NOVA Annandale | Geology | Bentley | Snowball Earth GOL 299: Snowball Earth

In Summer 2010, I will again be offering a "Supervised Study" course examining the Snowball Earth hypothesis.
See photos from the Summer 2007 class here.

GOL 299 SNOWBALL EARTH. (2 credits) The Pleistocene Ice Age was the proving ground for our species. But an earlier episode of glaciation, dubbed Snowball Earth, may have provided for the evolution of multicellular animals and plants. The Snowball Earth glaciations certainly stretch our conception of what the limits of climate change are: the ice 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 geologic, chemical, and biologic evidence for Snowball Earth, and includes a field trip to local Snowball glacial deposits. Course meets four times: three evening sessions (6pm-9pm) 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

READINGS WILL BE OFFERED ONLINE FOR REGISTERED STUDENTS AT: http://learn.vccs.edu/

Diamictite of the Fauquier Formation, northern Virginia. Note the large variety of clast sizes and shapes, and the dark color. These have been interpreted by some geologists as possibly being glacial deposits under low oxygen conditions. Pole is divided into 10-cm scale bars. Photo courtesy of Jay Kaufman, University of Maryland.

A large clast of granite gneiss (the Grenville-Orogeny-aged "basement rock" of the Blue Ridge), truncating some finer-grained layers and flattenening the layers below it. This relationship between the large clast and the matrix suggests it may be a dropstone, a iceberg-rafted clast. Hammer for scale.

Red beds, of the Fauquier Formation, indicating higher oxygen levels than the lower strata. These beds are stratigraphically above the diamictite. Hammer for scale. Photo courtesy of Jay Kaufman, University of Maryland.

Contact between the marble (uppermost Fauquier Formation) and the overlying lavas of the Catoctin Formation. Some workers have interpreted this as a "cap carbonate" which was deposited at the end of the Snowball Earth glaciation. Visible on the far right is flange of of carbonate poking upward into the Catoctin meta-basalt. This suggests a "flame structure" to some workers, who infer that such soft-sediment deformation would indicate that the lava of the Catoctin Formation may have flowed out over damp, unlithified carbonate sediments. As we will learn, volcanic eruptions are implicated in ending the Snowball Earth glaciation. Hammer for scale. Photo courtesy of Jay Kaufman, University of Maryland.

Contact between the "cap carbonate" and the overlying Catoctin lava flows, showing the putative chill zone developed along the bottom of the lava flow. Hammer for scale.

As above, another exposure of the contact (dark) of the Catoctin Formation where it comes into contact with the Faquier Formation's "cap carbonate" member.Pen for scale.

Dropstone in the Konnarock Formation, another alleged Snowball deposit in southwestern Virginia. This is one of the samples that Snowball students will examine in lab. Penny for scale.

Another dropstone in the Konnarock formation. Note the downward deflection of the lower laminations (thin layers) indicating the dropstone pressed down from above. This dropstone is a piece of the Mount Rogers Formation rhyolite. It is also one of the samples that Snowball students will examine in lab.Penny for scale.

Diamictite of the Konnarock Formation. Unlike the above two samples, this diamictite lacks thin layering, and is instead a massive jumble of many different sized sedimentary particles. This is one of the samples that Snowball students will examine in lab. Penny for scale.

Additional details:

Readings:

Snowball Earth, Gabrielle Walker (2004)
"Late Proterozoic Low-Latitude Global Glaciation: The Snowball Earth," Joe Kirschvink, in The Proterozoic Biosphere, Schopf, J.W. & Klein, C., eds., pp. 51-52, Cambridge University Press, Cambridge (1992).
"The Snowball Earth," Paul F. Hoffman and Daniel P. Schrag, (1999).
"Dynamic Earth, Permissive Ecology," Chapter 12 of Life on a Young Planet, Andrew H. Knoll (2003)
"Red Earth, White Earth, Green Earth, Black Earth," Joe Kirschvink, Engineering and Science magazine, #4 (2005)
"Snowball Fights," Naomi Lubick, Nature 417 (2002), pp.12-13.

Laboratory:

Examination of:
BIFs, tillites, glacial cobbles
Neoproterozoic Konnarock Formation deposits from southwestern Virginia, near Mt Rogers.
Neoproterozoic Fauquier Formation deposits from northern Virginia, near Aldie, VA.
"Snowball Suite" rock samples from Namibia, Greenland, NW Canada, and Mauritania.

Field trip:

Neoproterozoic Fauquier Formation deposits, Blue Ridge Province north of Aldie, VA & contact with overlying Catoctin Formation (metamorphosed flood basalts).

Some of the topics to be covered:

Timing and extent of Proterozoic glaciations (several episodes)

Geological evidence
Distribution (global): Marinoan, Sturtian, and Ediacaran glaciations
Dropstones
Tillites
Glacial striations
Stratigraphy: tropical limestone/tillite/tropical limestone (cap carbonate)
Paleolatitudes and paleomagnetism (the fold test)
Sea-glacier dynamics and tropical sea-ice thickness

Chemical evidence
Reducing/oxidizing atmosphere
Rise in oxygen: 3 stages, separated by 2 snowball Earths
BIF/red bed transition and 700 Ma BIF “blip”
Glacial anoxia
Iron-manganese formations
Isotopes
Carbon isotopes and stratigraphic correlation
13C

Causes and effects
Trigger? (Causes)
Albedo and positive feedback loop
Ending Snowball Earth
Geochemical carbon cycle and global climatic stability
Massive greenhouse effect due to volcanic CO2
Glacial meltdowns and cap carbonates
Effects on living organisms
First metazoans

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