Posted by: Alan Pitts | March 12, 2012

Two for One: Fold (on a fold) and Fossils

Here are a few photos of some really neat ( and when I say neat I mean totally awesome) folded sedimentary strata from the Valley and Ridge province in West Virginia. The work I’m doing in WV is part of a larger and really cool project I’m working on with Callan Bentley named MAGIC, or the Mid Atlantic Geo-Imagery Collection. As geologic MAGIC workers our goal is to build a massive online collection of geo imagery to share with people like you (student/amatuer/professional consumers of online geologic information) to enjoy, investigate, and learn from. Right now my contribution to the project is a job of searching for the best outcrops around and recording them in all their brilliance using GigaPan photography.

This location is a prime road side stop if you happen to be traveling along the new Route 55 ( also known as Corridor H) in West Virginia. This enormous strip of asphalt, blasted through miles of pristine beautiful WV mountainscape, happens to reveal some of the best exposures of lower Paleozoic sedimentary strata anywhere in the mid-Atlantic region.

Here is a photo of the locale along with my initial interpretation annotated.

I think this is part  Tonoloway Formation, a Devonian tidal carbonate unit.

For a better look at this outcrop and the complex folding, please go take a look at the Gigapan I took of this location, wordpress wont let me embed it here, so until I figure a way around this, links will have to do. Using the gigapan as an investigative tool from home, My friend Aaron and I identified several folds in the “I have no idea” section  that are worth taking a look at. (Make sure to use the zoom controls to get up and close with the outcrop!)

These folds are outcrop-scale expression of the intense regional deformation experienced by these rocks during ( most likely) the Alleghenian Orogeny, when Africa collided with North America to create Pangea.

While the Gigapan robot was doing its job of systematically guiding the camera through 170 photos to build the stunning Gigapan of this location ( which if I may reiterate, you should really go see…..please) I walked across the highway to inspect the outcrop.

On the ground I found this sample littered with tiny lentil-shaped fossils. These are Ostracods, most likely Leperditia, arthropods which were quite abundant during the  Silurian-Devonian.

I also found this sweet hand-sample-size parasitic fold.

Here is another version of the image with some annotations to highlight the folding.

As if this fold on a fold wasn’t awesome enough, I think I found some fossils on it too. Do you see them? It wasnt until I was back home looking at my photos that I noticed them, but I think there are some more Ostracods in the upper left corner.

Here

Looks like some more little lentil shapes which are lighter in color than the surrounding rock.

As you can see in the middle-right of the photo that this fold, along with the rest of the surround rock is weathering at a rapid rate. Without much encouragement, this guy basically fell off the wall and into my hands. So I brought him home.

Here are a few more pictures of the fold once I cut it at the GMU rock saw room.

Here is the original face, rotated 180 degrees from the original orientation ( upside down).

Now here is the other side which was cut:

When this guy came out of the rock saw, Aaron and I simultaneously let out an uncontrollable “Whooooooaaaa!!!” lasting for nearly 10 seconds. It was a really funny moment for us and one in which we realized that we are both certified geology nerds. You just can’t fake that kind of excitement.

One of the other things I found, while inspecting this rock on all sides, was some great slickenlines. Slickenlines are tectonic structures which form as rocks slide past each other. Slicks as they are commonly called, are useful structures for understanding motion along faults and slippage planes. In this case,these slicks were formed as “flexural slip”.  Flexural slip occurs as sliding along bedding planes as a result of folding. I found this diagram on flexural slip to help explain the process ( and to help me finish the post sometime soon).

Here is the same image from above with some lines and arrows to mark the direction the adjacent rock was moving.

I always enjoy rock samples with multiple subjects of interest. This one is loaded with fun structures that I was able to identify myself and Im sure if/when I show this to some of my geology advisors and collaborators that they will find more. What do you see here ? Anything that you find interesting I missed? I’d be happy to hear any alternate interpretations.

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