravels, dinosaur bones and recent faulting. Students will be evaluated with a field trip report which will be completed after the trip itself. NOTE: This trip involves moderately strenuous hiking on forest trails. Meet in back of the CT building at 9:00 a.m.; Return by 7:00 p.m. For information about meeting time/place or other questions call (703) 323-3276 or email cbentley@nvcc.edu
HYBRID course
Additional info online

GOL 295 (4 credits) Regional Field Geology of the Northern Rocky Mountains: July 10 to July 25, 2009. Pre-trip meetings Wed. June 9 and Wed. June 23, 6:30pm, in CS 217. Western Montana and Wyoming showcase tectonic, sedimentary, geomorphic, and volcanic features which provide world-class examples of geologic processes. Students in this course will complete field studies of locations in Yellowstone and Glacier National Parks, as well as several other field sites. The course will involve VERY STRENUOUS outdoor physical activity: Students are expected to hike several miles at high elevations in rough mountainous terrain in order to accomplish course objectives. Airfare, lodging, and transportation are covered in the approx. $1400 course fee (does NOT include tuition). For up-to-date information and a complete itinerary, see the course website or contact the instructor at cbentley@nvcc.edu or (703) 323-3276.
Extra fee
Instructor permission required
Additional info online

GOL 299 (071N) (2 credits) Snowball Earth. June 14-19, 2009. HYBRID COURSE: pre-course reading, lab, field study and post-course report. An episode of glaciation 700 million years ago, dubbed Snowball Earth, may have provided for the evolution of multicellular life. The Snowball Earth glaciations stretch our conception of the limits of climate change: the ice apparently reached from the Earth's poles to its equator! Scientists infer that the runaway freezing event was only ended due to volcano-induced global warming. This course examines the geological, chemical, and biological evidence for Snowball Earth, and includes a field trip to local "Snowball" deposits. Course meets four times: three evening sessions (6pm-9pm) in CS 217 and all day on a Saturday (9am-5pm). The schedule is: Monday June 14 (lecture), Wednesday June 16 (lab), Friday June 18 (discussion), and Saturday June 19 (field trip). For further information call (703) 323-3276 or email cbentley@nvcc.edu or go to the course website.
HYBRID course
Additional info online

Anyone in the Northern Virginia area who's interested in any of these classes, drop me a line!

Labels: dc, field trips, geology, montana, nova, snowball earth, teaching

My colleague Ken Rasmussen and I were among ten faculty featured in a video that NOVA-Annandale Provost Barbara Saperstone commissioned to brag to the NOVA Board about all the cool stuff going on at her campus. If you're interested in watching the video (~17 minutes), it can be downloaded here. If you're only interested in the geology portion, fast-forward to 14:57 or so. (They saved the best for last.) Enjoy!

Labels: field trips, movies, nova, teaching

Rockies co-instructor Pete Berquist was quoted in a nice little article appearing recently in Thomas Nelson Community College's internal newsletter. Here it is.

Labels: field trips, montana, nova, teaching

Here's some images from my first post-master's-post-master's graduate class: "Bahama Montana," Dave Lageson's one-credit examination of carbonate sedimentology with a particular focus on some interesting features in the Bridger Range: Waulsortian-type bioherms. This field trip was on my fourth day in Montana this summer, following a two-hour lecture the previous evening. Unfortunately, the road to Fairy Lake still wasn't totally open, which meant that we had to add an additional three miles each way to our hike, which meant we didn't get to examine the bioherms themselves at close range. Oh well; next year perhaps...

The class hiking up to the summit of Sacagawea Peak:

(The green stripe on the left/west may look familiar from the satellite image I shared yesterday.)

Sacagawea Cirque, not looking especially "Death Cirque"-like* today:


The view south from Sacagawea Peak:


The class, looking east from the summit:


The elusive Waulsortian bioherms, off in the un-logistically-feasible middle distance:

...Interesting that they weather out in high relief, eh?

Dave instructs:






Some cool Columella stromatolites that I hadn't noticed on previous trips up Sacagawea:


More Columella stromatolites:


The class was a good example of how field trips have to be modified to fit local conditions. It was a bummer the road closure added six miles to our hike, but we were able to scour the talus slopes in Sacagawea Cirque for Mississippian fossils like crinoids, brachiopods, corals, and bryozoans. I got some sweet samples of fenestrate bryozoans, but saw none of the spectacular rugose corals that I collected on my first visit to this cirque 2 years earlier.

_________________________________
* The "Death Cirque" moniker is one applied by my NOVA Rockies students the following week, for reasons I shall reveal in due time...

Labels: field trips, fossils, limestone, mississippian, montana, stromatolites

Labels: art, dc, field trips, geology, nova

Two examples of plumose structure, beautifully expressed in a small boulder of the Helena Formation (Mesoproterozoic limestone from the Belt Supergroup) in Glacier National Park, Montana. Photo by Bob L'Hommedieu.

Labels: field trips, limestone, montana, national parks, proterozoic, structure

Hey there everyone,

Sorry for the unconformity in my posting. Time has been passing, and events have been occurring, even if they haven't been recorded here. I'll try and compensate for that over the coming month.

My Rockies field trip went well. I think everyone had a good time, and there was clamoring for a similar regional field course next summer. I have some ideas for what that might look like, and undoubtedly I'll start planning that in the coming months. In the meantime, though, it's summer in DC, and time for a bit of R&R.

-CB

Labels: dc, field trips, montana

Two cool courses taught by my esteemed colleagues... If you're local and love rocks, you should enroll in both of these!

Birth of the Appalachians. GOL 135-003A. Saturday, June 20. A one-credit field course to investigate the paleogeography of Virginia, prior to the initial uplift associated with the Appalchian Orogeny. We will be specifically looking at rock outcrops representing the pre- and post-uplift topography and environments, based on evidence in the present Shenandoah Valley of Virginia. Light hiking and roadside geology. Contact Victor Zabielski for more information: vzabielski@nvcc.edu

Mid-Atlantic Field Geology (for educators and interested others). GOL 295-050N. A coherent series of one-day regional field trips, plus on/off-campus lectures and labs on Thursdays (2 - 8:20 PM) during second summer session (also two Saturdays: 7/18, and 8/1). This is an introductory-level, four-credit lecture/lab/field hybrid course, tailored to educators and interested others. It considers local outcroppings of the mid-Atlantic Coastal Plain, Piedmont, Blue Ridge, and Valley and Ridge, as natural classrooms for the demonstration of geologic principles, the study of earth history, and the collection of demonstrative hand-samples. Specific meeting places/times and preparation will be sent via student VCCS email addresses & Blackboard. Class # 12594. If more information is necessary, feel free to email: krasmussen@nvcc.edu

Labels: field trips, geology, nova, virginia

Yesterday, I took a little tour out along old Route 55 through West Virginia, the road that was replaced by new Route 55, also a source of cool outcrops. My host was Maitland S., a retired gentleman who occasionally takes geology classes at NOVA. We saw a bunch of cool stuff out there, and I'll share it all with you.

First, check out these lovely pyrolusite dendrites:





Pyrolusite is MnO2, and often grows in these beautiful branching forms. It's totally an inorganic process, but the visual similarity to botanical branching makes pyrolusite dendrites a particularly insidious form of pseudofossil. Here, it's growing on limestone, presumably the Devonian Helderberg Group -- though I'll have to check on that to be sure.

Labels: field trips, fossils, minerals, valley and ridge

On Saturday's Bedrock Geology of Washington, DC class, my students and I had the good fortune to stumble upon two geologists out doing field work: Tony Fleming, lead author of the geologic map of the Washington West quadrangle, and Steve Self, senior volcanologist with the Nuclear Regulatory Commission. They were out looking at the Sykesville Formation at Chain Bridge Flats, assessing a potential reinterpretation of the unit.

Fortunately, they were willing to take a little time and discuss their findings with the students. Here's a couple shots of Steve talking to the group:




I joined Steve and Tony in the field yesterday (Monday) too, looking at some outcrops on the other side of the river, and trying to make sense of them. Fun stuff! More on that at a later date...

Labels: dc, field trips, geologists, geology, igneous, metamorphism, nova, piedmont, sediment, volcano

And now, a few images from April's Environmental Geology class field trip. We made three stops: (1) a large coal-fired power plant in Maryland, (2) Westmoreland State Park in Virginia to look at coastal erosion, and (3) Prince William Forest Park in Virginia to look at pyrite emplacement and acid mine drainage.

Here's one of the bluffs on the Potomac River at Westmoreland:

Note the recent pile of breakdown in the middle of the bluff where all the water seepage is, and also the orange trail as soil from the uppermost bluff has marked another mass wasting event's passage down to the river.

These are Miocene-aged sedimentary layers known as the Calvert Formation, part of the Coastal Plain. In places, the gray clay has been altered along fracture surfaces, as shown by these orange stripes criss-crossing one another. My toes for scale:


The students spent some time searching for fossils: this is an area where lots of shark teeth are found. We didn't have much luck, but after a long cold winter, it was nice to be standing in the warm sunshine and water:


At Prince William Forest Park, we hiked down to the Cabin Branch Pyrite Mine to look at the massive denudation there due to acid mine drainage, and we also spent some time poking around for treasures, in this case chunks of pyrite:


We had better luck than at Westmoreland...




...But of course we were in a national park at Prince William, so we left the pyrite where we found it. (Westmoreland, in contrast, allows you to keep any fossils you find in loose sediment: that figures, eh?)

I'd like to say that the group of students I had in Environmental Geology this past semester was terrific, one of the best groups I've worked with in a long time. Maybe it was because the class was discussion-focused, or maybe it was the cookies we ate every Tuesday night, but it was a great experience for me, and I'm looking forward to teaching the course again. Thanks, everyone, for making it so much fun!

Labels: coastal plain, environmental, field trips, maryland, miocene, nova, ore, piedmont, virginia

Last Saturday was my Field Studies in Geology trip to Shenandoah National Park. Here's a few shots from the day's geologizing...

Garnets in the Pedlar Formation granite gneiss, oldest rock in the park at ~1.1 Ga.


Meta-basalt columns of the Catoctin Formation (photo by Mathina Calliope):


At the end of the trip, I have the students order a series of strips of paper with different geologic events in the park's long geologic history. They have to figure out the proper order based on what they learned that day:





Lastly, a group photo overlooking the Browntown Valley:

Labels: field trips, metamorphism, minerals, national parks, nova, shenandoah, teaching

These videos were shot by NOVA's videoman extraordinaire Richard Attix, who helped me immensely this morning by splicing together these movies for use in my MSSE capstone presentation at the end of next month. Enjoy!

Teaching on the Billy Goat Trail (a blend of instructor-focused lecture and student-focused exploration):

Hiking on the Billy Goat Trail:


End-of-trip activity - "Ordering Geologic Events":

Labels: field trips, nova, piedmont, teaching

A reader of NOVA Geoblog forwarded me an announcement for a geology/education position at UNC-Chapel Hill, which led me to check out the rest of the UNC Geological Sciences website. (No, I'm not applying for the job -- quite happy where I am!)

I cited an important paper* by Allen Glazner in my geology master's thesis, which led me to poke around the author's website a bit. He has a nice collection of photos, including field work in the Sierra Nevada (and elsewhere).

One of my favorites is this awesome (and funny) shot of a shear zone. Check out the kinematics on that sucker! It's "textbook"!

Another is this mouthwatering fold.

There are also some great aerial shots featured. This series of the Deep Creek playa reminded me of a very cold night I spent camping in the Deep Springs Basin, then hiking out on the playa and finding a dead bat that had been mummified in the salt. Nice memories...

Anyhow, enjoy the whole series -- a pleasant way to while away fifteen minutes!

___________________________________________________________________

* The article I cited was a really interesting one:

Glazner AF, Bartley JM, Coleman DS, Gray W, Taylor RZ (2004) "Are plutons assembled over millions of years by amalgamation from small magma chambers?" GSA Today: Vol. 14, No. 4 pp. 4-11.

It posits that igneous pluton emplacement is really drawn out, for instance consider the case of the Half Dome Granodiorite, which took ~4 million years to crystallize:

Figure 5 from the paper. The caption reads: "Summary of geochronologic data for the Tuolumne Intrusive Suite, modified from Coleman et al. (2004). Ages are from concordant U-Pb zircon data. Bar height is equal to +/- 2-sigma error and bar color is keyed to rock unit color on inset map. Ages for units are arranged in sequence from outermost to innermost (Kse-Sentinel Granodiorite; Kga-Kkc-tonalite of Glen Aulin-Kuna Crest Granodiorite; Khd-Half Dome Granodiorite; Kcp-Cathedral Peak Granodiorite; Kjg-Johnson Granite porphyry). Horizontal scale is not linear distance, but places samples according to the fractional distance from outer to inner contact of individual units (see Coleman et al. [2004] for a complete discussion)."

I recommend reading the whole paper, especially if the details of pluton emplacement interest you.

Labels: california, field trips, granite, north carolina, plutons

Hey there Northern Virginia-area readers,

Our readers in Kansas, California, Colorado, London, India, & Australia* can't do what you can do.

Only YOU can sign up for NOVA summer field geology courses.

Check them out. See you out there in the real world.

Sincerely,

Callan

* = representative sample only, chosen for geographic diversity. No slight intended for the many other readers in equally far-flung, equally worthy locations.

Labels: field trips, nova, teaching

Whew!

Sorry I haven't posted much here in the past week. I've been swamped.

The good news is that my biggest task is now off my plate (just turned in the first draft of my MSSE capstone to my advisor), and that means I've got some spare attention left for the blog.

I thought I would take the opportunity to share some images from this past weekend's NAGT (National Association of Geoscience Teachers) Eastern Section conference, held at the NOVA Loudoun campus. On Saturday, I led a version of my "Bedrock Geology of Washington, DC" trip for a group of eight conference attendees.

All these photos are from Randy Newcomer, Director of Training and Services for Complete Safety Solutions of Lititz, Pennsylvania, and are posted with his permission... and my annotations!















If you're interested in seeing (most of) these rocks, join next Sunday's Walkingtown, DC tour!

Labels: conferences, dc, field trips, meetings, msse, nova, piedmont

Here's some cool field trips being offered by the Virginia Museum of Natural History. Not particularly cheap, though.

Labels: field trips, fossils, museums, virginia

I just found out about the Appalachian Tectonics Study Group. They run a fun-looking weekender field trip each spring on topics of current research in Appalachian tectonics. I was not able to attend this year's event in the central Blue Ridge (due to the UMD petrology trip), but maybe I'll get to next year's event.

Labels: appalachians, field trips, mountains, plate tectonics

When I visited the exposures along newly-minted New Route 55 in West Virginia in March, I was so impressed, I decided to bring my structural geology students there on our trip. Now, after two stops in the Blue Ridge and a late afternoon anticlinorama, we woke, broke camp, and ate some great eggs and sausage (mine were swimming in coffee due to an accident with the French Press, but hey -- it all goes the same place, right Ben?) and set off to the west.

Hanging Rock Anticline roadcut:


Hanging Rock Anticline as viewed from the valley of the Lost River, where Old Route 55 wends and winds:


Ben, Dave, and Joe on the berm (note the thrust fault above their heads):


Plenty of primary structures to be seen here, too, like these trace fossils:


A hand-sample of trace-fossils (Arthrophycus, I think):


...or this beauty:


Small reverse fault with an offset of ~1 meter:


Here's a fossil (??) that I don't understand and cannot identify. I saw four of these out there. Can anyone (Tom, ReBecca?) help me identify this sucker and understand how it formed?










We moved on down the road a bit, to this lovely monocline (Jim & Jay for scale):


John, Karine, & Ryan take a closer look at primary and secondary structures in these strata:


Lovely flute casts:


Plumose structure #1:


Plumose structure #2:


Paleo-river channels incised into these strata (at the time of their deposition):


Reduction "halo" around a carbonaceous plant fragment fossil:


Ripple marks:


More plant fossils (these were the largest I saw):


Lots of carbon films of shredded up plant chunks:


Ball & pillow / flame structures:


Ditto, and note the graded bedding in the upper sandstone layer, too:


Great trip, everyone! Thanks!

Labels: field trips, fossils, primary structures, sediment, structure, teaching, valley and ridge, west virginia

After the Garth Run high-strain zone and a night hanging out by the campfire at Heavenly Acres with the William and Mary Structural Geology class, the second stop on our Structural Geology trip was in Shenandoah National Park, looking at the deformed meta-basalt columns on the Limberlost Trail. Longtime readers of the blog have seen these unique (in my experience) columns before, in a post from last May.

This is an outcrop of the Catoctin Formation, a series of (mainly) basaltic lava flows that erupted sometime older than 565 Ma (only the youngest, rhyolitic layers have been dated, and evidence suggested that significant amounts of time may have passed between the eruption of each stratum of basalt deeper down in the stratigraphic stack). As the lava cooled, it developed cooling fractures that formed perpendicular to the isotherms. These fractures likely initiated at the top and the bottom of the flow, and propagated towards the middle over time.

Later, during Alleghenian mountain-building (~300 Ma to ~250 Ma, roughly), the rocks were subjected to greenschist-facies metamorphism, and were deformed. The basalt's consituent minerals re-equilibrated and reacted to become other minerals, most notably chlorite and epidote (both of which are green).

Here's John and Joe checking out the columns:


Exquisite! Even arrest lines on the side of each column are preserved. In an undeformed basalt column, these arrest lines would be perpendicular to the column edge. Here, they have a pronounced angular relationship, indicating the shearing of the overall column:


Bobby measures the angular shear along the length of the column:




Goofball professor poses with column:


Jay plays the column like an electric guitar:


We found some nice plumose structure too:


Finally, we evaluated the concentric rings of minerals filling amygdules (vesicles that had been infilled with mineral deposits after lithification) in an attempt to determine whether they could be used as strain markers, or whether they may have attained their ellipsoidal shapes due to stretching of the bubbles in the originial lava (i.e. like this) and then been infilled with minerals:




...and then we were off to Field Study Area #3...

Labels: appalachians, basalt, field trips, igneous, metamorphism, national parks, primary structures, proterozoic, shenandoah, structure, teaching

I took my Structural Geology students on a three-day field trip this weekend to examine outcrops in the Blue Ridge and Valley & Ridge geologic provinces. Here's a few photos of the team at our first (of four) field study areas, the Garth Run high-strain zone:

Examining the structure and taking strikes and dips:






Fabric elements cross-cutting one another:


Mylonitic fabric:


Foliation wrapping around a feldspar porphyroclast:


This is kind of interesting: a big pancake (oblate ellipsoid) of blue quartz, with a potassium feldspar in the middle:


And if you zoom in close, you can see that the feldspar porphyroclast is broken in the middle (along the plane of cleavage) with non-blue quartz filling in the gaps:


I think this blue quartz likely formed in the pressure shadow of the resistant feldspar porphyroclast during flattening strain, and eventually that feldspar began to brittlely deform, extending in the direction of minimum principal stress.

Quite a bit of variation across strike:


The students found some nice euhedral garnets too, though this was a block of float from upstream, and not intimately associated with the high-strain zone itself:


More tomorrow, from Field Study Area #2...

Labels: blue ridge, field trips, igneous, metamorphism, structure, teaching, valley and ridge

Almost a week after the field trip to Old Rag Mountain, and the Facebook-hosted pictures keep trickling in. Here's some shots by NOVA student Eileen Lodovichetti, and an ensuing discussion of feeder dikes and supercontinent breakup.

Here's a shot of the upper reaches of Old Rag, showing the characteristic spheroidal weathering of the Old Rag Granite and the relative lack of trees on top:

photo by Eileen Lodovichetti

...And here's a shot that Eileen took which shows the interior of one of the weathered-out feeder dikes we had to hike through on our way to the summit. You can actually see the classic geoprofessorial arm-waving caught in blurry motion!

photo by Eileen Lodovichetti

This is one of the coolest things about hiking Old Rag: after scrambling up on top of spheroidally-weathered granite domes, you drop into these tabular "hallways." The astute observer will note that the floor is made of a fine-grained, dark-green-colored rock, quite distinct from the light-colored, coarse-grained granite that makes up most of the mountain. These are dikes of metamorphosed basalt that intruded the granite during the breakup of the supercontinent Rodinia in the Neoproterozoic era of geologic time.

Here's one of my former Field Studies in Geology students, Mike Nelson, pointing out a similar dike along Skyline Drive, in the main part of the park:


Basically, the story goes like this: Around 1.2 to 1.0 Ga, continental fragments amalgamated into a supercontinent called Rodinia. In Virginia, this is recorded in the rocks of the Blue Ridge province, where the basement consists of granitoids (granites and related rocks) and metamorphosed granitoids (gneisses, mylonites). Among the youngest of these is the Old Rag Granite, which intruded the Pedlar Formation granite gness around 1.0 Ga.

Later, Rodinia broke apart, resulting in an extensional tectonic regime and mafic volcanism. Fractures opened up in the Old Rag Granite and funneled mafic magma towards the surface. Massive eruptions of basalt blanketed the landscape. The resulting layers of basaltic lava are known as the Catoctin Formation. At Old Rag Mountain, we can see some of the plumbing that led to these flood basalt eruptions: these are feeder dikes, because they "fed" the eruption above them.

Because the dikes (which were metamorphosed to greenstone during ~300 Ma Appalachian mountain-building) weather more rapidly than the Old Rag Granite, they are typically recessed into the landscape. That's what makes the "hallways" in the photograph above. Here's two more images, showing these weathered-out feeder dikes:



Check out how there's moderately-developed columnar jointing extending across the dike. These columns form perpendicular to the cooling front, and the dikes would have lost their heat out the sides. In horizontal lava flows, the heat is lost from the top and bottom surfaces, so you get vertical columns. Here, a vertical dike produces horizontally-oriented columns. Hikers appreciate these "steps" as they squeeze through the dikes on their way up the mountain.

Here's a map of part of Shenandoah National Park:


Please ignore the "hover" instructions at the lower right. I've reproduced the "hoverable" image below. Key: the orange is the Pedlar Formation. The pink is the Old Rag Granite, and the green is the Catoctin Formation. Feeder dikes of the Catoctin are shown as green lines.

Now, let's take away the map, and just preserve the orientation of the feeder dikes. This will tell us the overall tectonic stretching direction:
Various plate reconstructions show either Amazonia or the Congo craton offboard of Virginia at the time Rodinia broke apart and the Iapetus Ocean began seafloor spreading. I've illustrated it here as the Congo, but that might be wrong.

So: the hike up Old Rag is great exercise, and offers scenic views, but for those willing to consider the rocks and how they got there, it's an insightful view into the tectonic past.

Lastly, here's a lovely, well-developed weathering rind on the Catoctin meta-basalt (greenstone). When the dark green rock adjusts to the conditions at the Earth's surface, it breaks down, resulting in the tan/"buff" color on the outside. You're watching the rock "rot" from the outside surface, working its way inward:


More on the geology of Shenandoah National Park can be seen at this page on my website.

Labels: appalachians, basalt, blue ridge, field trips, metamorphism, mountains, national parks, nova, plate tectonics, shenandoah, structure, weathering

Last weekend, I took a group of students, mostly from NOVA but also 3 from GMU, up to hike Old Rag Mountain in Shenandoah National Park.

Here's a Google Map showing the terrain (and trails, which is a cool new addition to the already cool Google Maps):


The crew discusses debris flow deposits in the forest on the way up the mountain:

photograph by Charlie Corrick

The first spot where we get a nice view out over the valleys below:

photograph by Charlie Corrick

Spheroidal weathering in Catoctin Formation greenstone:

photograph by Jared Fortner

Spheroidal weathering in granite (the Old Rag Granite, 1.0 Ga):

photograph by Charlie Corrick


photograph by Charlie Corrick

Student Jared atop a spheroidally-weathered boulder of the Old Rag Granite:

photograph by me

Grain-size differences in the Old Rag Granite (balanced atop my leg):

photograph by me

Non-foliated Old Rag Granite (showing lovely "blue quartz"):

photograph by me

And the foliated version of the Old Rag Granite:

photograph by me

Labels: appalachians, basalt, blue ridge, field trips, geology, granite, igneous, mountains, national parks, nova, structure, weathering

Here's some photos from today's Physical Geology class field trip to the Billy Goat Trail. It actually snowed on us a little bit... cold! My student Luke O'Neil took all of these, hosted on his Facebook page, and this is an experiment to see if I can post Facebook photos on my blog... keeping my fingers crossed...

Migmatite:


Il profesore showing tilted tree trunks (knocked in a downstream direction during floods):


Folded graded bed in metagreywacke:


Students circle around an exotic boulder of the Catoctin Formation greenstone (from the Blue Ridge province); the boulder was transported downstream by the ancestral Potomac River when it was flowing on the Bear Island strath, before incision and abandonment of the former river bottom to become a bedrock terrace:

Labels: field trips, geology, maryland, national parks, nova, piedmont, rivers, teaching

Last week, I updated my field trip photo page with a fresh batch of images from last spring's Field Studies in Geology course to the Billy Goat Trail. Here are the new shots:












All photos are by Kevin Mattingly, NOVA photographer.

Labels: field trips, maryland, nova, piedmont, teaching

GSW Spring Field Trip: Sunday, May 17, 2009

The Potomac Gorge: An Extraordinary Meeting Place of Geological and Biological Diversity

Led by: Tony Fleming, Natural Areas Geologist, and Gary Fleming, Vegetation Ecologist, Virginia Department of Conservation and Recreation

The Potomac Gorge between Great Falls and Georgetown is recognized as one of the most biologically diverse sites in the eastern United States, with an unusually large concentration of rare flora, fauna, and natural communities. For more than a century, the gorge has also enjoyed an iconic reputation as the region's premier geological area, both for its exceptional exposures of Piedmont bedrock and the complex tectonic history they reveal, and for the natural fluvial cycle of flood disturbance that still operates on the Potomac, the only Fall Zone river of its size whose flow is not altered by dams. Geology and ecology converge on this field trip, as we visit two sites where geologic processes exert a powerful influence on the distribution of unusual natural communities. At Turkey Run Park, we will hike past steep boulderfield communities and regionally rare sugar maple/mixed mesophytic forests more typical of New England, here growing on soils weathered from basic intrusive rocks in a cool microclimate created by processes driven by Pleistocene glaciation and the ongoing southward migration of the Potomac Valley. Chain Bridge Flats, by contrast, is a unique flood-scoured bedrock terrace hundreds of hectares in size that displays a complete ecotone of communities adapted to progressive changes in the form and intensity of natural flood disturbance as one approaches the river. Among these are disjunct, prairie grasslands containing calcium-loving plants more typical of the Midwest and Great Lakes. This site also is the largest and cleanest exposure anywhere in the Piedmont of the Sykesville Formation, the enigmatic and often inscrutable submarine trench deposit from the Taconic subduction zone that makes up much of the local bedrock. Here, a phenomenal array of textures, exotic inclusions, mega stratification, volcanic detritus, and metamorphic features can be seen together at a clarity and scale unlike anywhere else, providing insights into the origin of this enormous sedimentary melange.

Key Topics: Ecogeology; Georgetown Intrusive Suite; Sykesville Formation; Pleistocene and Holocene history of the Potomac Gorge; weathering, ground water, and nutrient cycling; flood frequency and dynamics

Field Trip Details: Hike departs promptly at 9:30 AM from lot C-1 at Turkey Run Park, and will follow the Potomac Heritage Trail towards Dead Run, returning to the parking lot by around noon. Eat lunch at the picnic area overlooking the old soapstone quarry at Turkey Run, before driving across the river to Chain Bridge Flats. Afternoon hike will depart around 1:30 from the parking area on Clara Barton Parkway immediately north of Chain Bridge, and will follow the towpath and ACE spillway out to the flats. Return by 4 PM. Expect spring wildflowers, poison ivy, some steep grades at Turkey Run, and rough terrain involving scrambling on rocks at Chain Bridge Flats. Sturdy footwear is a must. Bring lunch, snacks, and water. Restrooms are available at Turkey Run Park, but not at Chain Bridge Flats.

Questions? Contact Bill Burton at bburton@usgs.gov

Labels: field trips, gsw, piedmont, plants, rivers

Yesterday, four Honors students and I went out to West Virginia's route 55 (between Wardensville and Moorefield), to look at some sedimentary strata and associated tectonic structures. Our guide was my friend David Dantzler, an enthusiastic amateur geologist. Here's a map of the terrain we traversed:



As you can see, this is part of the Valley & Ridge province, an area of the country defined by Paleozoic rocks that were folded and thrust-faulted during the Alleghenian phase of Appalachian mountain-building. Recently, a new road has been constructed traversing these valleys and ridges. It's a bit of a boondoggle, a pet project of West Virginia senator Robert Byrd which funneled federal dollars into the Mountain State, ostensibly to make it easier for the chicken farmers of Moorefield to get their birdie bits to market on the east coast.

This image ought to give you a sense of the project's scale (big bridge), and how much use it gets (no one on the bridge):


But the U.S. taxpayer's loss is the geologist's gain... There are some pretty spectacular new exposures of Valley & Ridge rocks along the new route 55. Here's the NOVA van parked at an outcrop of Tuscarora Sandstone that is arched up into a broad anticline. Again, notice how few people are driving on route 55 here:


Ooh, look: heavy traffic!


Contact between the lower Tuscarora Sandstone (a Silurian-aged extremely pure quartz sandstone, variably fused to quartzite), and the overlying (darker-colored) formation, which is either the Rose Hill Formation or the Mackenzie Formation at this location:


We found oodles of cool trace fossils:







But it wasn't just sedimentary layers. There were also some cool tectonic structures, like this joint in the Tuscarora, showing a beautifully developed hackle fringe:



Here's some "pencil cleavage" where fine-grained shale develops cleavage that intersects the planes of fissility, causing it to fracture in long slivers:



I slammed on the brakes for this one: an awesome anticline...


I forced David and the students to act out the orientation of the bedding planes at this anticline:


Honors student Jason points out a small thrust fault in the outcrop above him: You can see the offset in a greenish/gray shale layer:


In case it wasn't obvious above, here's a zoomed-in shot, with the offset layer highlighted (the miracles of Photoshop!) and the fault labeled:


We all had a grand day outside, and the rain held off until our return trip, which was pretty great. Thanks to David for showing us these rocks, and thanks to my students for being smart and inquisitive and into field trips.

Labels: appalachians, devonian, field trips, fossils, mountains, nova, politics, primary structures, sediment, silurian, structure, teaching, valley and ridge, west virginia

It's getting to be springtime... and that means field trips!

My first field trip of the semester is tomorrow: my friend David Dantzler has organized a trip to look at stratigraphy and structure out on a new highway in West Virginia. I'm supplying half a dozen Honors students and a NOVA minivan, but David's handling the content. And of course, I'll be on hand to comment on "teachable moments." Looking forward to it.

Other trips upcoming this semester: Billy Goat Trail (x4!), Massanutten Mountain, Old Rag Mountain, Washington DC walking tour, and a weekend-long structural geology trip to the Blue Ridge and Valley & Ridge provinces. I love field trips; really they were the aspect of majoring in geology that appealed to me the most - the fascination with Earth processes took longer to develop.

See you in the field!

Labels: blue ridge, field trips, maryland, nova, piedmont, teaching, valley and ridge, virginia, west virginia

GeoTripper asks about where should be the top places geologists should visit? Or more specifically: What are the places and events that you think should all geologists should see and experience before they die? What are the places you know and love that best exemplify geological principles and processes?

He's asked this question before, and it set off a satisfying kerfuffle in the geoblogosphere. "Satisfying" because lots of geobloggers chimed and shared their experiences (like me). "Kerfuffle" because it's fun to say... Um, also because the original "Geologist's Life List"was pretty America-focused. A few days later, I posted a series of suggestions for revisions to the list, and now I repost them in honor of the upcoming Accretionary Wedge, with some addenda and modifications:

Specific places

1. Do an Appalachian transect through the following physiographic provinces: Piedmont, Blue Ridge, Valley & Ridge, and Appalachian Plateau
2. Visit the Chalk (England, France, Ireland...)
3. Visit Iceland's Thingvellir Valley to see the mid-Atlantic divergent plate boundary
4. Visit Mt. Fuji, Japan
5. Visit Great Barrier Reef, Australia
6. Visit Ayers Rock (Uluru) Australia
7. Visit the Himalayas (Kashmir?)
8. Visit the Tibetan Plateau
9. Visit the Gobi Desert
10. Visit the Sahara Desert
11. Visit the Sonoran Desert (for the saguaros)
12. Visit the Atacama Desert
13. Visit the Rub' al Khali (Empty Quarter)
14. Visit Beijing or Shanghai (for the perspective on what really dirty air looks like)
15. Visit the big island of Hawai'i
16. Visit Yellowstone
17. Visit the Galapagos Islands
18. Visit Madagascar (for the lemurs)
19. Visit Patagonia
20. Visit the Andes
21. Visit the Alps
22. Visit the Canadian Rockies
23. Visit Wrangell-St. Elias National Park, Alaska (and/or neighboring Kluane National Park in the Yukon Territory)
24. Visit Denali, Alaska
25. Visit the Aleutian Islands
26. Visit Mount Everest, the highest point above sea level.
27. Visit Chimborazo, Ecuador (furthest point from the center of the Earth, due to the equatorial bulge)
28. Visit Mauna Kea, the tallest mountain above its base.
29. Visit Antarctica
30. Visit the Siberian Traps
31. Visit the Deccan Traps
32. Visit the Columbia River flood basalt province
33. Visit Sumatra/Krakatau/Java, Indonesia
34. Visit the South Island of New Zealand
35. Visit the Dead Sea
36. Visit the Giant's Causeway, County Antrim, Northern Ireland.
37. Visit the Great Rift Valley of East Africa
38. Visit the Nile River
39. Visit the Mississippi River
40. Visit the Amazon River
41. Visit the Grand Canyon
42. Visit the Owens Valley, California (or anywhere in the Basin & Range, but the Owens Valley is pretty darned special, and geologically diverse)
43. Visit Gros Morne National Park, Newfoundland, Canada (walk on the "Moho")
44. Visit Siccar Point, Scotland (for the unconformity)
45. Visit Gibraltar, "UK"
46. Visit Vesuvius, Pompei, and the Pompei-to-be, Naples
47. Visit Victoria Falls
48. Visit Racetrack Playa's sailing stones, Death Valley
49. Visit Devils Tower, Wyoming
50. Visit the Moon

Geological features

1. A tectonic triple junction (Mendocino, CA is an example, or northern Burma, or Panama)
2. Tower karst (Guilin, China, or southwestern Thailand are examples)
3. Experience a regional flood
4. Experience a flash flood
5. Experience an earthquake
6. Ediacaran fauna fossils in situ (possibilities include the type locality of the Ediacaran Hills in Australia, or Charnwood Forest in England, the White Sea region in Russia, or maybe the Avalon Peninsula in Newfoundland)
7. Vertebrate fossils in situ
8. Visiting a laggerstatten site (e.g., Burgess Shale, Chenjiang, Sirius Passet, Solnhofen)
9. An alpine glacier
10. A continental glacier (ice cap or ice sheet)
11. A kimberlite pipe (preferably with diamonds, and good luck with that)
12. A coral atoll (take your pick)
13. A meteor impact crater (not a buried one, either)
14. A big river delta (Mississippi, Ganges, Nile, or any of the dozens of others)
15. Barrier islands (Padre Island, Texas, and the Outer Banks of North Carolina come to mind, but I'm sure there are others on other continents)
16. A craton (Canadian shield, Kaapvaal, North China, etc. etc. etc.)
17. A big estuary (Cook Inlet, Chesapeake Bay, Bay of Fundy: all North American examples. Give me some others)
18. See some karst.
19. Kayak (or other boat) through a fjord.
20. See a dropstone.
21. See an ophiolite.
22. Visit a major stike-slip fault (San Andreas in USA/Mexico, or North Anatolian in Turkey, or Tan Lo (sp?) in China)
23. Visit a nappe or thrust sheet (Glarus Thrust in the Alps, Chief Mountain/Glacier NP in Montana, Blue Ridge in Virginia/North Carolina)
24. Visit a really big cave (Mammoth, Lechugilla, or some other that I don't know about on another continent)
25. (#25-29 on this list is derived from Christie at the Cape's post on this topic...) See a famous "big wave" e.g. Maverics or Dungeons, breaking.
26. Watch a glacier calving into the sea.
27. Listen to singing beaches or dunes.
28. Walk across and observe a metamorphic aureole (like the classic Barrovian sequence in Scotland.
29. See a tidal bore.

Activities and experiences

1. A world-class natural history museum (London Museum of Natural History, American Museum of Natural History, and the Smithsonian's National Museum of Natural History all come to mind.)
2. Meeting of a classic scientific society (Royal Society, Explorers Club, Cosmos Club...)
3. Do some original research.
4. Present your research at a meeting of other scientists.
5. Publish your research in a peer-reviewed scientific journal.
6. Visit an original copy of "map that changed the world" (William Smith's geologic map of England, Wales, and part of Scotland)
7. Experience a big earthquake (greater than 5.0 sounds like as good a cut-off as any)
8. Experience a volcano erupting something other than gases (lava, pyroclastics)
9. Go ice fishing (or just out onto a frozen lake/pond/sea/ocean and ponder the improbable nature of ice and how it freezes from the top down, preserving the living things underneath, like fish. Without this odd property, it would be tough to maintain freshwater lake life at high-latitudes/elevations through the winter months.)
10. Compare and contrast El Nino and La Nina by personally living through both in the same spot. (e.g., Peru, southwest U.S., Papua New Guinea, Australia)
11. Go on an oceanographic research cruise for more than two weeks at sea.
12. Experience a hurricane/typhoon/cyclone (preferably surviving it)

I welcome your additions and comments! Or just tune in for the Wedge when GeoTripper posts it.

Labels: blogs, field trips, geologists, geology, travel

Just got a batch of images from the NOVA photographer, Kevin Mattingly. I particularly like this image of last spring's Field Studies class at the Billy Goat Trail:

Here, we're overlooking the upstream end of Mather Gorge, checking out some ~360 Ma lamprophyre dikes exposed there -- but offset on either side of the river!

Labels: devonian, field trips, national parks, nova, piedmont, teaching

One of my favorite hiking and geologizing destinations, the Billy Goat Trail (in C&O Canal National Historical Park) was the site of a gruesome discovery Saturday: a dead body! More here from MSNBC. Hat tip to Michelle A. for the prompt notification.

UPDATE: Same info, but from the Post.

Labels: field trips, maryland, news, piedmont

A special request from my fellow GSW member Nora Noffke (Old Dominion University), about a site in South Africa that Chris Rowan blogged about in May of this year:

The scenic Wit Mfolozi River Gorge in South Africa displays unique and spectacularly preserved sedimentary structures caused by microbial mats that colonized a sandy coastal area that are 3 billion years old. A comparison with modern microbial mats in a similar setting today suggests that the mat-constructing microbiota may have been cyanobacteria, possibly the oldest known in Earth history (GSA Today, October 2008).

In collaboration with the Society for Sedimentary Geology (SEPM), the Geological Society of America (GSA) and as part of the Year of the Planet Earth (IYPE), the Geological Society of South Africa (GSSA) is establishing the "Wit Mfolozi River Area" as a Geoheritage Site. This Geoheritage Site will serve visiting scientists, students and the interested public in leaning more about the Archean world and Earth's earliest life.

With the support of funds raised around the world, GSSA will set up the logistical and administrative infrastructure necessary to preserve and make this site available to all. This includes, for example, the construction of secure access to the site, installment of signs explaining the details of biogenic sedimentary structures at different spots in the outcrop and also measures to protect the site from damaging flooding by the river.

For further information about the site contact Roger Price (Geosite Conservation Committee, GSSA - rprice@geoscience.org.za), Nora Nofke (Old Dominion University and GSA Division of Geobiology and Geomicrobiology - nnofke@odu.edu) or Wesley Hill (GSA - hill@geosociety.org).

For donations to the fund for the site please contact Theresa Scott (SEPM - tscott@sepm.org).

Thank you very much,
Nora Noffke

Labels: action, africa, blogs, field trips, gsw

Dave at the Geology News blog is hosting this month's Accretionary Wedge on the topic of "favorite places to do field work."

My favorite place to do field work is in California's "range of light," the Sierra Nevada.

I did my geology master's field work in the eastern Sierra, along the Sierra Crest Shear Zone, a major high-strain zone which parallels the eastern edge of the Sierra Nevada Batholith through older meta-sedimentary and meta-volcanic host rocks.

In 2003, I spent the summer out there, starting with my first field area at lovely Gem Lake:

An angular unconformity can be seen in this image as the tilted (close to vertical) metasedimentary and metavolcanic rocks (orange and gray) are overlain by dark colored "Tertiary" basalt flows. A big talus slope of basalt chunks makes a black triangular shape that heads downhill toward the lake. In the distance, where the land rises appreciably, the granites (and granodiorites) of the batholilth begin.

We camped on this peninsula sticking out into Gem Lake:


Dazhi Jiang (Then of UMD-College Park; now at the University of Western Ontario) and USC's Geoff Pignotta examine strained metavolcanics near Gem Lake:


Here's me with the Ritter Range in the background:


Glacial striations sculpting my strained metavolcanics:



Field gear:

Labels: california, field trips, glacial landforms, granite, igneous, metamorphism, structure, travel

Yesterday, I took a three Honors students and a colleague to Difficult Run, Virginia. This is a hiking trail that goes from Georgetown Pike, in the tony neighborhood of McLean, Virginia, down through a deep, steep river valley to the Potomac River.

As noted a couple days ago, the trail is right across the Potomac River from my beloved Billy Goat Trail. In a recap from that post, here's a map of the area... Feel free to switch it to "satellite" view.



Some discussion of the bedrock geology of Difficult Run can be found here, in an excellent field trip guide by Scott Southworth (USGS) and colleagues that's part of Excursions in Geology and History (Frank Pazzaglia, editor).

We began our trip by meeting up with Doug Dupin of the Palisades Museum of Prehistory, who joined us for our exploratory geohike. We walked a short distance down the trail and found a big (abandoned) quarry where it was rumored there was a good fault. This is one of these pieces of information that I heard somewhere, at some point. I couldn't find it in any literature, so maybe I heard it in discussion when I taught at George Mason University for a year between grad school and when I got my position at NOVA. Anyhow, I had never actually checked it out...

...So our first order of business was to review the criteria for identifying a fault: What would we look for? Fault breccia, fault gouge, slickensides, hydrous mineral veins, and of course, offset. However, here in the Virginia Piedmont, it's rare to have a good marker unit to compare on opposite sides of the fault: usually it's just schist on one side, schist on the other. In some places, you could add the presence of a fault scarp to that list, but being as how this was an old quarry, geomorphic features like that didn't seem likely. So our search focused on the search for fault breccia, fault gouge, veins of odd minerals, and slickensides.

A few minutes in, we found some slickensides on this boulder of float:

This is a boulder of migmatitic phyllonite, with a wavy texture due to mylonitic flow at depth. (The picture doesn't show this very well at all, though you can see faint undulations 'cascading' from the top of the photo towards the bottom. It's much clearer in cross-section.) Anyhow, the 'slicks' are a faint upper-left to lower-right lineation seen on this surface, one or two degrees off from the orientation of the ballpoint pen. The surface you're looking at here was a fault plane at some point in its history. Ballpoint pen for scale.

We did eventually locate the fault, uphill from this boulder. It was characterized by a zone of fault gouge (pulverized rock), three inches wide to a foot wide in places, and highly oxidized (presumably by oxygen-rich meteoric waters percolating along this fractured surface)... but there were no good marker units to judge the total offset.

Here's a different section through a similar rock (though I wouldn't apply the "phyllonite" textural description to this one). Instead of looking at the plane of foliation here, we're looking at a surface which is perpendicular to the foliation plane(s)....

Here in this image, you can see two cleavages... One which runs roughly upper-left to lower-right through the photo, defined by gneissic banding including bands of granite (light-colored; late Ordovician in age... Taconian Orogeny). A second cleavage runs roughly left-to-right through this photo. This second cleavage overprints the first. The overall interpretation is that the first cleavage developed due to lower-left-to-upper-right compression, forming the foliation defined by alternating bands of different compositions of minerals in an upper-left to lower-right direction. The second cleavage formed due to compressive stress sub-parallel to the pre-existing foliation, deforming it into a series of tight folds. The limbs of these folds line up parallel to one another, defining the second-generation, overprinting cleavage. Can anyone else add to this interpretation? Dime for scale.

Along Difficult Run itself, the outcrops were all relatively recently scoured (in 1972 by Hurricane Agnes), so there are some good exposures. As I noted earlier this week, the area shows some nice exposures of granite pegmatites (keys, and the edge of the Pazzaglia volume, for scale):


On our field trip yesterday, we took at closer look at these beautiful pegmatites, and the associated amphibolite bodies. Take a look at this close-up... Dime for scale.

What's going on here? You've got a beautiful (euhedral/subhedral) example of an orthoclase feldspar ("potassium feldspar") crystal amid a bunch of quartz. But look closer at the feldspar crystal... this sucker has been fractured in many places, and it's shot through with very small veins of quartz. Somehow, as this pegmatite dike was cooling, the earlier-crystallizing feldspar was broken and intruded by the presumably-still-fluid silica-rich magma. Anybody able to expand on this interpretation and shed some light on how this all played out? Or contradict it and give a different story to explain this relationship?

In the neighboring amphibolite, we checked out these cool ridges of resistant rock which are centered on thin fractures. Here, you see a couple of intersecting joint sets, each of which was the "plumbing system" for silica-rich hydrothermal fluids (my interpretation). These silica-rich hydrothermal fluids impregnated the surrounding amphibolite with quartz, which made the immediately-adjacent areas more silica-rich, and hence more resistant to weathering and erosion: Hence, now that they've made it to the surface, they're weathering out in high-relief. Dime for scale.


A bit further downstream, Doug showed us a 'cave' (central dark area, just to the right of the waterfall) between the bedrock and a big slab of sloughed-off migmatitic metagraywacke:

We each edged into the 'cave' to the end, where Doug has shown that a distinctly-rectangularly shaped hole admits a direct beam of sunlight during the fall and spring equinoxes. From the inside, it's a striking arrangement, enough to make you wonder whether it's anthropogenic. However, from the outside I was unconvinced that the hole's position was anything other than natural. Doug's initial intepretation of the site was strongly influenced by the fact that there are some unambiguous petroglyphs a short distance away from here, and based on this proximity, I think it's acceptable to infer that Native Americans may have visited this cave. However, I interpreted the opening to be completely natural, with no need to invoke anthropogenic modification in any way.

We hiked on along a ridge overlooking Mather Gorge, sighting a fox and an accipiter (Coopers? Sharp-shinned?) and a few vultures, and returned to the parking lot as the sun dipped low in the sky. On the way back to campus, Honors students Ana and Hope fed us Swiss cookies and cheese & crackers. Altogether, it was a pretty great way to spend a November afternoon...

Labels: birdies, faults, field trips, granite, igneous, metamorphism, ordovician, piedmont, rivers, virginia

Last week was field trip week for me. I led trips to the Billy Goat Trail on Tuesday and Thursday, and to Washington, DC, on Saturday.

On the Physical Geology field trip to the Billy Goat Trail, we saw rocks like amphibolite, metagraywacke, and migmatite:







Hope and Ana checking out the migmatite:


The group poses with the migmatite, to show how close anatexis is to their hearts...


Jane examines lamprophyre in a weathered-out dike:


Noting the characteristics of metagraywacke:




Traversing 'Pothole Alley'... Joel looks chilly...


Our lunch spot... Alex pretends to dive into the Potomac River...


Traversing 'The Traverse':


On the Historical Geology field trip to DC on Saturday, we were amused to find a jack-o-lantern that had facial hair resembling mine...



But that's not all! We also saw some geology. While you can get a more complete picture at my "DC Rocks" webpage, I'll post a few new photos of new outcrops here...

Here's a nice slab of granite (very angular) set in metagraywacke matrix (metamorphosed accretionary wedge complex)...


Here's two members of the Georgetown Intrusive Suite, showing the (earlier) gabbro stoping xenoliths into the (later) granite:


I love field trips. I love seeing my students light up at being outside, at getting a handle on the stuff we talk about all semester in class. I think field trips are super duper important.

Labels: dc, field trips, granite, igneous, maryland, metamorphism, nova, piedmont, teaching, xenoliths

My favorites from a recent raft of geoblogosphere posts:

• Field work on sedimentary rocks in the Dead Sea region of Jordan (from Nologic)
• Anomalocaris fossils (from Ediacaran)
• Charming but obsolete mining terms (from Hypocentre)
• Other cool stuff in a similar conglomeration from BrianR (at Clastic Detritus)

Labels: blogs, field trips, fossils, geology, mining

Yesterday was the Geological Society of Washington's fall field trip. A group of about twenty of us went down to George Washington Birthplace National Monument, a stretch of land in the Virginia Coastal Plain, about an hour east of Fredericksburg. The trip was lead by Wayne Newell of the USGS in Reston and Rijk Morawe of the National Park Service.

Here's a map of the Monument, adjacent to a small bay formed as the valley of Popes Creek flooded with post-glacial sea-level rise (essentially the story of the entire Chesapeake Bay in miniature):


Wayne and Rijk are studying the coastal processes here in an attempt to use the Popes Creek as an analogue for Chesapeake Bay processes in general. One of the reasons they really like it is because unlike other small bays in the area, it has a spit (almost a baymouth bar) protecting it from the ravages of the tidewater Potomac (which it flows into). Here's the spit heading southeast across the mouth of Popes Creek Bay:


This rotted old wooden seawall was erected along the coast in the 1960s. This is on the Potomac, just upstream from the Popes Creek Bay. Effectively, this seawall serves as a "before" line, a marker which conveys the shoreline's former position. You can see how much erosion has taken place since then:


I'm less interested in these coastal dynamics, though, than I am in the bedrock geology. There were some bluffs along the river which exposed the Miocene Calvert Formation (clay-rich lower unit) topped by a foot-thick diamictite unit, and then well-rounded river gravels on top of that:


Here's Merily (sp?) from AGI checking out the sequence of strata:


My favorite part of the trip was looking at the variety of cobbles on the beach. These cobbles are derived from all of the mid-Atlantic's physiographic provinces within the Potomac River's watershed (Valley & Ridge, Blue Ridge, Culpeper Basin, Piedmont, Coastal Plain). All those physiographic provinces have been weathered to produce the sediment that the Coastal Plain is made of. In spite of their diminutive size, they give insights into the geologic history of Virginia over the past billion years. So if you're familiar with Virginia geology, you will see some familiar rocks here.

For instance, there were a lot of these Skolithos-bearing quartzite cobbles. These are pieces of the Antietam Formation, a meta-quartz-sandstone that crops out in the Blue Ridge province, many many miles upstream:


Skolithos is the name given to vertically-oriented cylindrical burrow trace fossils, which start showing up in the Cambrian period of geologic time, indicating the evolution of vascularized bodies among animals. They are usually interpreted as worm burrows. This cobble shows several different diameters of Skolithos tubes:


Here's a cobble of another distinctive Blue Ridge rock. This amygdular meta-basalt is a piece of the Catoctin Formation, a sequence of (mainly) mafic lava flows that erupted as the supercontinent Rodinia was breaking up in the Neoproterozoic era of geologic time. The white spots you see are amygdules: vesicles that have been filled in by mineral deposits. When lava erupts, it degasses. If the lava cools into extrusive igneous rock before the bubbles have a chance to pop, little round holes are preserved in the rock, like Swiss cheese. We call these "vesicles." When vesicles get filled in with deposits of minerals (from groundwater passing through the rock), they are called "amygdules," from the Latin for "almond," which I guess they resemble in an ellipsoidal sort of way:

(I showcased a very similar cobble here in March of this year.) Like the Antietam Formation cobbles, this Catoctin Formation cobble originated in the Blue Ridge province, and has tumbled dozens of miles downstream to end up out here on the Coastal Plain.

Here's one from even further away! This is a cobble of flint from one of the limestone units out in the Shenandoah Valley, the easternmost valley of the Valley & Ridge province. (I've previously posted on those rocks, too.) While the limestone which originally hosted this flint nodule has weathered away, the flint is microcrystalline silica: very hard, very chemically stable. It's a common cobble to find surviving out here in the Coastal Plain:

We also found some rocks that are distinctive occupants of the Culpeper Basin, a Triassic-Jurassic rift valley upstream. Here's a chunk of the Manassas Sandstone Formation, another rock that has been previously mentioned on this blog:


The rock I spend most of my time thinking about is the metagraywacke of the Mather Gorge Formation. (For one mention on NOVA Geoblog, click here.) Here's a piece of it that looks identical to the rocks you'll see near Chain Bridge, DC, or along the Billy Goat Trail (Potomac, Maryland):

This rock was metamorphosed ~460 million years ago, in the late Ordovician, although the original sediments are older than that: perhaps Cambrian or late Neoproterozoic in depositional age. This sample even had a little bit of hydrothermal quartz stuck to it, a common feature of Piedmont metamorphics...

Having covered clasts derived from the Valley and Ridge province, the Blue Ridge province, the Culpeper Basin sub-province, and the Piedmont province, there's nothing left in the Potomac River watershed except for the Coastal Plain itself. And sure enough, we saw Coastal Plain clasts too. Here's a chunk of the Calvert Formation that GSW Field Trip Chair Bill Burton found: He cracked it open and found a shark tooth fossil inside:

This is the first time I've ever seen a tooth preserved as a carbon film. Except it wasn't really just a film, it was more a three-dimensional external mold with a carbon film, and little nuggets of carbonaceous material rattling around inside. Shark's teeth are pretty common in Miocene deposits on the Coastal Plain, including C. megalodon teeth, but this style of preservation was pretty novel for me. If you're into fossil collecting, don't go to George Washington Birthplace National Monument, because collecting isn't allowed there. However, nearby Westmoreland State Park offers legal fossil collecting opportunities. It's about ten minutes further south.

I'd like to thank the field trip leaders and Bill Burton for organizing the trip. I enjoyed the excursion!

Labels: coastal plain, field trips, flint, fossils, gsw, rivers, sediment, virginia

I was reminded this morning to update the list of activities for the coming week, including the Billy Goat Trail hike scheduled for Friday:

Wednesday evening: GSW. Free and open to the public.

Thursday: James Ussher's "birthday of the Earth." How will you be celebrating?

Friday afternoon: I'll be leading a public geology hike along the Billy Goat Trail, starting from the Great Falls Tavern Visitor Center (C&O Canal NHP) at 12:30pm, going til 4:30pm or so. Maybe 5pm. Free and open to the public.

Saturday: GSW Fall Field trip: "Tidewater Geomorphology at George Washington's Birthplace National Monument, Westmoreland County, VA." RSVP.

Labels: coastal plain, field trips, gsw, meetings, piedmont

A reminder to NOVA students, faculty, and interested area geophiles: I'll be giving a talk entitled "Two Months of Rock and Road: A North American geological road trip" today at noon as part of the Science Seminar series. It's in the CE Forum on the Annandale campus. Free and open to the public; light refreshments served.

McCain and Obama having fun: After all the rancor, this makes me happy.

If you're planning on going on the GSW Fall Field trip, let them know ASAP. They need a headcount.

The slate of speakers has been announced for next week's GSW meeting: Leonard Konikow, U.S. Geological Survey, Reston: "Ground-water depletion: National assessment and global implications;" Dionysis Foustoukos, Carnegie Institution of Washington Geophysical Laboratory "Energy sources in dark abyssal waters;" and Igor Puchtel, University of Maryland, College Park "Re-Os isotope systematics and HSE abundances of the 3.5 Ga Schapenburg komatiites, South Africa." 8pm next Wednesday at the Cosmos Club. Free and open to the public; refreshing beverages served starting at 7:30pm.

Virginia's a swing state... unbelievable and amazing.

Radioactive granite countertops cartoon caption contest reminder.

JPL has launched a new climate site:

...And congratulations to Walter Alvarez for being awarded the Vetlesen Prize.

That's all I've got. Have a good Friday!

Labels: field trips, gsw, meetings, news, politics, travel

Yesterday, I mentioned that the main point of this weekend's field trip was to attend the Virginia Geological Field Conference in Marion, Virginia.

We arrived on Friday night at Hungry Mother State Park, and got some background information and logistical direction from the trip's leaders and the various officers of the VGFC. We also got some sobering news about how Virginia budget cuts will affect the Division of Geology and Mineral Resources... but more on that tomorrow.

On Saturday morning, we headed out to examine the geology of the Pulaski and Saltville thrust blocks, two of the slices of Paleozoic sediments that got shoved bodily northwestward during the Alleghenian phase of Appalachian mountain-building. The point of the trip was to examine the structure and stratigraphy of these two thrust sheets, in an attempt to compare and contrast them. Both are an example of "thin-skinned" tectonics, where sedimentary strata are deformed (folded/faulted), but they are disconnected from the tougher underlying "basement" rocks (the crystalline rocks of the North American continent beneath). Sliding along a big basal fault called a decollement, these sheets of sedimentary rocks created the northwestern fringe of the Appalachian mountain belt; a zone called the "fold and thrust belt." (This is in contrast to the "thick-skinned" style of deformation exemplified by the Blue Ridge province immediately to the east, in which the basement rock is itself deformed, and shoved up on top of these younger sedimentary strata.)

Here's two of the three field trip leaders: Loren Raymond (holding map) and Bill Whitlock (talking into the microphone), giving us relevant details for our first field stop:


Fred Webb (the third trip leader) used the same technique of large graphics as an aid in explaining the local geology. Here, he explores the geology of Saltville, VA, from a scenic overlook:


Here's Fred and Loren using another visual prop to illuminate the distribution of sediment types (Knox dolomite versus Moshiem limestone) on a farm in the Rich Valley:

Does anyone else out there use large visual aides like these on field trips? I think it's a pretty good idea.

There were a lot of people who attended the conference: over 120! Here's the crowd at the Saltville Overlook stop:


...and the throngs of geologists shutting down traffic on the way to another stop:


...and still more geologists all over the right-of-way at our final stop of the day:

Kudos to the trip organizers for coming up with a coherent way of running the trip with so many participants!

So why were we there? ...To look at these deformed sedimentary strata, and increase our understanding of the deformation mechanisms that accomodated strain during Appalachian mountain-building. Here's a look at the Max Meadows tectonic breccia, a zone of crumbled rock at the base of the Pulaski Fault:


Just above the breccia, the rock is still pretty deformed. Here's some intense folding and boudinage in dolostone & shale layers:


At another location, Honors student Hope W. shows a fault in the Nolichucky limestone:


In other places, folds were the main variety of strain observed in the rocks. Here, we see this in the Honaker dolomite (with elbow for scale):


Ditto for this exposure of the (Cambrian) Nolichucky limestone (enthusiastic caver for scale):


After a superb lunch put on by a church group, we strolled out in some karstic fields in the Rich Valley. Here, several field trip participants drop down into a sinkhole:


I was interested to see that there were a lot of Mississippian-aged evaporite deposits in this corner of Virginia. Saltville's salt was from the Maccrady Formation, as is this gypsum (note fingernail scratch mark):


Here's the spectacular final outcrop of the day, where we looked at deformation within the Cambrian-aged Nolichucky and Honaker Formations, as well as the Mississippian-aged Maccrady Formation they override at this location on the Saltville Thrust Fault:


Of note to you environmental types out there: Saltville was not only the "salt capital of the Conferderacy," but it was also the site of the very first Superfund site (due to dumping of mercury as a byproduct of soda ash + chlorine production).


And I'll just conclude the photo section of the post with a couple of photos of cool spiders we saw. Each of these arachnids is a good three inches in length (including legs):

I think the upper one is a 'garden spider.' The bottom one is silver! I've never seen a silver spider before...


All in all, it was a good day in the field. We returned pleasantly tired and hungry, and had dinner at the Hungry Mother State Park "The Restaurant". Over food, we discussed the pros and cons of field trips like this, and slept well that night.

I was particularly pleased to meet up with and hang out with folks like Cy Galvin (part of my pre-GSW dinner group), Jon Tso (Radford University), Pete Berquist (Thomas Nelson Community College), Amy Gilmer (Virginia Division of Geology and Mineral Resources), and Chuck Bailey (College of William and Mary). Pete, Amy, Chuck, and I are all W&M geology department alumni. Chuck mentioned the good news that he will soon be joining the geoblogosphere too -- watch this site for an announcement of his (surely to be excellent) geology blog as soon as it goes live.

Labels: arthropods, conferences, field trips, nova, stratigraphy, structure, valley and ridge, virginia

This weekend, I spent three days on an extended field trip down to southwestern Virginia with NOVA adjunct geology instructor Chris Khourey and four of my Honors students. We left Annandale on Friday morning, and made our first stop at Willis Mountain, Virginia, site of one of the most productive kyanite mines in the world.

Here's a Google Map of the mountain:


The Kyanite Mining Corporation was very gracious in hosting us. I'd particularly like to thank Mike Morris, who took two hours out of his day to show us the site and the mining operation.

Why mine kyanite? It's used as a refractory mineral: that is, one that won't melt under high temperatures. A lot of their kyanite is heated in kilns to produce a second mineral, mullite. The mullite is even more stable than kyanite in high temperature refractory situations. (It won't melt until it hits over 1800 degrees C!) Additionally, they cleverly saw up big blocks into dimensional stone for countertops and the like.

The kyanite mined at Willis Mountain is in a quartzite which also includes a fair amount of pyrite and hematite. We heard about the different procedures used to extract the non-kyanite minerals so that their end product is relatively pure and of constant quality.

Here's Mike showing the overall anticlinal shape of the deposit:

It's a plunging anticline, as you can probably make out from the Google Map terrain view up top.

Some of the dimensional stone, which I think is pretty spectacular:


Close up of the kyanite (light blue, on left) in the dimensional stone.


Nearby Baker Mountain also hosts kyanite deposits, which show a deeper blue color (Mike wasn't sure why, but suggested that chromium may be responsible):


Inside a huge storage building where the mullite (white powder at our feet) is stored:


Atop Willis Mountain itself, showing the weathered kyanite quartzite exposed there:


Honors students ask questions of Mike:


Mike and Chris standing near some fresh boulders of kyanite quartzite:


It wasn't all metamorphism and mining... I also noticed these nice raindrop impressions in a drying mud puddle:


After lunch atop the mountain, we hopped back in the van and hightailed it for southwestern Virginia, on our way to the Virginia Geological Field Conference. More on that tomorrow.

Thanks again to Mike and the good folks at the Kyanite Mining Corporation for hosting our visit!

Labels: conferences, economics, field trips, metamorphism, minerals, nova, piedmont, teaching, virginia

This weekend, I took 14 NOVA students caving in West Virginia. We hit three caves in the vicinity of Franklin, WV, on Saturday. On Sunday, we headed out towards Spruce Knob to experience two terrific caves: Stillhouse and the Sinks of Gandy. Here are some photos (and a video) of those last two caves.

Stillhouse Cave:









The sinkhole out of which we crawled...


Whose helmet is that emerging?


It's Hope!


A Cecropia caterpillar (according to What's That Bug?) that Tiffany found:

Sinks of Gandy:

The crew poses at the entrance. Gandy Creek flows through the entire cave!






Exiting into the light and trees and humidity and cows:


Ricky Q, caver man extraordinaire:


Video of the final watery exit from the Sinks:

I had a great time on this trip: felt like we all really bonded and had a fun adventure. Thanks to all the students who went and to the Student Activities counselor who co-led the trip with me, Jessie Zahorian! It was fun!

Labels: caves, field trips, nova, travel

When I look back on my four years of undergraduate geology education, the one thing that strikes me as the most important thing I learned is the age of the Earth. It sent my mind reeling to recognize what a huge old planet I was on, and how ephemeral was my own species' time on it. I was a blip, a temporary arrangement of carbon, hydrogen, oxygen, and a handful of other elements that would last a while, and then disassociate. Material and energy passed into me, and out. This kinetic chemical phenomenon known as me would soon pass, and the Earth would keep turning. The human species would reach its zenith, then collapse (or evolve into something else), and the Earth would keep turning. The continents would rift and crash and the map of the Earth would soon be obselete, and the Earth would keep on turning. Climates change, meteors hit, "rivers shift, oceans fall, and mountains drift" (REM, 1985), and still the planet keeps on spinning, keeps on orbiting, keeps on keeping on.

The day I really realized the age of the Earth wasn't the day I heard "4.6 billion" in lecture. It was the day I sat there studying and grasped it internally -- it clicked that it was immensely, unimaginably old. My temporary human mind was a short-time-scale phenomenon, and it was impossible for this small cerebral system to get a grip on the true scale of the planet's age. While I would never really know (comprehend/appreciate) the age of my planet, I tapped into something fundamental that day. Looking back on it now, I'm reminded of John Playfair's words when his pal James Hutton took him to Siccar Point for the first time: "The mind seemed to grow giddy by looking so far into the abyss of time" (1805).

When I made that cognitive leap (by essentially realizing it was impossible for me to fully make the cognitive leap), I got stuck on geology. I connected to the study in a way I hadn't done before. Suddenly I was subject to a dizzying temporal vertigo, as if a layer of flooring had crumbled away leaving me gazing into a bottomless pit. The realization gave a whole new perspective on things, and it was exhilarating. It felt like one of the conversations when you're getting to know someone, and realizing that they are both intriguing and yet never completely knowable. It draws you in, connects you. Without getting too gushy, it's kind of like falling in love. I've been a geologist ever since.

As I learned more, both in school and on later peregrinations around the world, I found that geology was a great traveling companion. No matter where I went, geology was there with me, showing me new things, giving me insightful perspective. I was looking at the world through geology-colored glasses, and finding that it had a lot to show me. The world made more sense on an elemental level. Hills made sense; rivers made sense; mountains made sense. While I couldn't claim to fully understand any of these phenomena, I could claim a connection to them now that wasn't there before. They were no longer random in my mind; they had a place in the overall system, and it took geology to make me realize it.

So this perspective has stuck with me, and it's what inspired me to pitch "geology as a connector" as this month's Accretionary Wedge theme. (Newbies: the Wedge is a semi-monthly geoblogosphere carnival wherein different geobloggers contribute posts organized around a central theme.) I was curious about what I would get, and I didn't want to restrict my peers' submissions by specifying what kind of connections should be written about.

Sure enough, different people interpreted connection differently. Tromping around in the mountains doing geologic mapping yields more than insights into local structure and stratigraphy, as BrianR of Clastic Detritus discusses how his field work has connected him to the messy reality that is nature.

Jess at Magma Cum Laude is starting her first semester as a graduate T.A., and is going to employ a teaching technique that connected her to the pervasive nature of geology: everything that the Earth puts out for the purpose of assembling Oreo cookies. Something as simple as an Oreo can be the vehicle through which students realize the manifold ways they depend on the Earth every day.

Where are the boundaries between sciences? Is geology a subset of environmental science, or physics? Or both? How do we define the different parts of Nature that we study? Using a Venn diagram, Hypocentre at Hypo-theses explores the connections between geology and other sciences, particularly in the environmental realm.

Similarly, Mel uses a diagram to explore connections in her post at Ripples in Sand. How does geology connect to paleontology? Join Mel in looking at the taphonomic bridge. (And wish her congratulations on her wedding while you're at it!)

Joining the crowd in her first Accretionary Wedge post, A Life Long Scholar (at The Musings of a Life-Long Scholar) makes a connection between the very small and the very large. In trying to answer questions about massive tectonic plates, sometimes geologists must turn to little bundles of mass a few micrometers across. Check out her post to see how garnets can reveal the secret histories of the continents.

And then there are the personal connections. In Looking for Detachment, Silver Fox was the first one to submit a post on the "connection" theme with her description of how different members of the mining and exploration community connect to one another over time and space (Nevada, of course). How do Charles Manson, Kevin Bacon, and exploration geologists all fit together? Read her post to find out.

MJC Rocks of the Geotripper blog has contributed a real treat: an exploration of the connection of geologists teaching geologists through time. It turns out that his academic lineage goes all the way back to Agassiz and Cuvier! A pretty impressive consideration which will surely inspire the rest of us to investigate our own geologic pedigrees.

Finally, over at Harmonic Tremors, Julian shares a story of how his knowledge of geology led him to make a personal connection with one of his cinematic idols, director Brad Bird. If you've seen the Incredibles, you're familiar with Bird's high quality entertainment. When Julian heard that Bird was working on a movie called 1906 about the great San Francisco Earthquake, he wrote a letter to clear up some inconsistencies in the book upon which the movie is based. The talented director took the time to write back to Julian, thanking him for the "seismic tutorial."

Enjoy the various and sundry posts -- follow these digital connections to other geologists in other parts of the world, and feel connected to the larger community of earth scientists. Thanks to everyone who contributed. If I've missed anyone or if anyone wants to submit a late post, give me a shout or post a link in the comments.
________________________
References:
Playfair, John (1805). Transactions of the Royal Society of Edinburgh, vol. V, pt. III.
REM, (1985). "Feeling Gravity's Pull," Fables Of The Reconstruction, IRS records.

Labels: blogs, earthquakes, field trips, geology, metamorphism, minerals, mining, movies, plate tectonics, teaching

Here's a quick recap of my cross-country journey, for those who are interested in such things.

I left Bozeman on Saturday morning, July 26, and drove east on the Interstate to Billings, then diverged southeast towards Little Bighorn. There, I verified a comment from a Lakota friend at MSU that with my new bushy mustache (see change in icon above), I look a wee big like George Armstrong Custer (Custer & his men were killed by Lakota and/or Cheyenne warriors). After a short picnic there, I kept driving across southeast Montana, and into northeast Wyoming. My goal for the night was Devils Tower, where I have positive memories from my "North by Northwesty" roadtrip two years ago. I got to Devils Tower in mid-afternoon, just in time for a wicked-looking thunderstorm to roll in. Pendulous looking mammatus clouds were hanging down, and the skies turned a darker grey than Lola. Rain and wind came through, and a big dead branch from one of the cottonwoods in the campground came crashing down, but not on anyone's car or tent. When the skies cleared up, I drove up to the visitor's center and took a walk around the tower. It's awesome: massive columns, some of them twenty feet across. The rock is a porphyritic phonolite, and it's quite pretty to look at: big feldspars (5mm) set in a fine-grained grey matrix. Lovely.

The next morning (Sunday), I headed for Red Bird, Wyoming (along Wyoming's eastern border), where Cruisin' the Fossil Freeway suggested there would be oodles of ammonites in concretions in the Pierre Shale, some a foot across. When I visited the Denver Museum of Nature and Science earlier this summer, Kirk Johnson reiterated to me that Red Bird was the place to go for ammonites. But once I got to where Red Bird should be (according to my road atlas), there were no highway signs indicating that the town existed. Worse, there were no outcrops, and no sign of public land. (And one thing that an amateur fossil collector does not want to do in Wyoming is trespass on a rancher's land.) So, no Red Bird ammonites for me. Oh well, no worries: I had collected ammonites from a tongue of the Pierre Shale (the Bearpaw Shale) earlier in the summer on BLM land near Glendive, Montana, and scored some good specimens there. I cruised south, stopping at the Sierra Trading Post outlet in Cheyenne, Wyoming, and dropping some cash on some new duds (STP is mainly a catalog business, famous ten years ago for their amazing deals, but the company seems to be shifting to more mainstream business nowadays, including multiple brick-and-mortar locations). Then another hour on the road brought me to Fort Collins, to the house of Larry Wiseman, where I stayed earlier in my trip. He and I got some pizza and 90-Shilling Ale (Odell's) and traded tales about our summers.


The next morning, we had coffee on Larry's front porch and watch the sun rise. I packed up and hit the road, heading for Kansas. In my rear-view mirror, the Rockies shrank and vanished from sight, a melancholy fade. Out into the plains... In mid-afternoon, I rolled into Oakley, Kansas, where I headed for the Fick Museum. The Fick Museum is interesting on multiple levels: it's got some stellar fossils from Kansas's Smoky Hill Chalk (member of the Niobrara Formation), like a Xiphactinus (massive fish) and a Tylosaurus skull (even more massive mosasaur). But it's also got some whacked-out art: the founder, Vi Fick, was into making art with local "art supplies," and so the walls show his portraits of eagles rendered entirely in rattlesnake tails (see image at right, from this online gallery), or his geometric arrangements of thousands of fossil shark teeth. There's even an oil painting Fick did of "God making the Cretaceous seas," which shows a bearded diety surrounded by flames (it kind of reminded me of Hindu art) making pleisiosaurs and pterosaurs. Not the usual way you see fossils displayed, or paleontology depicted!

At the Fick Museum, I met up with Ron Schott, doyen of the geoblogosphere, who graciously agreed to show me some cool Kansas geology. Ron and I headed south from Oakley towards Monument Rocks, an outcrop of the Smoky Hill Chalk. Ron was eager to gigapan the outcrop, and he set up the little device: essentially a robot that directs his camera to take high-resolution photos in a systematic grid. Pretty cool, really -- I guess I hadn't realized what a Gigapan really was before seeing it in action. I got to meet Ron's two little plastic elves that he uses for scale, and personally placed them on a ledge of chalk for the photograph. The grid of pictures eventually gets digitally stitched together by software, and available for sharing online.

From there, Ron and I headed back up to Oakley, stopping en route so I could collect a couple samples of the aquiferiferous Ogallala Formation, and then headed east, then south again, towards Castle Rock, another chalk outcrop. Here, we tested out my Prius' shocks on the dirt tracks, and checked out the largest cliff in Kansas (nearly getting blown off it by the intense wind), and then prospected for fossils below. I found some fish scales, and a shark tooth! Also inoceramid clam fragments, encrusted with oysters (apparently a common feature of the bottom of the Western Interior Seaway). No mosasaurs, though... Back to the road, and into Hays, Kansas, where Ron put me up in his guest room. We had dinner and a few beers at the Lb. Brewing Company, and thought about recording a PodClast, but then it slipped our minds. We discussed field trips, tenure, publications, and related topics. A good time! Thanks again to Ron for being such an excellent host.

The next two days (Tuesday and Wednesday) were essentially just driving. On Tuesday, I made it to Indianapolis, Indiana, and spent the night in a hotel there. On Wednesday, I turned north, and drove up into Michigan, and crossed into Ontario at Port Huron / Sarnia. Why go to Canada on my way from Montana to DC? Well, I'm teaching my Snowball Earth class this week at NOVA, and some of the rock samples I needed were stuck at Brock University in St. Catherines, Ontario. Usually they get shipped to educators who want to use them, but because of alleged border complications, I had to go get them myself; a five hundred mile detour! Fortunately, I have good friends who leave in Waterloo, Ontario, so I went and stayed with them. Mike and Natalie Leuty have been friends since 1996, and we had a good evening catching up. They have a sweet house in a suburb full of professorial types who teach at one of the several universities in town.

On Thursday morning, Mike and I had coffee on his front porch while his kids played in the yard, and then I packed up my kit and got rolling. I made it to Brock by 11am, and got the Snowball Suite. Because it's in a giant black case that looks suspiciously like a rifle case, I packed it under a pile of other gear in my car. At any rate, I crossed back into the United States without any static from customs officials, and rolled through Buffalo, New York (twice in one year!) I made my destination for the night Ithaca, New York, where I have a friend who's going to grad school at Cornell. I've never been to Ithaca, but I hear that it's "gorges" from many people. So I called my friend, Kathryn Werntz, and she was indeed around and accepting visitors, so I drove through the finger lakes region (five subparallel glacial troughs now filled with water), and found my way to her bungalow. Kathryn and I took a walk through Cornell's campus (two amazing gorges cutting through it), had some Indian food, and went to get dessert at Purity Ice Cream.

In the morning (Friday), I got up and we went to Gimme! Coffee for some caffeine. Thus fortified, I hit the road for my final day of driving. East to I-81, then south through Pennsylvania. At Harrisburg, I turned onto I-83, which took me to Baltimore, and from there it was a familiar zoom down the B-W Parkway into northeast DC. The dome of the Captiol was visible to my left, and then the comfortable sights of Florida Avenue and U Street. Up the hill, and a left on Harvard Street, and I was back in Adams-Morgan. Home! Finally!

Labels: appalachians, canada, chalk, colorado, field trips, glacial landforms, kansas, montana, national parks, new york, snowball earth, structure, travel, wyoming

Sooo.... I've been "delinquent" about posting (if five days off counts as delinquent). But the long and the short of it is that I made it to Bozeman, and started classes, and have settled into life up here. After leaving Denver, I spent a couple days in Fort Collins, Colorado, staying with my undergaduate mentor professor Larry Wiseman. When I was at William and Mary, I forged a strong relationship with Larry, and that persisted even though I defected from biology (he's a developmental biologist, and chair emeritus of the department there) to geology (basically because they had more field trips). Anyhow, he and I would gather once a month or so for coffee and talk about life, the West, Ed Abbey, art, and science.

Now he's retired and pursuing bird rock art and also teaching cell biology at Colorado State University (in Fort Collins). We drove up to Rocky Mountain National Park and toured the various microbreweries and restaurants of Fort Collins (and Lyons). It was, in short, a good time.

Departing there on Saturday morning, I drove north through Wyoming, and camped at the end of the day at Buffalo Bill State Park, on the east flank of Yellowstone. On Sunday morning, I drove through the park, marvelling at six-foot-deep snow on Washburn Pass, and cruising along past tourists and bison galore. I stopped once, to look at the single petrified tree there, and then rocked and rolled on up the Paradise Valley to Livingston, and thence westward on the interstate to Bozeman.

In Bozeman, I'm enrolled in the Master of Science in Science Education program at Montana State University. It's essentially all science educators who are taking graduate coursework to become better science educators. And it's fun! This week, I'm taking Dave Lageson's class on the geology of the northern Rocky Mountains. More on that later, perhaps, but the point for now is that I'm enjoying it, and enjoying interacting with my fellow MSSE educators.

Tonight, I had a bonus, when we had a mini-conference of geobloggers. I guess there's somewhere around 50 geobloggers out there now, but we had four of them sitting at one table in Montana Ale Works, talking rocks and fossils and blogging and whatnot. That's got to be a record for the geoblogosphere. It was a lot of fun. Thanks to Mel, Brian, and Jeannette for making it happen!

Labels: field trips, montana, msse, travel, wyoming, yellowstone

Yesterday, I went up to Delaware Bay to help the Nature Conservancy count spawning horseshoe crabs. I carpooled with my student Efrain and his friend Dennis. We did some birding at Cape Henlopen State Park, then had dinner and a few crafty craft beers at the Dogfish Head Brewpub in Rehoboth Beach (I had crabcake, natch.), and then headed out to Big Stone Beach for the main event: the spring tide and the new moon mean spawning horseshoe crabs (Limulus polyphemus) by the thousands. We were helping the Nature Conservancy tally up the numbers of male and female crabs. You can learn more about horseshoe crabs at this excellent website. Or you can just look at these images:



























...You get the idea. Other images on the Flickr photostream. Joining a couple of medical doctors from Delaware (well, originally from Virginia, but stationed in Delaware), we surveyed the beach using TNC's rope and square-meter protocol. The weather turned cold and rainy, but we kept it up, and saw a lot of crabs. I estimate that altogether, we saw somewhere around 5,000 crabs. Pretty cool: one of the great wildlife concentrations in the world, and it's only 2.5 hours from DC. Next up: sandhill cranes on the Platte River in Nebraska, or maybe polar bears in Churchill, Manitoba...

Labels: critters, delaware, environmental, field trips, travel

My Field Studies in Geology students are required to write papers about the different outcrops we visit. Occasionally, about once per class, they write really brilliant things. Here's a quote that student Brenda used in her recent Shenandoah National Park paper:

Labels: field trips, teaching

Picking up where I left off yesterday, in describing Saturday's field trip out to western Maryland:

2:20pm: We exit Interstate 68 and go south on a dirt road for about ten or twelve miles. This road takes us through the Green Ridge State Forest, and I can tell the students are wary of it. I love a good dirt road, and this one even shows outcrops in the road surface -- resistant sedimentary layers tracing across its rutted, potholed surface. The sun comes out, and I roll down the window, relieved that the weather has finally broken.

3:00pm: We arrive at the C&O Canal's Paw Paw Tunnel, in Maryland just north of the Potomac River and the town of Paw Paw, West Virginia. ("Paw paw" is a native tree in the custard apple family with a lovely fruit also called a paw paw. They're delicious, if you can find one the raccoons haven't already claimed.) Paw Paw is the site of the most pronounced entrenched meanders seen along the length of the Potomac River. These exaggerated loops suggest an old age river system, but they are "locked" at the bottom of deep canyons, which suggests a young river system. The usual interpretation is that the Potomac is a rejuvenated river system: it was "old age," equilibrated to base level and meandering actively, but then base level dropped and it incised to a deeper level, maintaining the meandering shape even though the meanders no longer actively squiggle from side to side.

3:10pm: At the upstream end of the tunnel, we discuss the Brallier Shale (Devonian), and note the angle of the bedding here, which is tipped into the Canal's valley: ideal for landslides. When C&O Canal engineers came to the Paw Paw Bends, they faced a tough choice: construct the canal to parallel the river around its multiple entrenched meanders, or carve a tunnel through a mountain made of this stuff. They opted for the tunnel, saving 6.5 miles of Canal length, but the digging of the tunnel took 14 years!



Because the weather is good, we decide to hike over the mountain first and then walk through the tunnel on the return trip. The hike gives us views of some of the meanders' loopy shapes:



We don't see a whole lot else on the hike, but it feels good to stretch the legs.

4:oopm: We reach the Tunnel Hollow, a long linear valley on the downstream side of the tunnel. Signs of the morning's torrential rains are everywhere in the form of increased runoff. For instance, we see a large stream emerging from the base of a talus slope, flowing across the path and into the canal:



Heading up the Tunnel Hollow, we are greeted with the sight of numerous waterfalls arcing down into the valley:





Here, the layers of the Brallier Formation dip into the Tunnel Hollow, again presenting the potential for slip between the layers, and suddenly big slabs of rock dropping down into the valley. We note the "pins" holding these unstable sheets of rock in place:



4:20pm: My favorite thing about the Tunnel Hollow is the world class exposures of slickensides there. During Alleghenian mountain-building, these sheets of shale slid over one another, as a deck of cards will buckle when squeezed. Sliding between the layers ground grooves into the rock face, and also deposited mineral fibers alligned in the direction of sliding.





4:40pm: Lastly, we got to the downstream end of the Paw Paw Tunnel itself, where multiple waterfalls were cascading down onto the towpath. A fine mist fills the air, and catches the beams of sunlight. There's a nice anticline exposed just above the tunnel archway, and usually I have students climb up the stairs (on the left) to check it out up close. However, today a waterfall was landing on the stairs!







Four of us decided to go for it anyhow, just for the thrill of passing through a waterfall. Several (smarter) students who chose to stay down below pulled out their video cameras and recorded parts of our folly. Here's one showing the climb: (Unfortunately it's both silent and taken "sideways" and I'm not video-savvy enough to know how to fix it in either regard.)



Here's another video of the four of us (Nicole, Jan, Dave, and me) up on top:



4:35pm: Time to enter the tunnel. Flashlights come out, and we begin to walk through the Paw Paw Tunnel. It's a remarkable feat of engineering. It's 3/5 of a mile long, and pitch black. We walk along the towpath, where mules once pulled barges up and down the C&O Canal. It's nice and cool in there, like a cave.

5:10pm: We load up in the vans and depart the Paw Paw Tunnel. It takes a full two hours to drive back to Annandale, so we get rolling. We cross West Virginia, and then work our way east across Virginia. Several students nod off, while others discuss geology and travel along the way.

7:12pm: We return to the Annandale campus. Adios, estudiantes! The NSF crowd (Michelle and Nicole) and I retire to the Auld Shebeen in Fairfax for some Boddington's and Gaelic tunes. It's been a long day; we've covered a lot of ground and seen some cool stuff. Time for a pint!

As with yesterday's post, all photos are by Nicole LaDue, NSF. Thanks, Nicole!
Videos are courtesy of Amy Bertsch and Dean Kauffmann.

Labels: field trips, maryland, stratigraphy, structure, teaching, valley and ridge

Saturday morning, 6am: I roll out of bed and check the weather. Storms forecast for Hancock, Maryland, where I'm due to be leading a field trip that day. Hmmm. But based on the radar animation, it looks like they're going to hit hard from 10-11am or so, and then ease off for a bit before hitting hard again later in the day.

6:15am: Making coffee, with Lola the cat underfoot. I check the weather again, and convince myself that the timing of the rain will work for our trip's timetable. I decide to go for it.

7:00am: I call Dale Shelton (of the Maryland Geologic Survey) at home and confirm that it's okay if we go out on the outcrop if it's merely wet, but we can't go out if it's actively raining.

7:15am: I e-mail the students, confirming that the trip is a 'go.'

8:15am: "Bye, Lola!" I leave DC and drive out to Annandale. Once on campus, I gather up a few items (first aid kit, whiteboard, topographic maps), and then go out to the parking lot where students are gathering.

9:00am: We depart campus and head northwest.

9:45am: We leave the Piedmont and cross into the Blue Ridge province.

10:03am: We leave the Blue Ridge province and cross into the Valley and Ridge province (though there are a number of Marylanders who persist in calling it the "Ridge and Valley").

10:15am: The rain hits, hard. Windshield wipers on. Behind the wheel, I grimace. Hope it passes...

10:56am: We pull in to the Sideling Hill Visitor Center. Other cars containing other students are there already. We meet up and head indoors.

Sideling Hill is a massive roadcut in western Maryland. If you've ever seen it, you'd remember it. I won't go into all the geological details here, because (due to the rain) we didn't see them all. But if you're interested, you can read in more detail about Sideling Hill on my website. Long story short: We've got some early Mississippian strata here, derived from the weathering of the Acadian highlands to the east, deposited at the edge of the Kaskaskia epeiric sea. Then they were folded up during Alleghenian mountain-building.

12:00pm: After reviewing some of the salient details inside the Visitors Center where it was warm and dry, we ventured out into the rain and wind. Fortunately, a pedestrian walkway over the highway gave us a decent vantage:





Even from this limited vantage, we are able to observe and interpret some interesting features. For instance, check out the differential weathering of the shale vs. sandstone layers here on the eastern side of the outcrop. We likened this to other examples of differential weathering, like at Monument Valley, Arizona.



We also got a good view of what an oxbow lake looks like when viewed in cross-section. Note how this paleo-channel cuts into the layers beneath it, and is filled with a plug of dark shale, indicating low-energy, low-oxygen conditions.



2:00pm: After giving up on our chances to get out on the first berm of the outcrop, we depart the Sideling Hill Visitor Center, but pull over a short distance down the road to examine the diamictite on the western side of the roadcut. In drizzle, and shouting over the traffic, we discuss the multiple origins of diamictites:



2:10pm: On the road again, headed for our second destination, the Paw Paw Bends...

(More on that tomorrow)

All photos by Nicole LaDue, NSF. Thanks, Nicole!

Labels: field trips, maryland, stratigraphy, structure, valley and ridge

A couple of weeks back, out in the Shenandoah Valley, I pulled over to show some students the Oranda Formation (a limey shale which was transitional between Sauk sedimentation and the clastic influence of Taconian mountain-building). But in the midst of my arm-waving, an object caught my eye. On the ground amongst umpteen gazillion slabs of shale was this thing:

What is it? Any ideas? Because I was on a geology field trip, I thought, what kind of fossil is that??? but now I don't think it's a fossil. The grid is too regular, and it lacks a familiar biological symmetry. Could it be some part of a car? It was on the roadside, after all. Each of the little grid squares is 1mm on each side. Here's the side of the object:

You can see the long square-cross-sectioned tubes are bounded by a "shell" of some sort. This "shell" is about 0.5 mm thick. The arc of that curving "shell" suggests it may once have been part of a larger cylindrical shape, with a diameter approximately the same as a 1-liter Nalgene bottle. Lastly, here's an image of the other side (opposite picture #2):

Now that looks like some sort of biological encrustation -- but could it just be slag? There's definitely bubble-like features. My current suspicion is that this is some automobile part that got too hot. This bubbly mess in photo #3 suggests it melted down, perhaps causing the owner to pitch it on the roadside. That sort of waste disposal happens a fair bit in Virginia.

Any ideas what this thing is? Thanks.

Labels: field trips, unknowns

Cleaning up my hard drive today, before switching over to the laptop for my summer travels. Thought I would share a few annotated photos from my "Geology of Glacier National Park and surrounding areas" class that I took last summer.

Here's Chief Mountain:


On the trail to Firebrand Pass, here's the contact between the Altyn Formation (lowest of the Belt Supergroup exposed at Glacier) and the overlying Appekunny Formation:


The Purcell Sill is a readily recognizable feature high on the glacially-carved walls of Glacier National Park. This shot is from the trail on the way up to Grinnell Glacier:


Here's a shot from Sun River Canyon, showing one of the many imbricate thrust faults there, with some glacial till thrown in as a bonus feature:


Just outside of Sun River Canyon, we saw some nice recumbent drag folds on some thrust faults in the Cretaceous rocks:


This one was from early in the trip, on the road from Helena up north towards Glacier. Specifically, we stopped in Little Prickly Pear Canyon, near Wolf Creek, and saw these chevron folds in the Cretaceous rocks there:


Along those same lines (folded Cretaceous strata), here's a gorgeous fold just outside the park's boundary, on the road leading north from Two Medicine towards Many Glacier:


No annotations on this one, but I wanted to share it anyhow: a blind thrust / drag fold complex, in the Grinnell Formation (exposed on the trail up to Grinnell Glacier):


Lastly, some snow photos. I took this shot on my way up the trail to Grinnell Glacier, because the holes in the snow reminded me of the scary mask face from the Scream movies. But then on the way down, I realized I had the opportunity to document how much snowmelt occurs in six hours of Glacier NP summer weather. Hence, the bottom "after" shot:


That's it for today... Enjoy!

Labels: field trips, montana, msse, plutons, proterozoic, sediment, structure

On Saturday, I took a group of NOVA summer school students to Shenandoah National Park to look at some rocks. We had great weather, and saw evidence of Grenvillian mountain building, the breakup of Rodinia, and the transgression of the Sauk Sea. A real crowd-pleaser was an outcrop of what was once columnar basalt (the Catoctin Formation). I say "was once" because the basalt has been metamorphosed to greenstone, and the columns have been squashed into more lathe-like shapes.

Here's a few photos of the columns:

All four photos by Nicole LaDue (NSF). Thanks Nicole!

Labels: blue ridge, field trips, primary structures, shenandoah, teaching

Yesterday, I took my Audubon Society / USDA Grad School "Natural History Field Studies" students on a field trip to examine the bedrock geology of Washington, DC. We had a good time: beautiful weather, great attitudes, and even luck with parking! I guess because it's Memorial Day weekend, a lot of people have left town. One of the great challenges of urban geologizing is finding room for those infernal cars...

Here's a photo of the group at Chain Bridge, DC, on Sunday morning:

That class ends on Monday night, bridging the gap between my NOVA spring and summer semesters. It's been a good run -- thanks, folks!

Labels: dc, field trips, piedmont, teaching

Hoo boy! A busy trio of days for me. Thursday and Friday were devoted to an intensive 16-hour Wilderness First Aid training course (WFA). And today I led a twelve-hour field trip to Shenandoah National Park.

As you may recall, I got a grant to cover the tuition for six instructors (four from NOVA, two from Thomas Nelson Community College in Hampton, VA) to get WFA Training. Because he is totally cool, my dean also threw in $500 to cover an additional two instructors from our division on the NOVA-Annandale campus.

So, thanks to the grant and my dean's add-on, eight people who lead field trips for the Virginia Community College System got free Wilderness First Aid training! I'm pretty excited about that. Now, I think we stand a much better chance of saving a student's life if something were to go wrong on a trip.

The training was pretty intensive. Nancy Chamberlain of our Parks & Recreation program organized the event (assisted by geology student Quinn F.), and kept us well fed. The training itself was provided by Wilderness Medical Associates. They did a great job.

Here's the crew:

From left to right, that's Victor Zabielski (NOVA-Alexandria), Beth Doyle (NOVA-Alexandria & Annandale), Jen Martin (TNCC), Erik Burtis (NOVA-Woodbridge), Pete Berquist (TNCC), Ken Rasmussen (NOVA-Annandale), me (NOVA-Annandale), and Kirk Goolsby (NOVA-Annandale).

Pete and I are both products of the undergraduate geology program at William & Mary, he in 2001, and I in 1996. Here, Pete splints my simulated "broken leg":

(That's the way we are down at William & Mary. We help each other out.)

Do you lead field trips? Do you know what to do if a student breaks a leg? ...or goes into anaphylactic shock? ...or gets a stick through their eyeball? I'm sure glad I have answers to these questions now, and would recommend this (or more?) medical training to anyone who takes students more than 2 hours away from professional medical help. There's some serious @#%* that can go down in the backcountry. I feel like field trip leaders have an obligation to get trained in how to handle that @#%*.

Labels: conferences, field trips, grants

Today, some shots from my time in Yellowstone National Park last summer. Here's Mammoth Hot Springs:

Close-up of the travertine deposits at Mammoth:

Me advertising my brother's company at Mammoth:

Norris Geyser Basin, slime:

Norris Geyser Basin's loneliest tree:

More slime, this time two colors:

Nasty patch of slime. Looks like snot:

Bison herd:

Columnar jointing in basalt:

Me showing you where the columnar jointing is. (I'm pointing at it...)

Strata exposed in the Tower area:

And here they are again, labelled:

Lastly, heading north out of Yellowstone back to I-90 and Bozeman, here's a weathered-out Eocene dike in the Paradise Valley. The dike is more resistant to weathering than the rock it cuts through, so it stands up as a "wall"-looking feature.

Labels: basalt, field trips, hot springs, limestone, montana, primary structures, stratigraphy, travel, yellowstone

Here's a few more photos from the recent field trip to the Massanutten Synclinorium in the northern Shenandoah Valley, Virginia.

Some more Arthrophycus (?) trace fossils in the Massanutten Formation:

Outcrop of the Massanutten Formation on Route 678, south of Waterlick, VA. Note that the bedding is dipping to the south (reflecting the overall "canoe"-shape to the structure of the Massanutten Synclinorium... this is the "bow" of the canoe...):

Shelly horizon in the Mahantango Formation. Mainly brachiopod debris, but also crinoid columnals:

Cross-bedding in the Martinsburg Formation's Bouma sequences. This is a sample I collected on Saturday. I sawed it open on Monday, then polished it and gave it a coat of clear acrylic. Sample length is about 5 cm:

Ditto. As above, we can see clear cross-bedding here, reflecting current flow in these ancient turbidites:

Bedding / cleavage relationships expressed at an instructive outcrop in the parking lot of a pet store north of Front Royal, Virginia. Bedding is clearly visible running subhorizontally across the picture, but the rock breaks vertically: a tectonically-induced cleavage:

You could hardly ask for a better outcrop to teach bedding / cleavage relationships. Here's a medium-sized anticline in the same outcrop (note quarter, center, for scale). It clearly displays a fan of cleavage orientations. Lovely!

Lastly, on that same note, here's a sample I collected fromthat locality, with bedding planes and cleavage planes highlighted through the magic of CorelDraw. The stripes you see on the face of the sample are formed by the intersection of bedding and cleavage planes, shown schematically in red:

Labels: appalachians, field trips, fossils, primary structures, valley and ridge, virginia

Here's another transcript of one of my field trips, again from uber-dedicated student Jill.

--- T R A N S C R I P T --- B E G I N S ---

Prince William Forest Park - Field Notes
Hike April 6, 2008
Paper due: Sunday, April 20th

Transcription Note - I apologize for the lack of words, at times. We were so near the river, the background noise of the river made it difficult to transcribe. Also, it rained during the morning. It was not the best day for a hike, but the weather outsmarted all of us that weekend.

Valley - Quantico Creek - Main Creek
South Fork - Main Tributary

(Tape #2?)

Field Notes - Weather: Raining...Callan cautions us about being nice to one another in the rain...

On Trail Observation - Top of high hill - rounded river gravel mixed in with sand & clay

On top of another hill - we will talk about it.

Volcano erupting signage. - Hawaiian volcano example. What it would have looked like 500 million years ago. Chain of volcanic offshore islands spewing out lava. As time goes by subduction is bringing those to the edge of North America until they eventually collide. Then all igneous rock - basalt rock gets slathered onto the edge of North America. Ex. - A snowball. New basalt rock is packed onto the edges - younger material added onto the edges.

Continents (low in density 2.7) never subduct. Oceanic crust subducts (2.9 vs. 2.7). Whenever the two butt heads, oceanic crust loses. Result is isotopically dated rocks which make up the continents and ocean floor. Ages are wildly different - 4000 million years (rocks which make up the continents) vs. 200 million year old (ocean floor). There is a huge difference. Continents are 40 times as old as the oceans.

Oceanic crust is constantly getting destroyed vs. continental crust which is constantly getting preserved.

Oldest rock is in the Northwest Territory of Canada.

Old Rag mountain. Rock from Old Rag is 1 Billion years old. 1 Page handouts. 1st event - Grenville Orogeny intruded granites into the crust. Granites are a symptom of mountain belts/building. And the granites cooled and became Old Rag. The Iapetus Ocean Basin was opened up. Cracks opened up into that granite into which mafic igneous rock (basalt) squirted into those cracks. Hiking up Old Rag - narrow little slots - which are those cracks. Floor is made up of dark colored, fine grained rock whereas the sides are coarse grained, light colored granite.

All that transpired before the stuff we are talking about today.

Volcanic rock is underneath us. We eventually will see it. First we will see sediments that accumulated at the bottom of the Iapetus Ocean right next to the volcanoes. Then at lunch today we will see some of this volcanic rock, itself.

We will get to see the rocks that made up volcanic islands.

We are at the boundary of sediments and the island arc further east.

Stop - signage. Small lake, dammed valley Sign about the Fall Line. 2 Virginia physiographic provinces meet. Region of the 1) Piedmont 2) Coastal Plain (as day goes by)

Boundary is the Fall Line. Coastal Plain is made out of very loose sediments, not stuck together in to a rock; loose gravel, loose sand, loose mud. Therefore, it is very easy to erode away. It is easy for water to strip it away.

Whereas the Piedmont is made out of hard rocks. (Like the ones we are gong to spend most of the day looking at). As water is draining from the Appalachian Mountains in the Atlantic Ocean, it is easy to strip away coastal rock and hard to strip away the Piedmont Rock. And, as a consequence, the boundary between the two you tend to get rapids and waterfalls. Those rapids and waterfalls line up on a line from Southwest towards Northeast - we call that line the Fall Line.

Here is the fall zone. The image on the left is a Geologic Map. You can see the difference in colors along the water. Coastal Plain layers vs Piedmont Plain layers. The Coastal Plain is draped on top of the Piedmont like a blanket. (see diagram). The deepest, therefore the oldest part of the Coastal Plain is a series of rounded river gravel. OK? Ring any bells? That is what we are looking at back there...these gravels. So, that is actually part of the Coastal Plain draped on top of the Piedmont. Right here we only find it on tops of the highest hills, but as we head east, it is found at lower and lower elevations. So, what we are going to see as we get down at the bottom of the hill - we are going to see our first little waterfall. Where the water of the South Fork of Quantico Creek which is the creek that carves this valley here where that is falling over some of these hard, difficult to erode rocks. And, then as we get down into Dumfries this afternoon, we are going to move out on the Coastal Plain itself where it is going to be very flat and the rock layers are very easy to erode. It is going to look very different - and it is a major theme we are going to discuss more over the course of the day. Since the sign is here, I figure I had might as well say something about it.

Stop. Our first actual outcrop of rock. I wanted to give you guys a chance to check it out. Outcrops are where we actually get to see some of the Earth is rock formations at the surface - and - you would think they would be more common, but they really are not. One of the reasons for that is we are trying to do Geology in the East. Out West, there are no plants, so all the beautiful rocks are exposed with these ugly forests that cover up the beautiful rocks. So, you only get to see the rocks where the forests have been stripped away. Like here, where a stream has cut down to reveal the rocks or sometimes when we build a road underneath. So, on the East Coast we are largely limited to the rock exposures that are in creek bottoms or in road cuts. We are at the creek bottom of the South Fork Quantico Creek coming out of that little lake from the dam upstream there. I want you guys to take 2 minutes. What you are going to do is examine them. I want you to make observations about this. I do not expect you to come up with the whole geologic history...

Little patches on the surface. Those are not rocks. Those are a symbiotic relationship between a fungus and an alga, right here where it is wet. Go.

So, yes. Yes, what is causing that? Something? The water. When these outcrops are first revealed they have nice angular edges like over here next to David. As the river flows over them with time they get worn down so they get nice and smooth. We will see some really cool smoothing out features downstream like the one, Kathy, you were noticing on that sign. Yeah, we will see some of that later on. Uh, Tee, what did you notice? OK, little sharp edges...OK...breaking...everything is parallel. We see this parallelism in the rock and that extends out to the stream making these little ridges of rock that extend out to the stream... (We will get to that - hold that thought). First, I want to talk about this parallelism that we are looking at here. Jill, what are we looking at here? Foliation. Right. Folio comes from the Greek word for plant or leaf - leaves on trees...(two choppers overhead go by...)

Foliation - originally folios to describe leaves and then eventually used to describe paper or books (a foliated structure...pages in a book parallel to one another is what we are seeing here in the rock). Something layered. What is it that is layered in the rock? Sediments from the breaking down of those mountains? Let us back up. You are right, but I want to make it a little bit simpler. What are rocks made out of? Minerals, right. What we are seeing here is the minerals all lined up in a certain direction. What force could line those minerals up? Pressure from what? A tectonic collision. The North American Continent pushing in this direction and the volcanic islands pushing in this direction. Let us go back to this idea of these two plates colliding - one is a volcanic island arc and one is the North American continent squishing together - this stuff got caught between - a sick analogy...a cute, little fuzzy kitten chasing a butterfly out in the meadow. Then it runs out into traffic on Route 66 and a big Mack truck comes along from one direction and a cement mixer comes from another direction and they collide head on and the kitten gets caught I the middle. The kitten changes its shape as a result of that collision - the kitten starts off with little kitten bones and fur all oriented in different directions, and as the two trucks collide, the bones get aligned perpendicular to the two trucks' collision direction. This is the mangled corpse of these sediments of /in the Iapetus Ocean. They have been crushed. They start off in all types of different directions. I will use my hands to represent two different directions - and then they rotate to the only stable configuration possible. Picture a bunch of papers on your desk. Push your hands toward each other and the papers end up lining upright the closer you put your hands together. The minerals here are all upright - all standing up essentially vertical that is..............See how straight this thing is? (A rock used as an example).

Break...then...

...bubble. OK. Did you guys see that in the back? OK, say again, speak up... "...crack in the rock and water filled in it, warm water and it crystallized into quartz." Right, and how do you know it was deposited by water? What is the clue that is telling you that? Hydrothermally deposited quartz. This white color is due to little tiny bubbles of water in that quartz mineral crystal. That is a sure indicator that that was originally deposited in a crack. Now, however, it is only the little chunk, just like that; then there is another little chunk there and another one there and there and there... They are a little bit pink because they have been stained by rust. Notice how they all line up in the same direction, too. Like this thing here is 7 cm wide by 40 cm long. Compression coming in East to West making everything line up North to South. Now, let us talk about the original sediments that got crushed here. (The so-called kitten). There are three rocks here in my hand; three different sandstones. 1) White quartz sandstone, 2) pinkish arkose (potassium feldspar) 3) greywacke - gray - all made of sand. This one is exclusively quartz. This one is a mix of minerals and has lots of potassium feldspar. Greywacke is a mix of sand and mud. It is a dark, gray color (clay as well). If I asked you to pick one of these three as the original source of these rocks before they got squished, which would you pick? Greywacke. See the color? If I put these three down, the one that blends in the most is the gray one, right? Now there are some other things influencing the color here, but yeah, if you zoom in on these rocks you will notice little grains which were originally sand and mud in this ancient, dead ocean - The Iapetus Ocean. When the tectonic collision happened, a lot of the mud reacted, becoming mica. Mica is another mineral, and a defining characteristic of mica is sheets; flaky sheets lining up one way once again indicating again that squeezing direction.

Zeta (sp?) was asking about some fractures cutting across, like here. See the fractures? There are a bunch of brittle features cutting across this rock. These rocks were squished in a flowing way and then later they were broken by brittle fractures. So, these brittle fractures may be related to the uplift of these rocks, over time. I do not know, or cannot say specifically if it is related to some tectonic cause.

But we know (with certainty) that that happened after the rocks had cooled down again. During mountain building, these rocks were hot and flowing. After mountain building, they cooled down and that is when they broke. To get these rocks to flow, they would have had to have been heated up to 350 degrees Celsius or so. Maybe higher. We will see evidence down the way of partial melting of these rocks. Partial melting yields granite magma. So, that is another symptom of mountain building. So, you have to get the rock up to 450 degrees Fahrenheit (when wet) in order to get it to melt. Using the Principle of Uniformitarianism, you can say they once were molten based upon how we know such rocks form today.

Greywacke. David - greywacke is from Old German for grey rock.

Making the distinction between a sedimentary rock and metamorphosed sedimentary rock...layers of sediment. You do not end up finding these big, long flaky bands of quartz...presence of all this mica. We do not get big deposits out there in the actual world where mica accumulates in big layers. We get layers of mud. So, the mica itself is a metamorphic mineral. Also, we do not see any continuity. As we look along the way here, we do not see that we can detect one layer of coarse grains or one layer of sand, mud, or anything like that. Instead, we see a sort of smeared-out looking feature. These rocks appear smooshed. What would you add to that, David? (The mica here is the metamorphic mineral, not a sedimentary mineral...B word....boudinage...)

Boudinage. French for sausage. Describe a rock layer that has been broken into sausage like segments. Right here, look at this you guys. 1,2,3,4,5 sausage links. This quartz vein is broken (as a brittle phenomenon). Also, the flow was pinched out along the breaks. There are pinched out ends, like a string of sausages all in a row. This occurs at 10-15km depth from crust...right at the transition between brittle behavior in the upper crust where rocks break, and more flowing behavior in the lower crust. Brittle means breaking. Flowing is like silly putty or bread dough.

So, I wanted to elaborate on something. See picture...4 parts. Something we can deduce about these rocks. A preserved sedimentary structure called graded bedding: layers of rocks that are coarse at the bottom and fine at the top. No graded beds here today, but at the Billy Goat Trail, you will see graded beds. That tells you how these sediments initially accumulated. I am correlating these rocks here with the rocks at the Billy Goat Trail, based on similarities in their mineral content, and my knowledge of the area. I'm saying these rocks exhibit all characteristics of Billy Goat Trail rocks except we do not see any graded beds preserved here. In the Billy Goat Trail, there are a few lucky areas where we see graded bedding preserved. Why do I care about graded beds? Graded beds are deposited by currents flowing along at the bottom of the ocean. (Picture of turbidity currents). These currents are very dense, sediment rich flows, that go along the bottoms and they slow down. As they slow down, all the sediments caught up in the rolled up water settled out. The stuff that settles out first is the big stuff. The stuff that settles out last is the light weight, really fine-grained stuff. So, you end up getting these graded beds forming. Those formed down in a location like this, down in the deep sea in what we call an abyssal fan or a submarine fan, where sediments are coming off some land mass piling up in the deep sea making graded beds of greywacke. Again, greywacke means nothing more than a mix of sand and dark mud. So, that is what this used to be. Then it got crushed up. When did it get crushed up? When the Iapetus was closing, good. As the Iapetus was closing (let me pull out another graphic here) it was a scraping up all that sediment. OK, the subduction zone was going down the hatch, but the sediment on top of the oceanic crust was getting scraped off. It was building up into a big pile; a big, jumbled pile of sediment. That is analogous to a bulldozer moving over the ground scraping up a big pile of dirt in front of it, OK? Where the bulldozer is like the island arc, and then in front of the continents are the sediments it is scraping up. OK? So, that is what we are on here. Really, these rocks here are the big pile of muck that got scraped off the subducted plate and then later it got squeezed between the islands and North America. So, we call this big pile an accretionary wedge. Now, Dean, you were talking earlier about California and San Francisco. San Francisco is still on an accretionary wedge. The difference between Prince William Forest Park and San Francisco is, Prince William Forest Park then had that accretionary wedge caught between two continents; Africa and North America, and it squished. Whereas San Francisco, it just filled out. It has not been squished between two continents, yet. Give it another 50-70 million years, something like that. OK. Questions? (Why the silt...? C. - What silt are you observing? Does that just look like it is going into the hills?) What was stable in the middle of the mountain belt is no longer stable. The mica is rotting away. In fact that is why over here, when I was running my fingernail through these little grooves, there is a groove there to run my fingernail through. The mica is soft and it rots away really easily, so it ends up etching out. And, the quartz is very stable and so it does not erode away easily and that is why it makes these little ridges. So, guys if you have not felt this for yourself, come put your finger on the rock and feel this yourself. That is why, like, on the drive down I was noticing these big white boulders on the drive in. Those big, white boulders are made of quartz - it is stable. It does not break down over time. That is why when you go to the beach; the beach is made out of quartz sand. It is not made out of feldspar sand, mica sand or anything like that. It is quartz. Quartz is the stuff that lasts. (Student questions Callan. C. -- Yeah, right. Black beaches are where you are really very, very close to a basalt source. And, there are not...there is not ....adequate time to break down all those unstable minerals, so the beaches built up making those black minerals there. So, we are finding that there are some black minerals even on beaches here on the East Coast, but, the majority of it, when it is a nice mature beach, is quartz sand.)

One of the exercises I had Jill do this semester, and I had Dave do last semester, as well as the rest of my Physical Geology class is that I give them a little, bite-sized Snickers bar and they have to suck on this Snickers bar. The chocolate dissolves away very readily in their mouths followed by the caramel. The nougat lasts about 10 minutes or so. But even after you suck on this thing for about half an hour, the peanuts are still there. Peanuts do not dissolve, right. Peanuts are like quartz whereas all the other ingredients in the Snickers are more like other less stable minerals.

(Student talking about some observation). C.- Actually that is a great observation. Let us take that one step further. Imagine, now this creek here is not a creek but a road and you are driving down it. You take this turn and you take it a little too fast. Which way does your body get pulled? Right, towards the outside of the curve. So, basically, during flood times the creek comes in and slams into that wall right there and strips away the plants and strips away the leaves and strips away the dirt and it exposes rock there. Whereas the rock that is underneath the hill here is not getting hit head-on by the force of that creek. So, it fills up with sand, dirt, and leaves over time. I did hold this rock down here and I just wanted to point something out, it is a little bit difficult to see because the stupid thing is all wet, alright, just like us. But, this is a foliated metamorphic rock. Does everyone see the plane of foliation? So, if I were to line it up here with the regional foliation, it would look like that. Alright, but this one is loose so we can pick it up and examine the plane of foliation itself. And, there are little black needles there on the surface. Do you see those little needle-like minerals? They are needle-like mineral growths. Do you guys see them there? It is almost like if somebody took a bunch of chopsticks and dropped them on a desktop. The chopsticks were in this random orientation because they would be parallel to the surface of the desktop. OK? If I took all your pens and dropped them on top of someone's notebook, they would all splay out on top of that notebook but some might be pointing this way and some might be pointing that way. That is what you are seeing here in this plane of foliation. These are amphibole minerals. And the amphiboles are randomly oriented within the plane of foliation. Pass it around. I know David wants to get a good look at that with his lens. Make sure he gets that. Great. Good. (David and Callan have discussion about amphibole, spelling, etc...David asks, does the random orientation of the amphibole suggest that was it done when the pressure has been released. C. - No, I think basically that what we have here is we have flattening. Remember what we talked about was the different types of deformation; folding, faulting, and I think I said squeezing or flattening. These rocks have been flattened. And what we see is that the dominant pressure direction was coming this way and then the rocks, in order to accommodate that (here we go – here is my little Nerf ball. Yeah, I left my kitten at home...) Um, they are getting squished in this direction. Right now the Nerf ball ends up basically elongating outward this direction and growing in this direction, as well. So, like, you think about three dimensions, these right here are growing and this one...whhish....gets squashed. So, I think what is happening here is that flattening stress is causing the amphibole as they are growing...they ca not grow in this direction. It is like, try growing if the building collapsed on top of you. But, you can grow in this direction.)...we will see a couple of them here today. ...Dave, unfortunately it is not...it takes certain elements to make the amphibole, so unless those elements are present in the original sediments, you do not make it. Dave - OK. Student - Do you want to leave this here? C. Yeah, that is why I brought it down. C. - No, I would not break it, I would just kind of stash it over there underneath a tree or something so maybe in a year from now I can find it.

Another segment...

...you take away the fact that we have determined that these used to be sediments in the Iapetus Ocean basin, and then they got squeezed due to mountain building. Due to that Taconian Orogeny...this episode of mountain building that we mentioned back in the shelter. Taconian stands for the Taconic Mountains of New York, alright. (see the one page handout that I gave you). Dave - What are the compass directions here? C. - Essentially, North/South and then, East/West - squishing. Now is it actually that? Well, no its North/Northeast, but close enough. Dave - it is a good observation to make in the paper the direction in which the squishing seemed to happen. C. - Yeah, I would say that would be a great observation to make in the paper. Um - it may not have been originally in that direction though, because remember a later collision happened. That later collision also squished. So, it is like remember the kitten, Mac truck, cement mixer pile-up we had earlier? Then along comes a tank and crashes into it, OK? And then that ends up rearranging everything again. Dave - could the magnetic poles have changed here? C. - Uh, yeah, but we have no magnetic signature in these rocks. We are just trying to get in our head how - Dave - You did say North and South...C. - Yeah, so we are using modern day directions but then again North America would have been rotated around in a different position, so it is a complicated question. Sounds like it is a simple question but it is really not! Another student asks a question. C. - You do not have to understand about magnetic poles to understand what we are talking about...Dave - ...unless it is present day...(Callan brings discussion back around to)...yeah, that is all we have to work with and that is what is going to be most readily available to you guys. So, again, the one thing to think is this foliation essentially lines up on the same line from the Appalachians, basically from Georgia...Dave - OK, yeah, that is a better way to go, yeah. C. -....so, that, that is due to this first collision...Dave - ...Appalachians...to the ocean, like that? The Appalachians have...to the Ocean, like that? C. - Well, the Appalachians would be parallel to this. So, essentially we are looking at Maine up that way, Georgia down that way...ok, West Virginia, that way, and then the Atlantic out this way. Uh, I was in the middle of making a statement there and I got derailed.

(Dave - If these clay minerals had all been aligned and micas formed in the first compression, and they were tilted up in whatever orientation, and a second collision took place and it came from a different angle, would all this seem likely to get reoriented or would it preserve some of the old orientation? C. - Probably you would have some preservation and some would get reoriented, depending on where you have little bits that poked out, those being more susceptible to being re-rotated.) Um, that being said the overall structural grain of the Appalachians is this North/Northeast to South/Southwest direction, so, I mean I think we can just sort of simplify things - well, it may be an oversimplification - we can simplify things by saying these collisions all essentially came in one after another from the same direction. First, these volcanic islands during the Taconian Orogeny. There was a second collision that happened, later on, we are not really going to talk about that today - called the Acadian Orogeny. And then finally, Africa hit and that was the Alleghanian Orogeny. So, all these different orogenies were episodes of mountain building.

Oh, I know what it was that I was going to ask! When does the Taconian Orogeny happen? Well, Dana, that is just great. How did you know that!? She says 460 million years ago is when this actual collision took place. And, she is right, but, she is just pulling that number out of thin air. You can not see it. Student - she got it out of the papers C. - OK? Yeah, you are on the right track. OK, radioactive decay. So, certain minerals when they form, they take in radioactive isotopes, and then if you can go and you can say that that mineral is a mineral that only formed during an orogenies, then you can say, "Ah ha!" All you have to do is look at the radioactive isotopes that remain in that mineral and compare it to what they decay into. So, in this case the mica here has been isotopically dated. What they did was they looked at radioactive potassium 40 that is present in that mica and they compared it to the daughter product - the stable daughter which is called argon 40 And, the mica as we said earlier formed during metamorphism ...was a good state for the orogeny. The date is 460 million years ago. We are going to see a granite today, and the granite has a date of 464 million years ago. OK, so it is basically the same age. And it tells us about the same event, and granites, you remember, are another symptom of mountain building. So, we have got a really good view on the orogenies then by dating these two independent, isotopic systems. The metamorphic mica here, and then the granite that resulted from partial melting. I will remind you of that again when we get to the granite, OK? Alright, that is a good point to keep in mind. Student - So what overall type of rock is......C. - No, this is not granite, granite is much lighter color and granite does not have this foliation. Um - so this is a metagraywacke. All right. Meta, the prefix meaning change, and, greywacke telling you what it originally was.

OK., I know everybody is hungry, so we are going to hoof it. We are going to walk down to the Cabin Branch Pyrite Mine. We are going to be walking across and along the South Branch of...

...stop and maybe point out this point bar......do not feel like you have to take notes. OK, I’m not going to go over anything really important...


(Tape #3) After lunch...

OK, so granite you remember is produced by the partial melting of other rocks - remember I showed you that other diagram where you had a bunch of starting minerals and then the light colored ones sweated out - they melted? Whereas the dark colored ones stayed behind. So, here, it is a metagraywacke that is being partially melted. And the minerals that are easiest to melt those metagraywacke are quartz, feldspar, and mica - some of those are basically melting out and they are leaving behind the darker colored minerals. Ok, so we are producing these granite blobs and these blobs of magma are moving up to the crust and eventually they are settling down and crystallizing into granite. Remember we call these blobs plutons. So, here in this diagram which is part of your handout, I have got a diagram showing you some igneous plutons, OK? So that bodies that were magma and have crystallized into solid igneous rock, like a granite - OK, here is one pluton, here is another pluton - they cooled underground. Now, basically these plutons are these wet batches of magma and they are moving up through the crust. What happens to the pressure that is on them the higher up they go? Yeah, it is released and as a result they erupt - basically the granite separates out and the stuff that is most readily removed leaves the granite. So, think about a bottle of soda - did anyone bring a carbonated soda? David did. David brought a ginger ale. So, when he popped the top on that, OK, it started off as just liquid, but when he popped the top he released the pressure on the liquid inside. And as a consequence, a gas that was dissolved in the soda came bubbling out. Carbon dioxide came bubbling out of the solution. The same thing is happening to this granite which, remember, originally was magma. As it gets up to shallower depths in the crust, gases and things start coming out of it. It is leaking fluids into the surrounding rock. OK, so it is intruding into this rock and so these fluids and gases are penetrating the surrounding rock. Some of those fluids and gases would probably be water vapor, another one would be carbon dioxide, another one would be hydrogen sulfide, um a bunch of different fluids, OK? And one of the things that these fluids are taking - with - them, (I think I have got my mouth.../sandwich repeat) - OK, the fluids are carrying with them metals. Alright, metals readily dissolve in those fluids that are carried out of the granite by the fluids. And as those fluids penetrate the surrounding rock, they cool down and the metals are deposited there. Frequently, the metals are - they glom onto sulfur. Sulfur joins up with lots of different metals and then it settles out in this big sulfide deposit which surrounds the granite pluton. OK? So, it is kind of like a halo or an aura surrounding the pluton is this big aura of sulfides deposits - sulfur mixed with metals. OK? So, some sulfide minerals contain galena, some of you are familiar with galena, it is beautiful, it is got this silver luster, and these little cubes. Um, another really important one is pyrite. Pyrite is nothing more than iron sulfide. The chemical formula for iron is Fe - the chemical for pyrite is Fe. OK, it is nothing more than iron mixed up with 2 sulfurs. For every one atom of iron, there are two sulfurs bonded to it. And that makes this mineral called pyrite. Then, what color is pyrite? Golden. Yeah it is sort of this golden color and it looks a lot like gold, if you do not know what gold looks like. Um, it is got that same golden luster. Well, they were mining this pyrite here. We have already said it is not gold so why are they mining it? What on earth is the point of pulling up fool's gold from the ground? Gunpowder. C. - Gunpowder. So, basically, they are not interested in iron, they are interested in the sulfur. The main thing they are using the sulfur for is gunpowder. It is also used in many other industrial applications like making soap and refining glass and other things like that. But, not nearly as exciting as warfare. Jill - Civil War? C. - The pyrite mine right here actually started in the aftermath of the civil war, and then it actually hit a fever pitch during WWI, when there was a really big demand for gunpowder. So, they were pulling lots and lots of pyrite out of this mine, processing it to extract the sulfur and then using it to make gunpowder. So, geologically why there is a mine here is that the granite is essentially sweating out all these fluids. The fluids are rich in dissolved metals. It is just like when you sweat, there is salt in your sweat. And if it dries out on your shirt, you get a little white crust left behind on your shirt, right? So it is the same thing her except for instead of salt crustiness left behind, you will see a metal crust. So, the same granites that were produced during the Taconian Orogeny were sweating out these deposits of pyrite into the crust. Later on, people came along and said, "Hey, we can make use of that, let's make a mine here. We will dig into the hills and dig out as much pyrite as we can." So where we are right now is we are sort of geologically on this dome surrounding one of theses plutons, OK, we are in this sweaty armpit region. So, what I want to do now, is I want to go and find some pyrite and look at it. So, what we are going to do is walk back over here to this area where there was nothing growing. And, we are going to go look for some pyrite. Does that sound workable? Eventually we will come back to this place, so if there is something heavy you do not want to carry, you can leave it here and then come back and pick it up again. (Student question - inaudible. C. - The granite pluton was. Yeah, so the granite - the body of magma which would eventually cool into a granite. We will visit that granite this afternoon). (Student - So it is coming out because it...C. - the granite was, yeah, and as it is getting to shallower depths in the crust, it is devolatilizing, so the various gases that are dissolved in it are coming out. So, it is starting off here during partial melting, then the granite is organizing itself into these blobs, they rise through the crust, as it rises it is sweating out into the surrounding rock all these mineral deposits. Alright, sometimes as it moves into the crust, the crust cracks open and you end up getting veins of pyrite or veins of hydrothermal quartz. Some of those veins of hydrothermal quartz have gold in them, actual real gold. Including in the northwestern corner of this park, and by the Billy Goat Trail in the Great Falls area. So, there are gold bearing quartz veins in this area and they are coming from the same source. They are essentially being sweated out of this granitic magma. (Student - ...keep that in mind if the dollar keeps going down. C. - That is right, we will start mining our National Parks.) OK, other questions? Let's go.

(New Spot.) Now, I'm going to start talking now about some of the environmental damage that the mine caused. In this area, where the ground was near the mine operations, they were filtering the lower grade ore, you know the stuff that did not have enough pyrite in it, and they just kind of dumped it, alright? And, that is what we are sorting away here, right? And that pyrite is then soaking out here at the surface of the Earth in water, and that water is oxygenated water. And, those two ingredients end of completing a reaction of water, oxygen, and pyrite. Water, of course, is hydrogen and oxygen. Oxygen is just oxygen. And, pyrite is iron and sulfide. So, basically, after that reaction you end up getting iron mixed with oxygen and hydrogen which is rust (FeOOH) and sulfuric acid (H2So4). So, two things are being produced here due to the weathering of the pyrite; rust and sulfuric acid. Rust is what is making the soil so darn red right here. It is staining everything red. Look at David's boots right now - they are getting all soaked in this red mud. Alright, the other thing is sulfuric acid. What is the effect of sulfuric acid that you see right in this area? Basically, most plants cannot grow in super acidic soils; soils that are essentially drenched in sulfuric acid. As a consequence, nothing grew here for a really long period of time. It was basically a day of awakening - completely environmentally degraded. So, the ground was basically an empty wasteland and then the Parks said, "OK, we have got to clean up this mess." So, they took a series of steps to essentially reclaim the land. OK, this is something that frequently has to happen where they do mining - reclamation - basically making it look like a decent landscape again. And, what they did was they brought in a lot of limestone. Limestone is made out of calcite, and that reacts with acid. So, basically it is a buffer through the sulfuric acid. And, when they laid down all these limestones in the area, some of them are dissolving away as soon as they get set down. They are taking away some of that acid. It is kind of like Tums in the landscape - that is a great way to think about it? Did you have some Tums this morning? David - no. So, it is like Tums through the landscape and it is working better in some areas and not as well in other areas. It is not working so well right here. There is still a lot of sulfuric acid right here in this area which is why you can actually go and pick up rocks there. There are no plants growing out. That is thanks to the acid. Same as that little patch there at the end of the trail - there is nothing growing there. That is so weird for the East Coast to have an area where there are no plants growing. That tells you there is something seriously messed up with the soil underneath.

One of the things I would like you to do, is I would like to have you test the pH of the waterways. You might want to clean off your hands first, because the way you are going to be able to read this thing is to check the color of the paper. Alright, this is a little pH paper here. It is going to change different colors depending on the pH of the water you put it in. Now, you want to make sure you are putting it in relatively clean water otherwise you will get sediment on this which is going to give you a false reading. OK? So, I'm going to give everybody a little strip here. You can choose to test this water here, somebody should go test the water of the South Fork, and somebody should retain their strip so we can test the water of the Main Fork of Quantico Creek. OK, so we want to collect data at several different points, to several different iterations at each point, so we have reliance on the data and then we will share everything we get.

Everybody tests. OK, what do you have? 6! What do you got? (Everyone testing.)

Results 5 or 6 - somewhere between a 6 and a 5....slightly acidic. He just put it on his tongue and it is a 7. So, your tongue is pH neutral, which is a pretty good thing for your body. So, he has a reading of between 5-6 so that is just slightly below neutral, so this area is slightly acidic. That is not as acid as it once was, but it is more acid than just what regular old water would be which is 7. So, as the number gets lower in pH level, the more acidic. Higher is more alkaline. End of segment.

...sweating out of a granite pluton. Then the fact that this was mined for awhile for the purposes mainly of making gunpowder, and one of the elements that make up pyrite is sulfur, and then the breakdown of that sulfur at the conditions found at the surface of the Earth here; mixing it with water and oxygen, making rust and sulfuric acid, and then the Park surface had to treat the area by putting down essentially the geologic equivalent of Tums with limestone chips in order to get rid of the acidity. Oh, and another point that we could make here that the plants that actually are growing here are pine trees. These are acid tolerant plants. Their needles, themselves, are acidic. So, their needles are dropping - so look underneath those pine trees. You see the carpet of needles underneath, right? Those needles are essentially making that soil more acidic and that makes it harder for other plants to grow there, OK? They make a special kind of acid called a tannic acid. It is the same thing if you brew your tea for too long - it is a sort of bitter thing and it makes your stomach hurt. That is essentially what is going on over there with those trees. OK, let's move.

Testing pH at new location. (Dave - So are these the rocks that they dumped? C. - Yeah, so this is the ........that basically have water coming through them. The water is...)

OK, so I imagine we all do not want to stand here for too much longer. Did everyone see that vein of pyrite that Topher found? Time to work our way back to the path.

New location.

...C. - I'm going to turn upstream on Quantico Creek. (Jill - Confluence of Quantico Creek). We are going to look for a place to cross Quantico Creek. We want to be on the other side of it.

New location.

C. - I want to point out we are at the confluence here. So, here is the South Fork of Quantico Creek, which flows under the bridge we just walked over. Right, here coming into the main stream of Quantico Creek, the two merge right here (Jill - the confluence) and they flow downstream. Where we actually want to go is where there are a bunch of branches across the creek down there. It is probably only 200 yards from where we are right now. All right, but, unfortunately there is no great way to cross the creek right here. So, we have got to go upstream a ways, until we get to a good creek crossing. As far as a bridge and cross over. David, if you want you can wade across, but, I do not want to make every...

New location.

...flow. Where were these lava flows accumulating? Jill - Volcanoes. C. - Volcanoes, where were the volcanoes. Jill - the island arc. C. - Yeah, the chain of islands offshore, you remember, ancestral North America about 500 million years ago. Then, subduction narrowed the ocean basin between them, and eventually they got added on to the edge of North America. Now, how do I know these are lava flows? Great. Color, texture, and maybe the mineral content. Yeah, so there are some good color indicators here. What color is this greenstone? It is a very descriptive name - greenstone. It is probably in the Old German for - just kidding. So, greenstone is metamorphosed basalt. Remember basalt is what is coming out of the volcanoes today in Hawaii. (Student - asks question. C. - Well, we call it magma if it is below the surface and we call it lava if it is above the surface. Once the lava cools we have to give it a rock name. The typical name we use for the dark colored rock is basalt). Basalt is what made up the oceanic crust and what made up these volcanic islands. So, when the basalt gets metamorphosed it undergoes chemical reactions and those chemical reactions turn it green. The main green mineral here is called chlorite - it is basically a green mica. There is also epidote. Right here there is a pistachio colored mineral. You guys see that one? It is sort of a bright green? Filling in little veins over here? It is epidote. Alright, so basically, I know Topher is going to ask about this - the "take home message" is that these were once lava flows that got metamorphosed. How do we know that? The Principle of Uniformity. When you see lava flow that gets metamorphosed in the world today they change color into a green color. The reason is that they grow chlorite minerals and epidote. ....yeah, well there is some other stuff. Remember these have gotten squished. So, a lot of the original layering is lost. They are foliated. They are foliated and again it is that squishing effect. OK, I want you guys to come and look at these rocks here. There are little white circles in the rocks. Oh, see these white blobs here? OK, what is going on here is the same thing we were talking about earlier. When you release pressure on a lava, it causes gases to come out of solution. Just like when David opened his Canada Dry the bubbles formed. When lava erupts at the surface bubbles form in the lava and gases come out, right? If those bubbles do not pop before the lava sets up into rock they are preserved as little holes in the rock, like Swiss cheese. We call those vesicles. The vesicles have gotten filled in with mineral deposits. Those mineral deposits are known as amygdules. Amygdule is for the Latin for "almond." So, these were originally decided to look something like almonds - set in a piece of bread, like that. There are some really nice ones over here with mineral deposits. Generally the minerals that are filling them in are quartz, well Let us just say, quartz. David - something about popping. C. - ...if they do not pop, it leaves hole. Later on that hole could get filled in with a mineral deposit. This is important. The bubbles form as gases are coming out of lava, then some of those bubbles pop, we do not have any evidence of it. But, some of the bubbles do not pop and those bubbles get filled in later on with mineral deposits which make these little white blobs in the greenstone. And, notice that these little white blobs are not perfect spheres. Up here they appear kind of like this. Why is that? They got squished - like a little kitten's eyeball. That is due to that tectonic squishing. You can see that they are all basically squished like this line up at the plane of foliation. Alright, they lay exactly parallel to the plane of foliation. That is why the sphere became a pancake. So, they are little pancake shaped fossil gas bubbles from a lava flow. We call them amygdule because they got filled in with mineral deposits. If they were still empty holes, we would call them vesicles. ( ...you can see epidote down here in veins... come down here with David and you can see them.)

Barely audible due to noise from river. C - ...ancient volcano island rock... ...Chopawamsic....Dave and Callan in a lot of discussion about the volcanoes, flows, etc...evidence of it all...Callan sticks to history of Virginia....at one time you could have walked from Ohio to Morocco. Now those rocks were once sediments in the ocean deposited way down...

...discussion about potholes....barely audible. The role in carving it out. When water come flowing through here, there is a vortex of water. Filled with sand, silt, and it acts as liquid drill bits. Layers of quartz and mica, quartz and mica. Quartz stands out in high relief. Sand gets in there and preferentially eats away the mica. So, that is a pothole and potholes are one of the ways that streams are cutting down in areas of waterfall where they are adjusting from one level to another level. Alright, Let us go ahead and work our way back to the trail and we are going to start climbing uphill, towards the bathroom...

OK, so here we have another tree that is tipped over, and it has brought up a nice, fresh sample for us. We can see here more of that gravel that we saw when we first started on the trail today. This is not a rock. This has not been stuck together into a rock - it is just loose gravel...David - it is a root ball, right? C. - Yeah, it is a root ball of a tree. You can pick up the loose grains of sediment, and let it run through your fingers. Actually, I encourage everyone to do this. You will feel that this is a mix of sand and clay, and the clay will feel very sticky on your hand, and then these nice, rounded pebbles and cobbles of mainly quartz, OK? Most of which is present here is quartz. Student - Sand and all that is what is left over after the quartz was left. C. - Well, basically, you said it yourself. This is a very poorly sorted sand pile. This is a mix of different grain sizes, which indicates that it was dropped very rapidly. Now, what does the rounding tell you? Jill - it was well sorted. C. - ...well traveled. It is not well sorted, it is poorly sorted. Yeah, the rounding tells you that this quartz cobble started off somewhere far away and then it traveled a long distance to get here and as it traveled it got more and more rounded. This one must have started off a little bit closer. Alright, because this one is a little bit more angular. And that is typical of river systems because river systems end up draining a whole area. Rocks are dropping into them from far away and nearby and they are both tumbling downstream together. And, Jill, that is how you interpreted this, right? Jill - yeah, well no, sorry, I was off in a zone. C. - Jill, how would we interpret this deposit, how did this form? Jill - Well, basically, it came off of an uplift, and it traveled downward, and it was deposited into a system of water...C. - OK, what kind of water? Jill - Probably very fast. C. - OK, good, why do you say that? Jill - Because, it looks like they are rounded, I mean...obviously they passed through...Student - ...it is the size of the rock...C. Yeah, it is the size. Student - it is a well-rounded big rock. C. - Yeah, it is obviously a well-rounded, nice big cobble of quartz. And, it takes a lot of water energy to move something this size. Jill - Yeah, definitely. C. - OK, good, so what kind of body of water has the energy to move big cobbles like this? Jill - River, a river. C. - Yeah. Rivers, OK? Because we just saw, in fact, I just destroyed my vocal chords trying to shout over - rivers have a lot of energy. Whereas a lake does not have so much, a swamp - less. The ocean has a fair amount of energy, but you generally do not get big cobbles like this in an ocean because as soon as rivers flow into the ocean, they slow down, and then they drop all these things, and then they carry maybe the sand and the mud further out into the ocean. Those are all that really make it into the ocean. So, this is a river deposit. And, when you think about it you might think it is a little bit weird, because we were just down at the river and we just hiked uphill, and now at the top of the hill we see these river deposits? What is going on here, Cathy? Cathy - The river was once up here? C. The river was once up here, she says. These were not recent flood deposits. So, these are ancient, and the reason I know that is I can come up with a rough date for these deposits based on fossils that we find within this same gravelly unit. Now, this gravelly unit here, do you think it is a particularly good setting for preserving fossil remains? Callan hits the “unit” with large cobble, again and again. C. - Do you think that is good for a fossil? All right. Think about the river here. As these things are moving along, all these boulders are smacking into one another and grinding around. This is a lousy environment for preserving fossils. It is a miracle that we have any fossils at all from this unit. The fossils that we do have from this unit are very poor and they have been broken up a bit but we can still identify them and they are dinosaur bones. Alright, we found 3 or 4 different dinosaur bones from this one unit. There are some sauropod fossils, sauropods are the big, sort of lumbering, vegetarian dinosaurs with the long necks. We found some of their teeth and some of their leg bones. OK, there is a species called Astrodon johnstoni, it is the state fossil of Maryland. Basically, Astrodon means star-tooth. Think about your molars in the back, and you have these little points for grinding. There is a series of five radiating ridges for grinding up vegetation. So, Astrodon johnstoni. Also, we found some raptor fossils in here. At any rate, these dinosaur fossils date back to the Cretaceous. Cretaceous is a period of geologic time that ended at about 65 million years ago. It started at about 120 million years ago. The best estimate for an age on this unit is about 100 million years old. One hundred million years ago a river was flowing along this area, and that river was meandering. It was cutting in at a cut bank and it was depositing materials on a point bar. This is an old point bar deposit. OK, remember we saw piles of gravels that look a lot like this being deposited down at Quantico Creek today. So, this river was no longer cutting down, it was simply meandering back and forth on the landscape. Now, something must have happened between what we were just talking about at the base of the hill, and the deposition of these river gravels. We have this great big mountain range that had gotten built up, right? The size of the Himalayas - what happened to that? It was eroded down to essentially a flat level, and over that flat level, this river was meandering back and forth depositing gravel. OK? Then at some point after that what happened? Sea-level dropped and what did the river do in response? It started cutting down again and carving new valleys like the valley that we spent most of the day hiking through, OK? So we have evidence here of a higher sea-level at some point where these rivers were meandering along depositing gravels as they flowed eastward from the west out toward the young Atlantic Ocean. The Atlantic Ocean, by the way at this point, was 100 million years old. The Atlantic Ocean was born 200 million years ago and these gravels were deposited 100 million years ago, therefore, that is about 100 million years into the history of the Atlantic. One of the reasons that I’m able to say that these rivers were flowing from the west to the east, is we find signatures of rocks that we know only come from the west. Like we find pieces of granite that we find from the Blue Ridge Province. And these Blue Ridge granites have blue-quartz in them. Which is an indication that these are from the Blue Ridge Province. Yeah, there is some nice blue-quartz in this sample to right up there by my thumbnail. It has sort of a purplish sheen to it. You guys see that? The other thing that sometimes we find here is quartz cobbles that have a trace fossil right in them. That tells us that that came from the west, the river brought it this direction deposited it here, therefore that river was flowing from west to east. The same direction the rivers are flowing today. Now when the Appalachians were real, real young, it was the opposite. The rivers were starting here in the highlands above our heads and draining off to the west. Student - that is why you find Appalachian rocks way out in the west - west of us...C. - Yeah, there is some fairly compelling evidence in fact that the Petrified Forest of Arizona was buried underneath Appalachian sand and mud. In Arizona - so we are talking Mississippi sized rivers draining these young Appalachian Mountains, transporting the sediments to the west, and then basically they snuffed out a forest out there in Arizona. We can go and pick up a certain mineral from those sands, and that zircon has a chemical signature that is more analogous to the Appalachians than it is to any local source out there like in the Rockies. So, it indicates again at that time the mountains were here and the lowland was there. Who has got their handout handy, the one with the colored map on the back? Callan explains map....Kp designation which stands for Cretaceous. The sub p there indicates the Potomac and this is called the Potomac group. They are exposed up and down the length of the Potomac and you find them on tops of the highest hills. Same unit atop Tyson's Corner. You find it on top of Mt. St. Alban where the National Cathedral is. You find it on top of Mount Pleasant in D.C. - river gravels, river gravels, river gravels....Say that three times fast. So, this surface on top of which the river gravels are deposited is a period of missing time. The last geologic evidence we have in this area is the intrusion of granites. That happened around 460 million years ago, and then the next thing that is recorded in this area is the deposition of this gravel on top of it, which happened 100 million years ago. So, 360 million years of geologic time are missing in this area. We can say nothing about them from Prince William Forest Park. You have to read the geologic record to find out what is missing from those 360 million years. OK? Student - How come no one could think about water or erosion? C. To erode away a Himalayan sized mountain range takes a fair amount of time, and so it took a long time to grind down those mountains to that level. Plus, during the Cretaceous, the world was quite warm and sea-level was quite high. There was very little glacial ice, if any, and at that point then you have this combine effect of having ground down the mountains plus sea-level being high and that is when it deposited gravel all over this area. Wow, so this is like a little mud stone, right. Student - I get extra credit. C. - I would not call this a schist, it does not have nice physical minerals, but I would not mind calling it a mudstone. This is a little clast of mudstone and this is very typical of some mudrock layers that are typical out in the Valley and Ridge Province and that would be consistent with the story of basically transporting eastward. That is rose quartz there...OK, the first thing we are going to do when we get back to the visitors center is use the restroom, and then we are going to go and visit a fossil tree and that fossil tree is growing during the same period and it was probably growing along the banks of the river.

This was deposited by a river after the Appalachian Mountains were ground down. It is Cretaceous in age. It never experienced mountain building. If this had gotten caught up in that collision in would not be a loose pile of gravel, mud, and sand, it would be a rock. What would we call this if this had gotten cemented together into a rock? A conglomerate. Nature's version of cement with big chunks set in a little fine-grained matrix.

And, I do not really know what that means, I mean....

...on the trail today you are not leaving behind your skeleton, but you are leaving behind traces of yourself. Right? So, the thing that this Skolithos worm tube tells us is that it is a piece of the Antietam Formation. Antietam Formation is a big sandstone unit that is out on the western slopes of the Blue Ridge. And you can find them near Antietam National Battlefield, where the bloodiest battle of the Civil War was fought. You can also find this same rock along portions of Skyline Drive and there is an area where David and I have hiked near 66. There is a nice big exposure of it near Front Royal. So, basically it is telling us that the river transport direction was westerly - consistent with the blue-quartz. Sedimentary transport from west to east.

...Fossilized Bald Cypress Tree. It is really not in any danger of being degraded or anything like that, but it is in danger of having stuff grow on it. It is the mineral itself that will break down. All quartz. The quartz was derived from Cretaceous river gravels...And as it met this wood, it percolated through the wood, soaked into it, a chemical reaction took place, and it precipitated silica in place of the wood. This similar process has occurred in the Potomac Formation. In Washington DC, when they were digging out the foundation for the Ronald Reagan Building, they found more of these there. Also, at the base of the Mayflower Hotel, they found these fossil tree trunks down there. And, what do all these areas have in common? They basically have these cretaceous, Potomac Group river gravel deposits. So, you can imagine growing along the banks of this ancient river, Cypress Trees. How would you recognize a Cypress Tree if you saw one today? Yeah, Bald Cypress, and they have got these weird structures that rise up out of the waters. They call them knees - Cypress knees. They poke up above. I noticed in a place up here there are little tension gashes and they are filled in with silica, too. You see that - these little gray, blobs cutting across up there? So, it is like the tree itself is being deformed. It is fracturing and then the silica is depositing in those cracks. Yeah, so David is asking a question I do not have the answer to which is where is all this silica coming from in the groundwater? The groundwater has various things dissolved in it at various places at various sources, you know, that is about as specific as I can get. David - Silica does not dissolve easily in rainwater. C. - Right. David - It has to be warm to dissolve.

C. -...when things die, they just tend to rot. Fossilization is a very rare circumstance, when an organism gets preserved over time. Yeah, so wood tends to rot, so things eat it, beetles eat it. Well, one of the interesting things that is contrasted in this specimen as opposed to the one they found underneath the Reagan Building, or underneath the future site of the Reagan Building, is that one is jet black. This one is very, very light colored, it has got rusty. It basically suggests more oxidized conditions in terms of its preservation. Student - Where is the other one? C. - The other one is in Rock Creek Park. If you take my Bedrock of DC Geology Trip, then I will show it to you. It is jet black and it is also got pyrite preserved in it. Pyrite is again something that breaks down in the presence of oxygen as we have seen today at the Cabin Branch Pyrite mine...where it broke down into rust and sulfuric acid...so, it is more of a typical preservational environment. Low oxygen is more likely to be preserved. So, this is somewhat anomalous, but it is a beautiful specimen. What I just love about it is the grain of the wood here.

(Last segment - Granite outcrop in creek)

...water to get in there. What happens to water in the winter? It freezes. The water freezes and expands in volume by 9%. So, that opens up that crack a little bit wider. That means it is more than likely going to break down pieces, and when those pieces get broken out you carve out a little valley in the rock, right here. The quartz itself is stable, right? But, the neighboring area is not necessarily as stable. So, if you look around this area, you can actually see this quartz vein has actually become this little valley here and it narrows down...Do not take my word for it, come see. Now I want somebody who has never taken a class with me ever before, what is this? A sausage! What is the word for sausage? A boudinage! Oui! A boudinage! Alright, there is a beautiful boudinage in the last quartz vein, there. Now in order for boudinage to happen, it has got to be hot. It has got to be under lots of pressure, right? That is something that I said happened about 10-15km depth in the crust. So, that boudinage must have taken place during mountain building when this rock was still deep and hot, after the granite had already solidified because you ca not break a granite. It went through the quartz vein until the granite was already solid, right? So sometime after 460 million years ago, but before 100 million years ago. (Dave - Does the orientation of that, uh, boudinage tell you anything about the forces? C. - It well could. I have not measured its orientation myself, so I have not even thought about trying to put that into a regional context. But, yes, orientation of different rock structures like foliation or dikes, um - joints which are what we call these little cracks in the rock - those all often tell us something interesting about the forces that went to work on the rock. Now where Adrianna (student) is standing, we see a really interesting feature. Alright, here this granite dike has been faulted. You see here? This crack is not just a crack, it is a crack on which the two sides have moved relative to one another. There is an offset here about 1 inch in this granite dike. And, look here, there is another segment and it is offset about a centimeter. And, then another one, and another one, and another one, and another one. Do you guys see that? It has basically been broken and the rocks over there where Adrianna is standing have moved probably about, you know, just judging from this alone, maybe about by 5 inches that way relative to the rocks where I’m standing. That is a brittle behavior, OK? That is strictly breaking the rock. Alright, you do not see any real evidence of flow, there, OK, unlike the boudinage. (Background discussion/question...C - No, because this water does not have a lot of quartz in it. In order to get quartz to dissolve in water as Davis was pointing out earlier, it has generally got to be kind of warm to dissolve quartz better than cold water like this.) Student - What is the difference between a dike and a vein? C. A vein is just one mineral - like we saw epidote vein in the greenstone and we see quartz veins here. But, a dike is many minerals because it is an igneous rock. It is a tabular mass of igneous rock. And this is - this crack opened up, magma squirted into that crack, solidified into rock, and later it was broken and faulted. David - Wherever you see lines and stuff, you have faults. C. - We can only call it a fault if we have clear evidence of offset on either side. Still, like this one here maybe a fault as well, but I do not have anything good that tells me there is an offset on either side. Jill - So, instead of displacement in a rock, it is just a brittle behavior? C. - You might note that it is a brittle behavior that accommodates a displacement. The displacement can happen by flow or it can happen by breakage. In this case, it is breakage. Jill - It is a displacement? C. - Yeah, it is displaced. (...a 2 second bit of talking over each other/discussion back and forth between David and Callan.) C. - Cathy had a good question like did this happen during the collision? Alright, it is a great question. I would say that this is such a strictly brittle behavior (we can even see like little shards of the dike in there) right there along that zone, that I would say that this happened sometime after these rocks cooled down. And, earlier, I evoke this tremendous mass of rock overlying this location, right? 10-15 km of overlying rock that has been removed. Now, so does that mean that this rock, right here, has been exactly at this point three dimensionally in space through all of time and that there were mountains 15 kilometers tall on top us and have been beveled down to exactly this point? Or, did this rock start off 15 kilometers down and then basically uplift as erosion went to work on the landscape? Or, was it both? So, maybe it started off 7 kilometers down with 7 kilometer tall mountains. The mountains were eroded away, that means the crust is lighter and it pops up. Then more erosion goes to work on it. So, that means the crust is lighter and it pops up. More erosion goes to work - finally exposing the granite at the surface. David - are joints in granite often a loading and unloading feature anyway? C. - Well, a lot of joints in granite are unloading features. A joint is what you call a crack in the rock along which no movement has occurred. But, oftentimes we see that they are parallel to the topography. And these are distinctly not parallel to the topography. They are vertical. If we were to see a similar joint set running through the rock like this way, you know these rocks were under lots of pressure - now on the surface they are under no pressure. Sometimes we see granite actually expand, and then that thing fractures as it expands out, and those fractures then run like this, like an onion skin. That is stuff you see up in the high Sierras in California. Topher (sp?) was just saying he would been out there, up in Lake Tahoe - and then up in Yosemite to see these big granite domes, like Half-Dome, which are sheeting off layer after layer because the granite is actually unloading, and the sheets are just popping off. Are you making a movie of me? Jill - yeah. C. Just do not put it on You-tube or anything, OK? Alright, David noticed something cool, Let us turn our attention over this way.

Look at this. There are two intersecting joint sets here. Now, a joint set is basically more than one joint that is oriented the same way. So, we have got one joint that is basically going like this. OK, very regular. And, you have got another joint set that is going like this through the rock, also very regular. Their intersection produces these little columns like square columns of granite that go downwards, right. So, like we might actually see some up movement - no, none of them are loose. Well, anyhow, these things may be related to the unloading but if they were related to unloading, I would expect to see a third joint going like this through it basically divvying it up into tubes. We do not see that, but I expect it has something to do with tectonic readjustment during the uplift process. Alright, and after the rocks are cooling down and getting uplifted as the overlying rock gets stripped away by erosion, they crack, you know that is a stressful experience for a rock. It happens vertically, sometimes like 7 kilometers or 10 kilometers, something like that. Great observation. Now, what is colonizing those cracks there? Student -What? C. - Colonizing the cracks? Student - Lichen. C. Yes, and moss. Yeah, this is lichen. This is a crustose lichen, and this is a foliose lichen. Foliose lichen has leaves, right, like folios. And, the crustose is like crust on the surface of the rock. Um, yeah, because those cracks end up holding water, that is a good place for moss. Moss likes that - it grows along those cracks. You know, if I was to take a picture of just the moss here, to show you where the moss wants to cover up the joints...... (river is too loud).

How old is this granite? 464 million years old, + or - 5. That means somewhere in the range of 459-469 million years. OK, what else have you guys noticed? There are plenty of other cool things to talk about here? I'm going to climb back over there. C. - Good. I heard nickpoint, I heard waterfall, I heard pothole. OK, the river here is adjusting from a higher level towards a lower level. You can see that it is carving out a nice, deep valley downstream, whereas upstream we do not see that big of a valley. There is a valley, certainly, but its not a serious a size as it is downstream. There is a series of waterfalls downstream from here, and the river is adjusting to a ....level, over and over and over again. Somebody brought up the term nickpoint. I think you did. The profile of a river is like where it starts off at a higher elevation and then it is descending towards a lower elevation. Those little nickpoints are where the waterfalls are. Um, this is a nickpoint right here. This nickpoint is retreating in an upstream direction. Over time, the river will adjust, and basically will be cutting down in an upstream direction, and then the downstream area, if it gets too steep will try to get flat, by mass wasting which will widen the stream valley. Oftentimes we talk about the Grand Canyon haven been cut by the Colorado River. It is only partly true. The Grand Canyon was cut deeper by the Colorado River, and the Grand Canyon got wider over time due to a landslide, not wasting events. So, gravity does not like having a whole bunch of rock supported by neighboring rock. It is more likely to collapse. So, that is the same thing here. The Quantico creek cuts downward, and over time the valley has been widened and widened and widened. Sometime on your own come back to downtown Dumfries and see how wide the valley is, because it is quite wide. Alright, questions? Jill - Did you say earlier that was an example of columnar jointing? C. - No, I was just saying that the intersection of these two joints just end up making these kind of vertical four sided columns of granite. Like you take a block of cheese you go chop, chop, chop and chop, chop, chop. You end up having these little columns of cheese. It is not columnar jointing. It is a completely different process.

Where the moss was the first one to colonize this joint, so you can see that this joint is filled in with moss, and here there is frost wedging to get this expansion of the dike, and various other process have made a little deposit of dirt here in the crack. And, a seed landed in that dirt, and the seed took root. Is this an ideal place for a tree? Probably not. But, it is growing where it ended up. In time of really high floods, you know it is probably more than likely to be stripped away. Notice that the majority of the trunks coming off of this thing are all tilted in a downstream direction. OK, that probably happened during flooding. Um, yeah so, probably not ideal...

Jill - I have a question about nickpoints. Is it like the vertical cut in the waterfall? C. - A nickpoint is basically something we describe on a river profile. The way we recognize nickpoints is we look for water dropping from one level to another. Jill - it is not like an event...C. - it is a feature. Jill - ...it is a feature. C. - And, I would only be comfortable here saying this is one nickpoint here, and there is another waterfall downstream where you get another sort of 10 foot adjustment. I would say that is a second nickpoint. And, one of the neat things at Great Falls is that as you hike along the Billy Goat Trail is, when you go up to Great Falls you can clearly see one, two, three jumps in elevation. There are three nickpoints bunched together at Great Falls. Here, they are more spread out. Jill - but there was an event that created it, right? Callan - Basically, as sea-level drops a new water fall develops there and then that starts working its way upstream. So long as it outpaces sea-level rise it is going to keep propagating upstream. Dave - ...sea levels are rising. C. - Well yeah, I mean sea levels are rising, so lower nickpoints could get drowned and then there is not going to be any more erosion going on. Jill - so basically they are faults...they are faults? C. - No, a fault is a break in the rock in which movement has occurred. These are simply levels in the rock - the river has eroded down to this level, then as base level drops, OK, the river is now eroding down to this level. So, a waterfall develops here and then it moves upstream over time. But, the actual rock underneath is not necessarily faulting. Jill - OK.

Yeah, this is an interesting blob here. I'm noticing this shape. It juts inward here and it juts outward there. It appears to be faulted where this side has moved over to the right relative to that side. That side moved to the left. The way we typically describe these things is when you have a fault - say there is a fault running through here about like that, OK? You look across to the other side, and you use the direction that side tends to move. In this case, the other side looks like it went to the left. It's a left-lateral fault.

--- T R A N S C R I P T --- E N D S ---

As before, I would be pleased to hear any comments / insights / suggestions you might have.

Labels: field trips, nova, piedmont, teaching

Getting ready for a backpacking trip (to the Blue Ridge), and Lola wants in on the action. These photos aren't posed -- she seriously went over and inserted herself into the backpack belt loop!

This cat cracks me up!

Labels: field trips, lola

One of my most dedicated students (a) recorded our field trip last week to the Billy Goat Trail, and (b) transcribed it. Because I'm pretty much overworked at this point, I haven't been very blogophilic over the past couple of days. My apologies. So I'm going to offer you Jill's transcription of the Billy Goat Trail geology field trip instead. I've made a few small edits to clarify, but otherwise it's her transcription of our discussion/my lecturing at the various stops. I find it an interesting document... who would have ever thought anyone would pay this much attention to what I have to say?

--- T R A N S C R I P T --- B E G I N S ---

Billy Goat Trail Field Notes - April 8, 2008

Canal - C and O Canal stands for Chesapeake and Ohio. It's the canal that was originally intended to link the Chesapeake Bay watershed with the Ohio River. The Ohio River drains into the Mississippi River. So it's going to basically provide a watery link across the Appalachians. This specific structure right here as part of the canal, is what? It's a lock. The reason they went through all the trouble of building the canal where there's a river right there is you can't sail a river up a waterfall. Right here, there's a major waterfall [Great Falls] that prohibits navigation upstream and downstream. They built this canal where boats could sail upstream in a series of steps. These boats were actually pulled upstream. Technically, they weren't sailing. They were pulled along by mules. The mules were attached to the boat by a rope. The mules would pull the boat through these narrow, little chambers. Then these gates would swing shut at the downstream end and they would open up these gates at the upstream end. And, water would fill it up until the lock was filled with water at the upstream level, there. And then the boat would be pulled on out and do the same thing making steps uphill. Only when you do something like that, allowing a boat to float to a higher level, can you actually move a boat in the uphill direction. And they would do the same thing going downhill. Again, you can''t sail a boat down the waterfall very easily either. It's a little bit easier than sailing it up, but it's still not very safe. So, the C and O Canal was built for that purpose. It was originally the brainchild of none other than George Washington who originally tried to build the canal to get around Great Falls on the other side - on the Virginia side; called the Patowmack Canal. It's a very small canal. You can see its remains today. But, this (the C and O Canal) was a more successful canal - ultimately it was not completely successful. Ground was broken on it by John Quincy Adams about 5 miles downstream from here. He took that first shovel, and couldn't get that shovel into the ground. He tried again and again and he broke a sweat - it was very embarrassing and then he was a very staid individual and he rolled up his sleeves and played the part of like... "I'm going to get this!"...and so eventually that's when the canal construction began. The canal never made it to the Ohio River. It made it as far west as Cumberland, Maryland. In fact, the canal is now over 184.5 miles long. It's almost 185 miles long; it's quite long. At some point, the Baltimore/Ohio Railroad was started. The Baltimore/Ohio Railroad ultimately proved to be a more efficient means of extracting the natural wealth from the Appalachians; timber, and etc... And, the C and O Canal fell into disuse and eventually it was abandoned. At some point, developers were talking about taking this area and turning it into a highway that ran East/West along the Potomac River. Then there was this Supreme Court Justice who stepped in and said, "That's a lousy idea. It's a beautiful area. We should preserve it as a National Park." That Supreme Court Justice's name was William O. Douglas. He challenged a bunch of senators and editors of various Washington newspapers to join him on a walk. They went up to Cumberland, Maryland and they walked down the length of the canal to Georgetown where it ends. At the end, all of them were convinced that this was a place worth saving. And so, it became a National Park thanks to that one man saying, "we need to preserve this place." The reason we're able to come here today and actually look at rocks and experience the landscape is thanks to those efforts made by him and others inspired by him. So, that's why this area is still in a reasonably natural state.

The Billy Goat Trail starts about a quarter mile downstream. We're going to walk the Towpath where the mules once towed the barges up and down the canal. Until we get to the start of the trail.

It's a bridge. However, that's a really big abutment for a teeny bridge like that. The only thing going over that bridge is people. Yet they've got these massive abutments that are 40-50 feet thick. (You can see this one goes off into the woods that way: the abutment). Why would they go through the trouble of making a massive, racking structure just for the sake of a little footbridge? Because of flooding - yeah. This is not a structure for a bridge. This has to do with flooding. Explain yourself. If you're a canal engineer, and you spend years of your life and blood, sweat, and tears making that canal, you don't want the canal destroyed by a flood, right?...shutting down commerce from east to west. You want some kind of a fail/safe that you can activate in times of flooding. That's what this is. This is a flood control structure. You can see that there are grooves there, and in those grooves are slotted wooden structures, kind of like this one that I'm standing on. They're thin at the edge, thick in the middle, and that allows them to resist water slamming into them. And, think about that for a second. If you just walk, ...walk past this amazing view over there to the right, and you saw the Potomac River down 45 feet below you, -- during times of flooding the Potomac River level is up here - during times of flooding the discharge increases and the depth increases, so that the river is actually where you're up here standing, now, during times of highest flooding. And that could be totally destructive to your canal. So, this thing is put here so that in times of flooding they could act quickly and move these things in and make a big wall there. The flood waters slam into that wall and they could divert it off into the woods here and dump back into the Potomac River's main gorge. That main gorge is what we're going to be hiking along today and as we begin walking along the Billy Goat Trail, which I see is officially closed... as we begin walking on the Billy Goat Trail, keep your eyes peeled for evidence of flooding. You're going to see some evidence almost immediately after we start down the trail. Some of you are going to recognize that evidence. Some of you are going to walk right by it and not notice it. Our goal today is to turn up our observation meter so we are observing more. So anybody once you see some evidence that indicates flooding, call it to my attention and we'll stop and we'll discuss. (Question, John.) OK, there is sort of a wetland area right here - a little sag area where the water table is intersecting the surface - we're going to talk about groundwater in lecture next week. Basically, the groundwater is right on the surface so you get standing water there - a small little wetland. Good observation but that doesn't indicate flooding. (Jill - how about all those trees and brush just kind of pushed to the side?) Good, all right, it's a good observation - it's got something to do with trees...

OK. I'm expecting you guys to pay attention today. Probably you're going to want to take notes because ultimately what I'm expecting you to produce for me as a result of this field trip is a summary paper. This paper is going to be about 3 pages long - something like that and the paper is going to describe the geology of the Billy Goat Trail based on what we observe today. So this paper is going to be broken down, essentially, into an observation and then a geologist's interpretation of that observation. And then another observation and how a geologist interprets that. And so by talking about the physical evidence, and then separating it from the story that geologists tell based on that physical evidence, you're going to get an overall history of what happened to these rocks over time. (The paper is due in two weeks).

Head of the Trail - walking from the beginning of BGT.

Right, so during flood times, the water is coming from upriver, it's slamming into that flood diversion structure, and it ...over the landscape in this direction. So you'll see that the trees here are preferentially tilted in that direction. Do you see this one? How it's tilted in that way? This one, in fact, used to have this as its main trunk. That main trunk was killed and a little branch became the new trunk. Or look at this one over here. See how this one is pushed out in the same direction? Both of the original trunks broke off. Here was one, here was the second. Then branches became the new main trunk of that tree. Do you guys see that? -- tilted in a downstream direction. And, if you look around, you'll see plenty... now just tilted trees doesn't necessarily imply flooding. Trees that are all tilted in a common direction imply that they were all knocked down by a similar force. Knocked down but not killed. See how many tilted trees you can count.

Not creep - creep is on a slope. This was not creep. Tilting trees.

Knocked down by a flood, then it continued growing. Those do happen to be knocked down in the same direction but I'm not sure they were knocked down by a flood. Basically because those weren't knocked down last time I was here, and we haven't had a flood since then. I'm extrapolating that they were not knocked down by a flood. Furthermore, there's still dirt in the root. If you had a flood up here that was strong enough to knock down a tree it would likely have stripped away all that dirt.

We do have a couple of people coming through. We do want to clear - just step aside and make a path - part the Red Sea here.

John has made an observation that there's a round boulder up there. And that round boulder looks really different than most of these angular boulders that we see up here. John, is it also the same sort of stuff - does it look the same in terms of its composition? No, so maybe that could have come from somewhere else and the rounding suggests what, Elizabeth? It traveled a long distance (very good, Sal), OK. Remember the farther a sedimentary grain travels the more rounded it gets. So, flood waters may have deposited that, or maybe the Potomac River used to be flowing up here at this level. We'll talk more about that possibility later on when we see more of these boulders. It's a little premature to get into that, but it's - uh - a pretty big boulder. It's the sort of thing that wouldn't be picked up by the current and carried in a suspended load. It's more likely to be bed load along the bottom. So that indicates that that may be evidence that this used to be the bottom of the Potomac River before it incised to a deeper level.

What I'm stopping here for is where we're starting to see some more rocks. We're getting down closer to the river and because this area is more frequently subjected to flooding, that means there's less vegetation here. There's less dirt here. And, we can see more rock here. Your assignment over the next two minutes is to figure out what kind of rock this is. I'll give you two minutes - you're welcome to roam all around this area. What you want to do is you want to find nice, clean surfaces and try and identify the minerals, the texture, and ultimately the kind of rock that this is. Keep in mind that there is junk growing on the rock surface like this. What is this thing? It's a lichen, right. Lichen is a mix of algae and fungus that grows on rock surfaces. So, don't look at the lichens; they will deceive you. There are many different colors; these grey blobs are lichens, there are black ones, there are orange ones. You want to look for nice clean rock surfaces that don't have any lichens growing on them. OK, two minutes!

OK, what I would recommend everybody do is find yourself a nice, hunky seat. We're going to be here about 10-15 minutes, discussing. Somebody start us off with an observation about some of the different minerals that you've seen, or some of the textures that you've seen. Quartz. Big blobs of quartz here (she's got acid she's been dropping and the rocks aren't fizzing - not calcite). Some of those are very striking and obvious - very creamy looking - big blobs like right here, right here on that knob, etc. Good. What other minerals do we see here? Mica - muscovite micas, the silvery micas. Sometimes it's really obvious like, look at this, look at the shine on that, great. Nice and shiny mica. What can you tell me about all those flakes of mica? Are they oriented in random directions? Or are they all aligned in a common direction (Jill - they're in sheets). They're in sheets, says Jill. Would you agree with that John? How about you Elizabeth? OK? Yes, all the micas are aligned in sheets. And, obviously some of these are boulders broken off. Some are bedrock where the sheets are still in their original position. Like the one Jorge is sitting on - this one here - the one Elizabeth is sitting on. What is the orientation of those sheets in space? If you took your hand and made your hand a flake of mica how would you orient it in space? OK, good. Doug is showing us with his hand the orientation of all those flakes of mica in space. So what is that? When you get these layers of quartz and mica all basically strung out in these vertically oriented sheets? It's metamorphic foliation. When we studied metamorphic rocks, there are foliated metamorphic rocks and non-foliated metamorphic rocks. These are foliated. What does it take to produce foliated metamorphic rocks? Pressure, very good, Vivian. What kind of pressure? (Confining pressure is what happens to you when you're at the bottom of a new swimming pool: it may cause your ears to pop, but it doesn't realign your head in a new direction). The answer is differential pressure. So, what's happening here is that these rocks have been compressed, OK? Force is pushing on them this way, and then another force is pushing on them this way. So, all those original minerals got squished together, and they ended up lining up straight up and down as they were squeezed from the sides. So, this is a metamorphic rock. You guys have just figured out something really important about these rocks. What tectonic event creates regional metamorphic rocks that have foliation? Orogeny. So, these rocks have experienced orogeny. They've been squished from the sides due to that tectonic collision. Whoa! That's a pretty big insight to come to about these rocks. I'm sure this raises all kinds of questions in your head. Go ahead and ask some of those questions.

(Vivian - no, talus is often great big blocks like this - talus usually accumulates at the base of a cliff. You might be able to call some of this talus - like this could be a block of talus. This is not - this is bedrock. It's still attached to the solid earth. It's not that it's broken off and made into a piece of sediment like this. You'll see some areas today where you'll see some large accumulations of boulder piles, and I guess you could call that talus. Remember talus is specifically when it's falling into place.)

Jill - we're in the Coastal Plain? No, we're in the Piedmont. Is this a part of the Taconian Orogeny? Well, one way we can answer that question - Jill's bringing up the Taconian Orogeny. I want you guys to think back to when we talked about the geologic history of Virginia in lecture. We talked about this mountain building event that happened in the early Paleozoic/late Ordovician Period, we call it the Taconian Orogeny because it built up the Taconic Mountains in New York - um - what caused that Taconian Orogeny? (Jill - we've discussed this two days ago - maybe I'll put you on hold there, maybe somebody else can remember what caused the Taconian Orogeny?) A volcanic chain of islands bumping into us? Exactly.

Awhile ago, there was an ocean off the East coast of the United States. If you were able to go back in time 500 million years, and hover over North America, you would have seen something that looked roughly like this. Here you've got a smaller North American continent and it's missing some pieces. Notice that Florida's not there, California's not there, Alaska's not there. OK, those have all been added on more recently. 500 million years ago California, Florida, and Alaska were not yet part of North America. And, our location is marked right here. Now actually at that time what we'd really see is this (see map rotated) - North America was in a different position at that time. And, since 500 million years ago North America has rotated and moved north. OK, but at that time it was on the equator and it was rotated in a different position. So today what we call the East coast was really the southwest coast. Let's just call it the East coast and keep it simple. Does that work for you guys? OK. Notice what's offshore there. There's a subduction zone marked on the oceanic crust by a deep trench, and then next to that, paralleling the trench, is a chain of volcanic islands; a volcanic island arc. Subduction is bringing that volcanic island arc closer and closer to North America. It collides with North America. Jill is fortunate because she took my Prince William Forest trip on Sunday. We actually got to go and visit some of the rocks from those islands. They're preserved down by Quantico, Virginia. In between those islands and North America, a bunch of sediments got squished out. I want to remind you guys about the concept of an accretionary wedge. Accretionary wedge. What is an accretionary wedge? Right. Sediments that get scraped off the ocean floor at the sight of a subduction zone. OK, so remember in class I offered you the analogy of my arm covered in peanut butter, and my other arm scraping that peanut butter that went there? There's another analogy at the bottom of a bulldozer. So there's this big pile of oceanic sediments building up at this trench at the sight of subduction. And, those sediments then begin to squash between the volcanic islands and North America. I gave you guys the awful kitten analogy, right? So, this is the crushed-up kitten. These are these poor little oceanic sediments that are getting squashed between a Mac truck, North America, and a mini-Cooper, these volcanic islands. So, the kitten's little bones started off in many different orientations when they rotate to newer orientation which defines the foliation of the kitten. So, that's what you're looking at here, guys. You're looking at rocks that used to be sediments on the floor of an ancient ocean, and got crushed up and metamorphosed into the rocks that you're standing on now. So, if they're now metamorphic rocks and they used to be sedimentary rocks, what kind of sedimentary rocks were they? (Basalt? No, basalt is not a sedimentary rock - basalt is an igneous rock.) Did anyone see any grains when they were looking at these rocks - any grain size? Grains? Check this out, OK? What does this look like? You can see sand grains in there. There are sand grains in here, and sand grains are made out of what mineral? Quartz. Good. What is reacting to make the mica? What is reacting under elevated conditions of heat and pressure to make mica? It used to be greywacke. Greywacke is a mixture of sand and mud. Yeah, mud is made out of clay minerals. These clay minerals are not stable at high temperatures and pressures. So when they experience it, they turn into mica. Muscovite mica that's all lined up in the same direction. So these rocks used to be layers of sand and mud at the bottom of this ancient ocean basin (so-it's metagreyacke - Laura). Right, good. So, for the rest of the day, I'm going to call them metagreywacke And, I'm going to use that term over a more traditional metamorphic rock name like schist because I feel like it tells us more. All that "schist" tells you is it's a metamorphic rock. The term metagreywacke tells us a metamorphic rock and it used to be greywacke. So, it's got a double meaning there. Now, what can you guys tell me about how greywacke accumulates or where it accumulates? (Jill - an accretionary wedge. C. - An accretionary wedge just takes whatever is there and jumbles it into a big pile). Greywacke accumulates from submarine fans at the bottom of the sea. What is bringing sediment down to that deep location? What depositional force? Turbidity flow. You guys remember turbidity currents? Turbidity currents are these big, sediment rich flows that flow down across the bottom of the sea floor. When they slow down, what gets dropped first? Big grains. What gets dropped next? The finer grain stuff. And you end up with this overall sedimentary structure known as graded bedding. Anybody notice any graded bedding here today? (Here's an example...)

OK, so there may have been some preserved but then the river eroded out those boulders and transported them away, that's one reason. But we saw lots of rock left. OK - maybe there wasn't that much there to begin with? That's a possibility. They changed too much - they've been metamorphosed? Yeah! Metamorphosis tends to destroy those original sedimentary features, right. I mean, even though the mud isn't mud anymore, it's now mica. Yeah, metamorphosis has destroyed most of the graded bedding. If you go up and down the Piedmont, back and forth across the Piedmont, it's very, very rare to find graded bedding still preserved in the metagreywacke of the Piedmont. The only place that I'm aware of that you can still see it - no I take that back - there are two places that I know of where you can still find it. One place is here, and the other place is out near Sugarloaf Mountain. But everywhere else it's been destroyed. Like, Jill, did we see any at Prince William Forest Park? (Jill - uh, no). No, right, it was basically too intensely metamorphosed and the graded bedding is gone.

OK, let's try and bring this around full circle now at this point. If these sediments were originally accumulating as graded beds of greywacke, mixed of sand and mud, in an ocean basin, what ocean was that? The Iapetus Ocean - what the heck is that? Before the Atlantic. How does it relate to its name? The father of Atlas... The Atlantic Ocean is named for Atlas - the guy who held the world on his back. The ocean that came in the same place as the Atlantic but earlier is named for the Titan who fathered Atlas, and that was Atlas's dad, and that was Iapetus. So we call this ancient ocean basin the Iapetus Ocean. The Iapetus Ocean no longer exists. It's dead. The Iapetus Ocean was killed in a series of tectonic collisions. First, was a collision between these aforementioned volcanic islands and North America. Second, there was a microcontinent out there in the Iapetus Ocean - that crashed into North America. That microcontinent is now preserved as most of New England. Right, you can go up there and visit that ancient microcontinent. And then, finally, a much bigger land mass crashed into North America, finally killing off the Iapetus Ocean. What land mass is that? Yeah, Africa. Are you feeding them answers over there, John? OK, Africa crashed into North America, and that made a certain supercontinent that I'm certain that everybody knows, without John giving them a hint, -- Pangea. The moment when the Iapetus Ocean died was the moment Pangea was born. As soon as those continents butted up against one another, the Iapetus Ocean was gone.

We're talking about a geologic history here... we're talking about a collision. Exactly, very good, you've got the journalistic instinct. Who, what, when, where, why, when...so when did this happen? How can we answer that question? (By isotopic dating...) C - of what? What isotopic minerals would you choose to date here? The muscovite. That's right. The muscovite is a metamorphic mineral formed during the orogeny. So if you get an isotopic date on that it tells you when the orogeny happened. Well it turns out people have done exactly that. They've taken this muscovite mica and they've analyzed it, looking at the isotopes potassium 40 and argon 40 in that mica. And that gives you a date of 460 million years ago. That's the date of the Taconian Orogeny, Jill.

OK, so the Taconian Orogeny just to sum up here. The Taconian Orogeny was an episode of mountain building that occurred 460 million years ago. (Radioactive parent isotope is potassium 40 and argon 40 is the stable daughter product - question...)

We already noted back there that the rocks had been metamorphosed. Remember that metamorphism is one of the characteristic signatures of mountain building. You can identify a mountain belt even when the mountains themselves have eroded away by the presence of metamorphic rocks.

There were two other characteristics of mountain belts that we discussed in class. Vivian - what's one of them? Folding. And that's exactly what Doug noticed over here. He noticed that the metamorphic foliation has been folded up here. You guys see those sweeping folds going through these quartz layers here? Right here, you can see another one here. Down up, up and down again. Along the trail today, you will see dozens upon dozens examples of layers of folding. Sometimes it's a little hard to spot with the lichens growing all over them. You can see some here - you can see the layers go up and down and then up again. There's plenty - you guys are going to see some real nice, sexy examples of folding as we go along the trail. This isn't the most amazing spot, but since Doug noticed it, I wanted to point it out.

While we're on the topic, what's the third characteristic of mountain belts? Metamorphic rocks, deformed rocks (including folded or faulted rocks), and then the third characteristic is...? Come on guys, you can't take this for granted! Granite! Right. Granite. Remember granites are produced by partial melting when rocks get really hot. So, you want to keep your eyes peeled for granites along the trail today, as well. OK. What we're going to do...

Find yourself a spot where you've got a good, unobstructed view across the river to the other side. Remember, we're in Maryland, and we're looking across the river at Virginia. So, Virginia' on the other side. There's a feature I want to call your attention to here. Can everyone see there's a series of vertical gashes? Four of these gashes all in a row? All oriented in the same direction? If you look for the tallest tree over there, and then go down to the base of that tallest tree you'll see these deep gashes in the cliff face. Those are a series of igneous dikes. Dikes are what happens when a rock cracks open, magma squirts into a crack, then the magma solidifies into an igneous rock. Tell me something about the igneous rock that is inside these dikes. Is it more stable or less stable than the metagreywacke? Less stable. How do you know that Michael? More mafic - how do you know that from here? The color? You can see it looks a little bit darker. It's a mafic igneous rock? Ding! You're right. I'll give you a closer look at it here in a few minutes. But you can also see that these igneous dikes don't project out from the face of the cliff, they're sunk into the face of the cliff. Which means, that that rock 'rots' away more easily - more easily weathered. It's more easily broken down. Remember the Snickers bar that I made you suck on? Whatever is making up those dikes is more like the chocolate and less like the peanuts. It's easily etched away. Everybody with me on this? So, that supports the idea of it being mafic because mafic igneous rock has lots of iron and magnesium. Iron and magnesium like to oxidize. Now tell me this. How old are those dikes? Younger than 460 million years old. How do you know that? They're cutting through the metagreywacke. And, you can't have the dikes cut across the metagreywacke unless the metagreywacke already exists. Therefore the dikes must be younger than 460 million years old. Well it turns out their igneous dikes, so what can you do to them? You can date them isotopically. They've done isotopic dating on biotite that's present in those dikes, and biotite gives a crystallization age of 360 million years ago. Only 100 million years after the greywacke got metamorphosed to metagreywacke. Again, that number is 360 million years. Those dikes are 360 million years old - 100 years younger than the metagreywacke they cut across.

I want to point out that the second Appalachian mountain building event occurred 360 million years ago. This is the collision of that microcontinent with North America. So, as we said earlier, North American experienced a collision first with a mini-Cooper sized land mass of volcanic islands. Now, it's colliding with a good-sized sedan - the microcontinent. Eventually, it's going to collide with a Greyhound bus which, would be Africa. North America gets to collide with larger and larger land masses through time. This series of dikes over here occurred at the same time at that second episode of mountain building, sometimes called the Acadian Orogeny. You can see it well up in Acadia National Park, in Maine. (The highest point on the East Coast, still, is Klingman's Dome in Great Smoky Mountain National Park; 2nd highest is Mount Washington up in New Hampshire) (John - Avalonia up North and Carolinia in the Smoky Mountains?) (C.- That could well be true but...) We tend to divvy up these parts of the Piedmont and call them different terranes - I know there's a terrane called Carolina/Carolinina... but, I don't know if that's necessarily a microcontinent. I would only call it a microcontinent if it's made distinctly out of continental crust before it hit. Avalonia is the name of the microcontinent.

Doug did a great job earlier with his hand showing me the orientation of the foliation of these rocks. Again, we can all see the orientation down at our feet right now. It's oriented something like this. Now what I want you to do with your hands is show me the orientation of these dikes. I specifically chose this spot to view the dikes because we are looking directly down the barrel of these dikes. We're looking down that crack in the earth - it's coming straight towards us here. If we're looking down at our feet, we should expect to see the dikes right here. Where are they? What gives? There's a shift. It turns out the dikes are on our side, they're about 30 feet downstream. Let's go see them.

All right, look at this. Here's some almost vertical gashes in the rock. They have that same orientation. But, if you look (and this is actually a great time to be running this field trip because there's not leaves on the trees yet) if you look over there on the opposite side you can watch these go down and you would expect them to run into the middle of that cliff over there. But, that's not where you see the dikes on that side. Instead they're offset in an upstream direction on the Virginia side by about 30 feet. You guys see that? Pretty cool! What gives? Maybe, a fault? Let's discuss the evidence for faulting here. Oh, by the way. Here's an example right here - this boulder that my foot is on here. That is the igneous rock that makes up the dike. It's a kind of basalt - you remember basalt from lab, right - mafic and fine grained? And, what you see here, and I want everyone to come take a look at this after I move away, is that this basalt has visible flakes of biotite mica in it. Not muscovite mica, that silvery mica that we saw at the first stop, but instead biotite mica, which is jet black. You'll see these little shiny flakes of black biotite mica here in this special basalt. This basalt has a special name. It’s called a lamprophyre, because of those flakes of biotite mica in it, but, it's just a fancy name for a particular kind of basalt. Alright, again that name is lamprophyre. You'll see that in your handout that I gave you earlier. So, these are lamprophyre dikes. How old are the lamprophyre dikes again? 360 million years ago, which is the same age as the Acadian Orogeny. (That's coming from you John- one thing at a time, one thing at a time...) So, Laura please share with everybody your hypothesis on why the dikes do not line up from Virginia to Maryland. All right. Because there was a fault, and that fault offset the dikes on opposite sides of the Potomac River. Here's two diagrams. If you can't see these, move closer. Basically, here I have two different explanations for the offset of the dikes on either side of the Potomac River. The first explanation is that the dikes were originally straight and they were broken by a fault. What kind of fault would this be? Left-lateral or right-lateral? Right? Yes. Right because if you're looking across it looks like the other side has shifted to the right. Very good. The other explanation is that in fact, the dikes were not straight dikes. There's no rule that says if you crack open metagreywacke it must be a straight crack. The crack may have been jagged. Maybe that explains the offset well. Unfortunately the critical area we need to examine to answer this question is underneath the Potomac River. So, if we're going to answer this question, we're going to need to look around for additional lines of evidence. One piece of evidence has to do with the shape of the river. This is an aerial photograph of the Potomac River. We started off our hike today up here at the Great Falls Visitor Center. This white line going across the Potomac River is a dam where they divert water for D.C. Great Falls itself is this great, white blob here. And, then, we are right about here following the Billy Goat Trail along a very, very, very straight section of the Potomac River called Mather Gorge. Mather Gorge is what we're going to be hiking along for the rest of the trip today. Mather Gorge is named for Steven P. Mather, the original superintendent of the National Park Service. You'll find that the National Park Service has honored this guy endlessly. I think I've slept in four Steven P. Mather Memorial Campgrounds in National Parks around the country. They really love this guy. Anyway, Mather Gorge is named for him. Now, look at how straight Mather Gorge is. It is incredibly straight: It's as straight as an arrow. It's as straight as you would expect if there was a fault underneath the river there that had ground up the rock. Remember faults tend to break up rock into fault breccia. And that would be really easy for a river eroding into the landscape to erode away fault breccia opposed to solid bedrock. So, the actual shape of the river is suggestive of the fact that there may be a fault underlying the river at that location. Unfortunately, the only thing that we can use as a marker is these dikes. So, we don't have any other evidence of offset here because basically everything else is just smooshed up metagreyewacke. And, the place is the end of Mather Gorge which is here and here, where you might expect to see the fault exposed up out of the river, you can't really see any good evidence of it. Some geologists claim they've seen it up on the Rocky Islands that we walked by just before the fault diversion structure. I've been there and I've looked at the same outcrop and I don't see indisputable evidence of faulting there. I see a crack, but a crack doesn't mean a fault. ("Can you put divers in the river?" Sure you could put divers there at great expense and risk to the diver. Problem is at the bottom of the river there's all kinds of boulders covering up the bottom. And, there's silt and mud and big catfish and you're not really going to be able to get a good look at what's going on. The one thing you could do is you could back up the Potomac River for a couple of days, excavate away, and arrive at an answer to this question, but its not really that critical a question to arrive at an answer at.) Let me share another piece of evidence for you. Remember there's another way of explaining the offset in the dikes. It may be a fault but it could also be that the dikes were not originally straight. Here are two pictures of outcrops of the dikes. One is on the Virginia side and the other is on the Maryland side. Let's discuss the Maryland side, first. This is a photograph taken from Virginia looking at Maryland. You can see coming up from the river, one, two, three dikes. And up here, one, two, three, four dikes. One, two three. One, two, three, four. Three does not equal four. What's going on? Well, it looks like this middle one is actually branching. It splits into two arms there. When the rock cracks it was a jagged crack and the crack had two little fractures – two little arms that went on and those filled with magma. The other photo is over on the Virginia side. Again you see the lamprophyre dike here the metagreywacke host rock here. And you can see another one of those branching arms coming off the dike. The dikes are not in fact straight. Does that mean that there is no fault? No. A fault could break crooked dikes just as well as a fault could break a straight dike. So, do we have an answer to the question? No. We do not know which of these two hypotheses is correct. We have not been able to prove either one of them false, therefore, they both stand as possible explanations for the offset of these lamprophyre dikes. What questions do you have? Jill - what questions should we have? How about: "Sir, can we look at the lamprophyre, please?" Jill - can, I? OK, yes you may! Come here, stick your head in that hole and check out the lamprophyre up close, and see how it looks different than the metagreywacke. It's dark, fine-grained igneous rock and it has little flakes of biotite in it. It's going to be difficult to see from far away, you actually have to get about a foot away to see that. C I'm not lying to you, you can trust me. So, don't take my word for anything. Trust your own eyes and your own mind.

OK, why have I brought you over to look at this rock? It's fancy. Take it further. Jill - it's been fractured. There's some fracture. What do you see, Vivian? There's a lot of different joints in these rocks - remember joints are fractures along which no movement has occurred. Those are visible all over here making this very blocky landscape. Look at the other side. You can really see the joints. Good observation. But it's not why I brought you here. There's a nice big blob of quartz there. What kind of quartz is that? There's a lot of different kinds of quartz that we saw in our minerals lab. Smoky, rose, citrine, milky quartz - milky quartz, good. Milky quartz is generally whitish. Why is it whitish? Yes, it's got little tiny bubbles of water in it. That indicates how that quartz got there. It got there by hydrothermal fluids. OK, basically hot water in the earth had quartz dissolved in it and it precipitated out these big blobs of quartz. Very cool, this probably happened during the Taconian Orogeny, as well, when these rocks where nice and hot. Again, not why I brought you here. There's a beautiful fold here in graded bedding. Alright, do you see that really coarse-grained layer there that's been folded up? That used to be horizontal on the floor of the Iapetus Ocean deposited by a turbidity current and then during mountain building it got squished up and folded. Squished up and folded and it looks like the hydrothermal quartz was then placed as well. You can see another bed here below it pulling the same trick. Pretty cool, huh? Symptoms of mountain building.

Jill asks questions about source of sediments. Thank-you for being persistent with that.

John, pass me some clam shells. Did you guys notice all these clam shells all over the place all over here in these big sand piles? All right? What's up with that? So you're saying that these clams are the same age as the rocks? Turns out that these rocks have no fossils, whatsoever. For several reasons. One is, deposits in the deep ocean, there's not a whole lot alive down there. Second, these rocks may be older than multi-cellular life. So, they may not have any fossils in them for that reason. Third, they were metamorphosed so any fossils present would have been destroyed like most of the graded bedding. So, these are actually Recent clams. It's actually an Asian species of clam that's an invasive species colonizing North American waterways. It's a freshwater clam. So, these clams have come downstream from higher in the Potomac which means that they were deposited during floods. Just like the tilted over trees are evidence of flooding, so too are all these clam shells and sand deposits way up here above the level of the river. Unlike that big round boulder we saw earlier, this is the stuff that usually gets picked up by flood waters. This is like a little parachute very easily picked up by the waters and wafted around. Good. Let's go.

When does the Billy Goat Trail actually going to get tough? It's about to get Billy-Goaty. So what we're going to do is walk across an area called pothole alley. And as you walk across pothole alley you'll see why it got its name. And there's going to be lots of potholes there, you've got to be really careful. You want to use your hands and your feet. It's a good time to be putting away anything you've got in your hands and you've got your hands free to navigate the landscape. Jill - are you going to stop and talk a lot? C. - No I'm not going to talk at all. We're going to walk across it and then we're going to get to the other side and sit down on a nice broad plateau and have lunch overlooking Mather Gorge. OK?

(right after lunch) Maybe sand, maybe silt. Um, one of the things that you learn about these potholes is that if you take your hand and you reach inside and you run your finger around the inside you'll feel differences - that there are little ridges in there. There are different layers of quartz and mica. Quartz stays up in high relief because quartz is very resistant to erosion: it's hard. Mica on the other hand is soft and chemically unstable - it breaks down into clay at Earth's surface temperatures. So, what this is telling us is that something is preferentially etching away at the mica and leaving the quartz behind. Something really small has to get in there to do that job. Something like a grain of sand or like a grain of silt. So, pebbles may be part of the process, but, definitely sand or silt are part of the process. They're etching away at the mica and then maybe a pebble comes along and slams into these unsupported ridges of quartz and snaps them off. That would be one hypothesis, but the original etching is done by sand and silt. Based on these little ridges.

There's something else you may have noticed, and that is if you look across at the Virginia side, there's this very flat surface, basically parallel with the surface that we're on. Do you see that? Because if you look back up river, there's this sort of flat plateau, maybe not really flat, - it's etched into with all these potholes and stuff, but it basically continues across the Virginia side. That is one of those bedrock terraces ("straths"). They're older levels of the river that used to be the river bottom and then the river cut into a newer, deeper level. Some of the evidence that we have for this being the bottom of the river are these giant potholes. This sort of thing is not going to be scoured out in a flood. It's something where you've got the river working on it for centuries - maybe millennia. ...potholes... also, there are these great big boulders that we find up here. Boulders that were probably once bedload at the bottom of the Potomac River tumbling along, rolling downstream and then eventually when the Potomac cut into a deeper level, they were left high and dry up here on the surface. The next thing that we're going to stop and look at along the trail is one of those boulders that tells us about where the river was flowing from. On the other side (of the river) you see a hill. There is a hill on the other side that rises above this bedrock of terrace steps. That hill is called Glade Hill. On the top of Glade Hill you also find rounded boulders that have been transported downstream by the Potomac River. So the top of Glade Hill used to be the bottom of the Potomac River. So, the bottom of the Potomac River was above our heads and where we're standing now was still solid rock. Then the Potomac cut down to a deeper level. It carved out this bedrock terrace, made these potholes, deposited the boulders here, then it dropped again and cut down to a deeper level. The Potomac is incising over time. (This is not an entrenched meander because the Potomace does not meander here. There are areas where the Potomac does meander, like at the Paw Paw Bands. But, here of course the river is quite straight.)

OK, I want everyone to come and take a look at something. Wow. Alright. What I want you guys to do is I want you to stick your head in the cave. Tell me what you see! Stick your head in there and look at the ceiling. What are you seeing? Folds! You're seeing folds and what's being folded? Alternating layers of quartz and mica. The quartz is light colored milky quartz the mica is dark-colored biotite mixed in with muscovite. And as you look up there you can see that they're strung out in parallel layers. Light minerals - dark minerals. Light minerals, dark minerals, light minerals, dark minerals. It's a very coarse texture. We learned a name for that metamorphic texture - you got coarse alternating bands of light and dark minerals –gneiss. Gneissic banding. So, you got this foliation and remember that the foliating is formed due to differential pressure during mountain building. But what happens to the foliation, here, Laura? The foliation was folded. So you see that these alternating layers of quartz and mica that have been all folded up. And, that's an interesting thing because when you think about it, those layers themselves formed due to pressure in one direction. In order to get them to fold, you have to apply pressure from another direction. This is important stuff here. This tells us that these rocks have experienced more than one generation of deformation. They've been squeezed once. They got to sit still awhile, and they got squeezed again. OK? Questions on this outcrop?

OK., we're going to go down the path. We're not going to go far because we're going to see a stange, green boulder in the middle of the trail.

A Martian! This is an interesting rock, this is a greenstone, clever name. And, a greenstone is metamorphosed basalt. Where does basalt come from? Mafic lava. It's what basically happens when a volcano erupts mafic magma we call that basalt. If you want to see basalt forming today go to the Big Island of Hawaii or Iceland. If that basalt gets caught up in an orogeny, it gets metamorphosed and it becomes a greenstone. Basically, two metamorphic minerals grow - both of them colored green. And you met both of these metamorphic green minerals during our metamorphic rocks lab. Olivine is not metamorphic-that's igneous. I introduced you guys to 5 metamorphic minerals in that lab - garnet, kyanite, staurolite, and then these two. Chlorite - deep forest green, and pistachio colored green - epidote. Epidote indicates hot water in metamorphism. So what happened is this basalt flow got metamorphosed and it produced this greenstone. Now that brings us to the question of what are these little white blobs that are popping through here in different places? They are little round or ellipsoidal blobs of quartz.

Think of what this lava would be doing when it was first erupting. "Kitty eyes." Ignore her! Aren't they crystallizing. Sure, they're crystallizing and they're fine grained texture which makes them a basalt. What does a basalt do when it gets up to the surface and suddenly it's depressurized? Air bubbles... Remember lava often degasses at the surface causing little bubbles that we call vesicles and then those vesicles, those little swiss cheese like holes in the rock they can later get filled in with mineral deposits. In this case, quartz rich ground water flowing through this deposited quartz filling in these vesicles preserving the vesicles as... amydgules. Amydgules are these preserved gas bubbles. Now, I'm going into a lot of detail about this one boulder, even though this boulder is not from this area. This is like I mentioned, a visitor. It is one of these boulders that was deposited on the bottom of the Potomac River, before the Potomac River cut down to a deeper level. This is a piece of a very distinctive greenstone that is present out in the Blue Ridge Province. It's called the Catoctin Formation. I mentioned the Catoctin Formation when we talked about our Geologic history of Virginia, when I said that when Rodinia broke apart there were these big lava flows all over the landscape - flood basalts; that's the Catoctin Formation. Later on of course those flood basalts got metamorphosed during Appalachian Mountain building which made it green. Jill - so these are actually far deeper - have been layered deeper into the landscape, right? C. And the mountain building they got shoved up and erosion exposed them to the surface. The reason I go into all this detail about the identity of this boulder is I know where this boulder came from. I know that outcrops of amygular greenstone - the Blue Ridge province is west of here. So that indicates that when the Potomac River was flowing at this level, it was carrying sediments from the west to the east. Now that may seem obvious to you because of the Potomac today - it flows from west to east. But, we can say with some certainty based on the presence of this boulder right here that that boulder was doing the same thing in the past (Principle of Uniformity). It's a confirmation that the flow direction of the Potomac has been relatively constant at least since it was at this level. OK, I'm going to show you some other evidence if that. I'm going to point out some other boulders along the trail as we go along and they’re all going to have Blue Ridge identities. But, first I've got something even more spectacular to show you.

So I stopped here to show you this outcrop which might not look something too spectacular in the beginning, but once you understand what this thing is your eyes are going to pop out of your head and your jaw's going to drop. Get in close, take a look at this. What do we have here? "Rocks." (Eyes rolling) Sure... there's some nice folding. There's some potassium feldspar in there. See these peachy little potassium feldspars, here? They're opaque relative to the grey quartz here, no longer milky quartz, but grayish. Potassium feldspar, grey quartz - what is that? What are we looking at here? What are these little blobs of a mixture of coarse grained quartz and potassium feldspar? Granite! What's the third characteristic of mountain belts? Granite! You're looking at metagreywacke that's gotten heated up so much that part of the metagreywacke has melted. Not all of it, but some of it. Remember the idea of partial melting where you start off with a rock with a bunch of different minerals. Then if you heat it up, some of those minerals basically dissolve into liquid magma and some of them stay as a solid residue. So, ones that are more likely to melt are the felsic ones. Those that are less likely to melt are the mafic ones. So, essentially what you're seeing here is granite magma being sweated out from super-hot metagreywacke. This rock was originally deposited as sediment at the bottom of the Iapetus Ocean. Then it became metamorphosed and now part of it is becoming igneous. It's all three parts of the rock cycle right here in one outcrop. Jill - it's coming back to itself. C. - right, its coming back to itself. Right now its being weathered off and producing new sediments, so the cycle runs full circle, right? This is a granite being born. You've just got these little blobs of granite magma leaking out of this rock. You've got the midwife's perspective here watching this granite in the act of being born. This granite magma is liquid it's going to go upward in the crust like the blobs in a lava lamp and eventually it will join with other blobs and its going to cool together into a big granite pluton somewhere else. But, here it never made it that far. It just started to sweat out of the rock and then it stopped. So we are lucky enough here to have this snapshot moment of the rock cycle caught in the act: caught red-handed where metasedimentary rock is actually converted into igneous rock. It would have had to be really hot for this to happen. Probably around 400 degrees or 450 degrees; something like that. But because it's coarse grained it cooled slowly underground. Now it's up at the surface today, but originally it cooled down slowly deep underground. We some evidence in this area where we see boudinage. Little sausage shapes squeezed out. Remember we see that at about 10-15 kilometers depth. So this is a rock that formed about 15 kilometers beneath the surface when it was about 450 degrees. Now are there 15 kilometers or rock above us now? No, they've been removed. What removed them? Erosion, yeah. Erosion ground down these ancestral mountains and exposed their roots. The rocks that we're looking at here were once at the roots of the Appalachian Mountains. (Laura - So this surface here could be an unconformity surface?) If something else were deposited on top of it - right here we don't have anything else deposited on top of it - we see these occasional little boulders on top and if you go look on the top of Glade Hill there's a nice layer of boulders over there.) Let these people through and we'll continue our discussion.

Migmatite - partially molten - Jill. Um - migmatite. What can we do with igneous rocks, like we did with the lamprophyre? Isotopic dating. So we can isotopically date this granite. It turns out this granite gives us an age of 460 million years ago. Same age as the metamorphism – same orogeny. The Taconian Orogeny heated up these rocks and squeezed them. What was the cause of the Taconian Orogeny? The collision of a volcanic island arc with North America. So, good work guys! Isn't this a spectacular rock?!!

I have traipsed across this old planet a fair amount and I've seen migmatites in only two places. I've seen them up in Maine, and I've seen them here. So, you're really lucky that you're taking a Geology class where you're really close to a place where you can go and see a migmatite. Most students are not that lucky. OK!

He's showing us the difference between fresh and weathered metagreywacke - Jill - he's showing us... we just looked at the migmatite.

By the way the smell you smell right here is sulfur. This is a creek here that evidently ...some sort of pyrite deposit. There's iron in the creek which is rust - iron oxide. And, it smells sulfurous. Remember that pyrite is iron and sulfur. Here, it's being broken down here by the water.

Is that why they have the ridges here in general? - student. Ridges - Jill Ridges of quartz extruding out of mica. - example/observation

Remember I showed you that image of the scuba diver and he's standing in the river and the sea level is rising over him. OK, this is the river gravel that was deposited in that river. It's part of the Weverton Formation - it's early Cambrian. It's about 540 million years old or so. And again, I wouldn't expect you to know that by just looking at it. I only know that because I walk around thinking about geology a fair amount and I recognize it here. So, I'm correlating this boulder with outcrops to the west. There's some other boulders here as well. As well as this reddish stuff. There's these reddish sandstones. We're going to talk more about those just over the hill here. Here is a nice example of diabase which is going to be related to this red sandstone. This is a mafic igneous rock because I don't want to give away what I'm about to reveal down the trail. But, there is a variety of boulders here. All of these boulders can be sourced to outcrops in the west. Again, more evidence that the Potomac River is being pulled from the west to the east over time, carrying sediments along to prove it. OK? Like little passport stamps telling you where it's been. OK, a little bit further and we've got two more boulders to look at.

Three different sandstones. I've got samples from all three of them here. Somebody tell me the name of one of these sandstones. Quartz sandstone - the white one, almost pure quartz. The other is greywacke - dark grey - that's what the local bedrock was originally. This rock (sample) is a greywacke, not a metagreywacke - these (bedrock) are metagreywackes. The pinkish one is arkose. It's a mixture of sand, mud, and potassium feldspar. Big angular pieces of potassium feldspar. The kind we saw in that granite. In terms of maturity, the arkose and the greywacke are immature sandstones, and the quartz is mature sandstone. We've already learned that the greywacke is deposited in deep sea fans, sometimes called abyssal fans or submarine fans. Where is quartz sandstone deposited? Beaches, good. And where is arkose deposited? Very immature, it still has all its feldspars it hasn't broken down to clays which means it hasn't come very far. Rift valleys. Arkose is a characteristic of rift valleys.

We have two boulders here which can help complete our sandstone triumvirate. We've already got the greywacke down - check that off the list. This one here is a metamorphosed quartz sandstone, so its made out of quartzite. It's a really interesting one. Do you see those little circles on top of it? Those are the tops of fossilized worm burrows. These fossil worm burrows project down into the rock like this. They're cylindrical; called Skolithos. Some of you have noticed Skolithos trace fossils in lab. I've got a few samples out on the countertop. They look like little soda straws running through the rock. Again, I know where that came from. It's from the Antietam Formation. That's a barrier island beach sand that's found in the – the river has traveled from the west to the east - all the others boulders I've stopped to talk about have been located in the Blue Ridge. This is also a Blue Ridge rock. The Antietam National Battlefield is what its named for - the Antietam Formation. Characterized by these little fossil worm tubes.

This red beauty right here, and I encourage you to do so, - these little pink specks are potassium feldspar. This is an arkose. A big beautiful arkose from 10 miles away. This naturally outcrops 10 miles from here. 10 miles upstream at a place called Seneca Creek. Because it outcrops at Seneca Creek we call this the Seneca Sandstone. Seneca sandstone is an arkose. So, Michael found a piece of this early on. We've been walking over various boulders of it all along. Its source is so close by we actually have a lot of it here. What else have we seen that's red sandstone today? The first stop we made - along the canal. The locks were made out of this red Seneca sandstone. It turns out to be a great building stone. This Seneca sandstone is quite young. Because its young, its actually younger than Appalachian Mountain building. Which means it hasn't been metamorphosed. So, it's essentially, it's wet, poorly-lithified sand. So that means that when you cut it out into blocks, it cuts like butter. But, then once you take it out, it dries out, and once it dries out it becomes much harder. That's the ideal building stone. Easy to extract from the ground but hard once you make something out of it. The Smithsonian castle is made out of red, Seneca Sandstone. The "brown"stones in Dupont circle, too...

This is a very interesting chapter in Geologic History because, as Laura pointed out, arkoses get deposited in rift valleys. We've talked about putting Pangea together, killing the Iapetus Ocean through continental collisions, but we all know that Pangea didn't last. Pangea broke apart, and when it broke apart, what opened up? Rift valleys. Some of those rift valleys filled in with sediment and they didn't keep opening. Some of the rift valleys connected together and became a new ocean basin called the Atlantic Ocean. This is from the site of a failed rift. The rift began to open, but it didn't keep opening. It is located to the west of here, called the Culpeper Basin. The Culpeper Basin is a Triassic aged rift valley. When Pangea was breaking apart this big gaping hole opened up in the crust filling in with immature sediments like this arkose and then it stopped. That's where you find Dulles Airport today - it's in the middle of the Culpeper Basin. But, some other rift valleys, over in that direction (east) connected together and they were the weakest link. That's where the crust kept ripping over there. And it ripped and it opened wider, and wider, and wider and eventually sea water came in and it became a little ocean basin and then it widened and widened and widened and its still widening today. And, that's the Atlantic Ocean. So, basically that process began around 200 million years ago in the Triassic, and this is a Triassic sandstone. What organisms were alive during the Triassic? Dinosaurs.

--- T R A N S C R I P T --- E N D S ---

If you've made it to the end of this post, congratulations! I'm sorry, but I won't be able to refund the hour you just spent reading it... But since you're here, I'm interested in your feedback about this -- what elements you read about here caught your attention? Why? Thanks...

Labels: field trips, nova, piedmont, teaching

NOVA recently updated their webpage, and now we have a big banner photo which changes every time you hit "refresh." A colleague pointed out that there's an image up there of the Snowball Earth field trip last summer:

I think it's safe to say that now John, Judy, David, Jay, Sam, and I are officially B-list celebrities...

Labels: field trips, nova, snowball earth, teaching

The NOVA Geology Department has organized a Wilderness First Aid (WFA) Training Session for May 22-23 here on campus. Our goal is to give our field trip leaders (geology and otherwise) the skills they need to handle medical emergencies. If you're interested in getting WFA Training, please join us. The cost for the 2-day certification course is $250. Contact Nancy Chamberlain for registration information.

Labels: field trips, nova

Being outside with my students last week was great. Now that the weather is warming up, I'm looking forward to the start of "field trip season," which for me starts next week. This photo (by a friend of a friend) summarizes my attitude towards field trips:

My translation: "Field trips! Cue the singing angels! It's great to be outside! It's great to be a geologist! It's great to live on planet Earth! Love it, people: Play on your planet! Get out there and experience the one & only planet that you will ever know!"

Labels: field trips

I've already introduced you to two of my Honors students' field projects. Now for the last of the three -- Jason's project on the strained metaconglomerate of Klingle Road. Klingle Road is a "road" in D.C. that was damaged by a storm some years back, and never repaired. Some people have started using it as a park, while others clamor for the road to be fixed. Geologically, it's interesting because it exposes a rock unlike any other nearby: a distinctly foliated metaconglomerate. Because I am so clever, I call it the Klingle Road Metaconglomerate. It's part of the "Laurel Formation," which is one of many flavors of metagraywacke / accretionary wedge complex that make up the bulk of the Piedmont in this area. Here's some of the squished clasts that Jason is interested in:

We know these rocks got heated up a fair bit. How do we know this? Well, they flowed out into elongated shapes all oriented in the same direction for one (see the additional photos here). The outcrop is peppered with clusters of little plus-shaped protuberances: they are clusters of sericite (cryptocrystalline muscovite) in the shape of staurolite porphyroblasts. Staurolite is a reasonably high grade metamorphic mineral, and when we see the three-dimensional shape of staurolite, but it's been turned into relatively-low-grade sericite, it's an indication of "retrograde metamorphism." Basically, after hitting the peak of its particular metamorphic conditions (high temperature and pressure, growing staurolite), the rock is readjusting to lower temperatures and pressures, and those staurolite crystals are reacting to a mineral that's more stable at those lower temperatures and pressures: sericite.

But anyhow -- back to the metaconglomerate. It's made of clasts, and those clasts have been stretched. The question is: how much have they been stretched. Sometimes when strain estimates are made, we assume an initial sphere shape, and then measure the lengths of the various axes of the resulting ellipsoidal shape (the "strain ellipsoid"). But is the assumption of initial sphericity valid? Jason is testing this issue by measuring the axes of cobbles and pebbles from the metaconglomerate as well as loose cobbles and pebbles found in nearby Rock Creek. We want to get a sense of how ellipsoidal cobbles are before they experience orogenic shortening/stretching. Here's a shot of Jason, Spencer, and Victoria measuring cobble axis lengths on a gravel bar near the National Zoo:

And a shot of the crew close-up:

And, just for fun, here's one more shot from Victoria's field area on Broad Branch. We hiked up to the contact with the Kensington Tonalite (a ~464 Ma felsic intrusive rock -- essentially a granite) and found a series of small waterfalls over this resistant rock unit. In the sequence of cascades were a series of deep pools. I submerged myself in one of them:

Labels: appalachians, dc, field trips, nova, piedmont, sediment, structure, teaching

Last Friday, I had a fun local field trip, in search of ultramafic rocks included in the Piedmont's metamorphosed accretionary wedge complex. My companions on the trip were David and John, both of whom are retired gentlemen pursuing geology as a hobby. Because they're doing geology for fun, they are among the most dedicated and interested students I've met at NOVA. Friday's trip was something I've been meaning to do for a while, and both of them thought it sounded like an eye-opener, so they came along too.

Our goal was to find some new outcrops that we hadn't seen before. Of primary interest were several mafic and ultramafic bodies included in the larger metasedimentary complex of rocks that we know today as the Piedmont. As I've mentioned before, these Piedmont rocks are interpreted as being the rocks of an ancient (Neoproterozoic - Paleozoic) ocean basin. When the ocean basin closed during Appalachian mountain-building, the sediments of the ocean got squished and squeezed between North America and Africa. Mixed in with them were chunks of the ancient Iapetus Ocean crust, which would probably be recognizable as ophiolites if it weren't for that pesky regional metamorphism they endured as a result of the collision. Up and down the east coast, there are outcrops of these mafics and ultramafics along the presumed "suture" zone between ancestral North America and terranes (blocks of crust) that were once a volcanic island arc in the Iapetus Ocean. As with most geology field trips, we also found some other stuff worth noting, even though it wasn't our primary objective.

Our first stop (located thanks to Diecchio & Gottfried (2004) in USGS Circular 1264) was in Clifton, Virginia, where we went to see the unconformity between the Piedmont metamorphic rocks and the Triassic sedimentary rocks which overlie them in an ancient rift valley called the Culpeper Basin. Tragically, instead of a beautiful outcrop, we found freshly graded surfaces and several new McMansions. There was only a small strip of undeveloped land, about 20 feet wide and 50 feet long which had any rock left. But in that area, we found an outcrop of soapstone. Here, John scratches the soapstone (talc) with his fingernail. It's soft!

In this case, the soapstone is interpreted as being metamorphosed ultramafic rock. Close to it, we found this piece of conglomerate:

The conglomerate is the base of the sedimentary sequence in the Culpeper Basin: it's the Reston Member of the Manassas Sandstone Formation. Notice that it contains clasts of foliated metamorphic rocks -- these were derived from the older Piedmont rocks it unconformably overlies. The Piedmont rocks got metamorphosed during Appalachian mountain-building, and then when Pangea broke up, the Culpeper Basin (one of the Newark Supergroup basins) opened up and got filled in. The source for the infilling sediment was the neighboring area, not surprisingly including pieces of the Piedmont. Up-sequence, the conglomerate is overlain by the regular Manassas Sandstone, which is a rich brick red in color (classic Triassic red beds), and contains a wealth of primary sedimentary structures. I found this one piece, which unfortunately broke into chunks when I picked it up:

It displays ripple marks, raindrop impressions, and a few horizontal branching trace fossils. Anyhow, that was about it for the Clifton stop. We were bummed about the development destroying the outcrop. On to the next location, Indian Run, on the east side of Annandale. There, using the geologic map that accompanied Drake & Lyttle (1981), we walked along the creek bed looking for exposures of rock. We didn't have to go far before seeing some heavily-rusted green rocks:

The above photo is dominantly chlorite, but check this out:

Pyroxene-rich inclusions (xenoliths? olistoliths?) were observable in the heavily-weathered exposures. The outcrops here were saprolitic, meaning they were essentially "rotten rock." David was struck by how soft they were. He said "It feels like velvet!" We turned our attention to the more coherent specimens which were weathered out and deposited as cobbles in the streambed. I got a watermelon-sized specimen that's about 40% massive peridotite and 60% greenschist. (I showcased this leprechaun-colored specimen last night in Historical Geology lecture, when we were discussing the Taconian Orogeny.) We also found intriguing hints of mountain-building in clasts like this:

That's a couple of beautiful folds in gneissic metamorphic foliation. As above, the bright green minerals are chlorite. We also found some cobbles of sedimentary rocks mixed in with the locally-derived metamorphic rocks. For instance, here's a nice semispherical cobble of flint, likely derived from the flint-bearing limestones of the Shenandoah Valley:

How did this flint nodule travel ~50 miles from its source area to its current resting place in Indian Run? Likely, it was transported by an ancestral version of the Potomac River, which brought many westward-derived cobbles eastward during the Cretaceous. About 100 million years ago, this river deposited a layer of cobbles all over our local area, preserved today as the Potomac Formation. It unconformably overlies the Piedmont rocks, and can be found today as the basal layer of the Coastal Plain. It's even found as a layer topping our highest local hills. The exposures in Indian Run actually offered a nice view of the unconformity surface, with foliated metamorphic rocks below, and unlithified Cretaceous gravel deposits on top:

Just to close out this post, I'll show a few other cobbles found in the streams. Here's a gneiss containing big, beautiful porphyroblasts of garnet:

And here's a Skolithos-bearing boulder of the Antietam Formation (quartz sandstone / quartzite), which I originally posted a few days ago, but is so gorgeous it should be shown again if I'm talking about boulders.

Finally, as a preview of tomorrow's post, I'll show a boulder which hints at the complex relationship between the foliated metamorphic rocks (gneisses) of the Piedmont and felsic igneous rocks (granites) which were derived from the partial melting of the gneiss. In other words, this is a boulder of migmatite: rock that has experienced partial melting. We'll explore this in more depth with some in situ photographs tomorrow.

Labels: appalachians, culpeper basin, field trips, flint, geology, nova, piedmont, unconformities, virginia

Picking up with my series of posts introducing the work my Honors students are doing this semester: today we'll take a look at Spencer's project, which involves field work on a bedrock terrace (strath) of the Potomac River near Chain Bridge (which can be seen in the background of this photo). As before, ignore the datestamp in the lower-right of the photo. These pictures were taken last week, not in 2004.

This is in the westernmost corner of DC's "diamond" shape. The bridge leads across the river into Arlington, Virginia. As you can see, there's a lot of rock exposure here -- the sort of thing we go crazy over here in the east. As noted before, this is metagraywacke (sometimes metamorphosed to schist, sometimes to gneiss, sometimes just strongly foliated, and sometimes so lightly metamorphosed / deformed that it even preserves original sedimentary structures like graded bedding. The interesting thing about the Chain Bridge locality is that in amongst the metagraywacke are big chunks of other rock types. I'll refer to these as "clasts." Some geologists have interpreted them as sedimentary deposits; others as "olistoliths" (tectonically emplaced chunks in an accretionary wedge complex). Spencer is in charge of documenting the variety of these clasts, in hopes that it may tell us something about their ultimate source. Here's a big elongate clast of gneiss:

We had a good little field routine going: Victoria and Jason would go scout out clasts, and then mark their location with a chalk arrow. Then Spencer would document each clast's lithology and characteristics (e.g. foliation at an angle to regional foliation) and then photograph it. Once he'd photograph it, he "checked it off" with chalk. All of this chalk graffitti gets washed away with the next big rainstorm.

Some of the clasts are no longer in their original condition. The one below, for instance, bears a multitude of garnets, metamorphic minerals which reflect how the clast's original composition reacted to the higher temperatures and pressures of Appalachian mountain-building.

Another thing we saw a lot of in the Chain Bridge locality is erosional features related to the incision of the Potomac River into bedrock. Here's Jason showing off a pothole that drilled all the way through one outcrop:

Next time, we'll take a look at Jason's project.

Labels: dc, field trips, geology, nova, sediment, teaching

Here's a view in the creek bed of Spencer and Victoria looking for kink band outcrops. (Ignore the date stamp in the lower right: it is not accurate.)

A nice kink band. Width of photograph is ~25 cm.

Victoria takes the strike of the metagraywacke's foliation:

Here's a Z-fold in the foliation -- more of a kink "knot" than a kink band. The kinematic sense of motion in this photo is top-to-the-right (right-lateral):

Here, Jason and Spencer measure the orientation of a kink band:

A nice little outcrop of crenulation cleavage, showing porphyroblasts of chlorite (green/blue) and garnet (red/brown). The pencil is parallel to crenulation "wrinkles".

Next time, we'll take a look at the projects that Spencer and Jason are working on.

Labels: field trips, geology, nova, sediment, structure, teaching

I'm also psyched about joining NAGT's ranks because they offer a series of grants. Getting small educational grants is my new hobby, so I'm looking forward to making some good stuff happen at NOVA with some sum from NAGT.

Labels: conferences, field trips, google, msse, teaching