3 September 2014
Rugose corals in the Clearville member of the Mahantango Formation
Posted by Callan Bentley
Here are some rugose coral fossils (along with some cross-sectioned articulate brachiopod shells) to be seen in the Clearville member (~80 feet thick) of the Mahantango Formation, exposed on the north side of route 55, just west of the West Virginia / Virginia border.
These fossils are cool in their own right (what fossils aren’t?) but here they’re serving another purpose – they’re letting us know where we are in the stratigraphic stack. This is really useful when you’re out in the Valley & Ridge, and all the strata are folded and faulted and “reshuffled” in a way that makes it hard to keep track of where/when you are. They serve, in other words, as a marker horizon. I’m grateful to Dan Doctor (USGS) for cluing me into them.
Bob Gaines did his W&M senior thesis on this outcrop. There’s a poorly reported oolitic bed hiding there.
I saw that oolitic bed, actually. We inferred it was out of place, since it’s poorly reported, I guess. Here are images of it: https://blogs.agu.org/mountainbeltway/2014/04/30/ooh-ooh/