7 June 2010
I spent last Thursday on a long field trip in the Valley and Ridge province of northernwestern Virginia. Leading the trip was Dan Doctor of the USGS-Reston. Accompanying Dan was a UVA environmental science student named Nathan. And the NOVA crew rounded it out: professor Ken Rasmussen from the Annandale campus, associate professor Victor Zabielski from the Alexandria campus, and me. We met at the Survey at 9am, and headed west towards Strasburg, site of my Massanutten field trip.
We started off by examining three Ordovician carbonate units (all above the Knox Unconformity) on the I-81 exit ramp at Route 11. This is the same sequence seen at the classic Tumbling Run outcrop: the New Market limestone, the Lincolnshire limestone, and the overlying Edinburg Formation. We looked at fossils, stratigraphy, some minor structures, and some interesting lithified gunk on the inside of some solution cavities (small caves). Dan interpreted it as collapse breccia: lithified sediment from inside the cave. The question was: when did it form? We wrestled with the best way to test its age, and didn’t come to any clear conclusions. I love moments like that one: out in the field, one geologist shows another something that’s caught his or her attention, and the other geologist reacts, and the two toy with the idea, batting it around like a cat with an unknown object. Like the cat, geologists will either then get really excited and attack the new idea, or get bored, shrug, and walk away.
Our next stop was Crystal Caverns, a commercial cave that is in ownership limbo. Our spirited guide Babs said that it was likely the last time she would lead a tour down in the cave. She was busy liquidating the artifacts of the adjacent Stonewall Jackson Museum, which had recently been shut down by its board of directors. The cave is accessed via a small building that has been built over its mouth. It was a cool cave with a significant 3D aspect: we descended in a corkscrew like fashion, then came back up via a different route. Very cool. A shame that it is being closed (at least temporarily) to the public.
We followed the cave with lunch at a local Mexican restaurant, and while we were there, a big thunderstorm rolled through. Victor, Dan, and I played dueling iPhones to get imagery of the weather front and plot out our plan for the rest of the afternoon.
The afternoon was spent visiting outcrops on the west side of the Great Valley, working our way up to Route 50, and then west to Gore, VA. I wasn’t especially fastidious about photographing everything we saw, but here’s a sample of where I opened the camera shutter…
Ooids in the Conococheague Formation:
Same shot, zoomed in to the middle:
Fossil (blastoid? crinoid?) stem, Needmore Formation:
There were some lovely Opuntia cactus blooming among the vetch at this Needmore outcrop:
From there, we checked out the Chaneysville Member of the Mahantango Formation, where we saw some snail fossils…
…and some spiriferid brachiopod fossils:
Our last stop of the day was at the Clearville Member of the Mahantango Formation, which had lots of lovely coral fossils in it:
Dan put together a Google Map of our 17 stops; if you’re interested in checking out some of these places yourself, then this is a great resource.
I’d like to publicly thank Dan for taking a work day to contribute to our understanding. It was a lot of fun!