16 September 2011
Friday fold: Pinelog Formation
Posted by Callan Bentley
Reader Jacob Langseth sent in this image of a lovely fold that he recently saw in the Blue Ridge province of Georgia. It’s located in an old CCC rock quarry, off of the Pine Log Creek Trail system, in Bartow County.
You can click on that first image to make it bigger and see a bit more context. Nice differential weathering, eh?
…Or you can just keep scrolling down, to see the (obligatory?) annotated version that I whipped up:
I consulted with the reigning queen of Georgia geology, Pamela Gore of Georgia Perimeter College, and she was able to shed a little more light on this feature… She’s just finished writing a new book, The Roadside Geology of Georgia, with co-author Bill Witherspoon. Both of them were kind enough to spend a bit of time identifying Jacob’s fold. These rocks are identified as “pp3” (phyllite and quartzite) on the extant state map, as Pinelog Formation on Tull GGS 2007, and as Wilhite Formation undivided on Thigpen & Hatcher’s 2009 Western Blue Ridge GSA Map and Chart MCH097 compilation. Thanks to Pamela and Bill for sharing their expertise.
And: Thanks for sharing this, Jacob! I welcome other reader contributions for the “Friday fold” series. Just shoot me an e-mail. Include any relevant details that you’re aware of.
[…] The sample is a chunk of metasedimentary Streamstown Formation, one of the formations in the Neoproterozoic Argyll Group, part of the Dalradian Supergroup of western Ireland. The next formation down in the stack is a quartzite; the Streamstown is overlain by the gorgeous Lakes Marble. You can see how weathered it is – with the pelitic layers (formerly muddy bits) weathering out more rapidly than the psammitic layers (formerly sandy bits). We saw similar differential weathering last week in a Friday fold from Georgia. […]
I’ve noticed this rock, and even having zero knowledge of geology, it caught my eye as something I’ve never seen before. I’ve got a few other pics in Google photos of it also. When I first ran across it, I thought it might have been some sort of petrified wood, simply because of the wood grain like pattern.