21 April 2013
Three new GigaPans I shot last Friday east of Staunton, Virginia, at a semi-legendary exposure behind the Sleep Inn at the 250 / 81 intersection.
Students: Which way is up? Which criteria did you use to make that determination?
gigapan, ordovician, primary structures, sandstone, shale, valley and ridge, virginia
The top of this GigaPan is up because the trees and bushes are negative gravitropes.
I thought the sky was a dead giveaway … 🙂
Seriously I’ll take a stab and say right side is up. Vertical bedding indicates a 90 degree rotation and sandstone overlays shale.
You guys are hilarious.
To clarify: STRATIGRAPHIC up…
You might base your assessment on primary sedimentary structures, or perhaps on deformational structures. Either one will get you there.
Here goes nothing.
Left is up. Cracks, fissures, and “jumbled” looking beds in the bedding planes almost look like they get wider toward the left, until they abruptly disappear. As if something created them and then allowed the elements to work downward into the stack, only to be covered by additional layers of sediments, afterwards.
That’s my story and I’m sticking to it, despite the fact that I have no idea what I’m talking about.
Left is stratigraphic up. The cleavage tells the tale! A few m left of the leftmost exposure, there is this:
We’re looking at the east side of a syncline here.
> Left is stratigraphic up. The cleavage tells the tale!
Forgive my lack of savvy, but does that mean my supposition was maybe just a little bit correct, or am I still wandering in the wilderness with neither map nor compass?
Apologies for the less than astute understanding of things geologic, and a thousand and one thanks for putting this stuff out there for one and all to thoroughly enjoy.
Actually, I’m not sure I totally understood what you were getting at. But, that being said, there “should” be a primary sedimentary pattern of graded bedding here: with beds starting abruptly on the right, then gradually transitioning to finer grained sediment as you go left, to end abruptly at the bottom of the next bed “up.” The cleavage (“cracks, fissures”??) is way better developed in the muddier layers, and not in the sandier layers beneath them.