Oncolites
A block and half away from my new condo, there stand a trio of imposing churches, at the corner of 16th Street NW and Columbia Road NW. A Google Map of the corner in question:
The one I want to discuss today is on the southwestern corner of this intersection. It's currently a Unification Church, but the structure was built in 1933 as the first chapel of the Church of Jesus Christ of Latter Day Saints (the Mormons) in DC. According to Chris Barr, an attorney and amateur paleontologist who is compiling an "Accidental Museum of Paleontology" about DC's building stones that include fossils, "two grandsons of Brigham Young contributed to its design and artwork, and the church consciously echoes the design of the Mormon Temple in Salt Lake City." Not only that, but they opted to use exterior buuilding stone shipped in all the way from Utah!
Chris's website about all the fossil-containing DC building stones is nearing completion, and I will post a link here when it is live. In the meantime, I wanted to share some of the information he compiled about the rocks which makes up the exterior of the Unification Church: Utah Bird's Eye "Marble."
Here's what it looks like:
The elliptical shapes you're seeing here are oncolites (sometimes called "oncoids"), and they are essentially little ellipsoidal stromatolite balls. A little grain of this or that gets encrusted by calcifying algae / microbial slime, and layer upon layer gets added with addition growth of those slime layers, growing up through the calcite they trap. It's not a true marble, in other words: it's a limestone.
These limestones with oncolites originated in a large freshwater lake called Lake Flagstaff, approximately 66 to 58 million years ago (Paleocene). The lake was present in northeastern and central Utah. According to Chris Barr, the stone used on the exterior of the Unification Church was quarried at "8,000 feet in elevation, in what is now the Manti-La Sal National Forest in the mountains more than 60 miles south of Salt Lake City."
Some of them have partial void spaces internally, which have since been filled by sparry calcite:
The horizontal layering of the non-spar gunk inside these voids provides a little paleo-horizontal "level" to help reconstruct which way was "up" when these sediments were deposited. (This particular block is on its side in the wall of the church; I've rotated the photo to paleo-up using Photoshop. (That's also where the arrows come from!)
For some perspective on the recent history of the building where these cool rocks are displayed, I'll quote from Chris Barr's soon-to-be-released website: "Changes in the neighborhood, the growing needs of the Mormon community, and the prospect of costly repairs to the walls, led to the end of services in 1975 and the sale of the chapel, which was purchased by the Unification Church in 1977. The Mormons constructed a new, larger chapel in suburban Bethesda - a structure that also provides a visible reference to the temple in Salt Lake City."
The one I want to discuss today is on the southwestern corner of this intersection. It's currently a Unification Church, but the structure was built in 1933 as the first chapel of the Church of Jesus Christ of Latter Day Saints (the Mormons) in DC. According to Chris Barr, an attorney and amateur paleontologist who is compiling an "Accidental Museum of Paleontology" about DC's building stones that include fossils, "two grandsons of Brigham Young contributed to its design and artwork, and the church consciously echoes the design of the Mormon Temple in Salt Lake City." Not only that, but they opted to use exterior buuilding stone shipped in all the way from Utah!
Chris's website about all the fossil-containing DC building stones is nearing completion, and I will post a link here when it is live. In the meantime, I wanted to share some of the information he compiled about the rocks which makes up the exterior of the Unification Church: Utah Bird's Eye "Marble."
Here's what it looks like:
The elliptical shapes you're seeing here are oncolites (sometimes called "oncoids"), and they are essentially little ellipsoidal stromatolite balls. A little grain of this or that gets encrusted by calcifying algae / microbial slime, and layer upon layer gets added with addition growth of those slime layers, growing up through the calcite they trap. It's not a true marble, in other words: it's a limestone.
These limestones with oncolites originated in a large freshwater lake called Lake Flagstaff, approximately 66 to 58 million years ago (Paleocene). The lake was present in northeastern and central Utah. According to Chris Barr, the stone used on the exterior of the Unification Church was quarried at "8,000 feet in elevation, in what is now the Manti-La Sal National Forest in the mountains more than 60 miles south of Salt Lake City."
Some of them have partial void spaces internally, which have since been filled by sparry calcite:
The horizontal layering of the non-spar gunk inside these voids provides a little paleo-horizontal "level" to help reconstruct which way was "up" when these sediments were deposited. (This particular block is on its side in the wall of the church; I've rotated the photo to paleo-up using Photoshop. (That's also where the arrows come from!)
For some perspective on the recent history of the building where these cool rocks are displayed, I'll quote from Chris Barr's soon-to-be-released website: "Changes in the neighborhood, the growing needs of the Mormon community, and the prospect of costly repairs to the walls, led to the end of services in 1975 and the sale of the chapel, which was purchased by the Unification Church in 1977. The Mormons constructed a new, larger chapel in suburban Bethesda - a structure that also provides a visible reference to the temple in Salt Lake City."
Labels: dc, limestone, paleocene, primary structures, utah
6 Comments:
Wow, those are beautiful!
Thanks for reminding me of the difference between oolites and oncolites. We saw some magnificent examples of the latter somewhere south of Death Valley in Cambrian limestone, but sometime in the last 25 years, the distinction between the two had become muddled in my head.
Excellent photos of oncolites!
interesting grain size distribution. there seems to be a bimodality in the coarse grain fraction, a sandy fraction and a gravel fraction (the oncoids). may be a good example of how in situ growth of grains and not necessarily hydrodynamic sorting may play a significant role in size distribution of sediments.
Gorgeous!
Re: the little sediment-levels (geopetal structures); I remember one of my undergrad professors running an exercise where he went through our class of 20+ students and made each of us name a different way of determining "stratigraphic up". I remember sweating bullets as my turn got closer, hoping no one would name the two or three that I could think of. He went through all of us at least twice before we finally ran out of ideas.
--Howard
Here's another interesting picture of oncolites from the flicker site
http://www.flickr.com/photos/greenriver/419430313/
Post a Comment
<< Home