Cleaning out the backlog of photos I haven’t popped up here yet… Here’s three shots from last weekend, of folds (some kinky) which deform Harpers Formation foliation, just south of Harpers Ferry, West Virginia: The Harpers is a Cambrian-aged lagoonal mudrock, dated via Olenellus trilobites in Pennsylvania. It is part of a transgressive sequence that … Read more
The Lilster & I drove out to Harpers Ferry, West Virginia, today, and crossed the Potomac River to hike up to the overlook at “Maryland Heights,” which is what they call the Blue Ridge north of the river. On the way uphill, I noticed this nice example of Harpers Formation bedding and cleavage dipping in … Read more
Today, you get a photo from GMU structure student Nik D. This is a small exposure in the Hampshire Formation (Devonian) on New Route 55 in West Virginia. It shows a fine example of plumose structure with the not-often-seen concentric ribs running perpendicular to the ‘plumes.’ At the edge of the joint, you can see … Read more
I took a look at some interesting blobby structures in the Swift Run Formation last week, and walked readers through my logic in tentatively concluding that they were ball & pillow structures (soft sediment deformation), though overprinted by a pervasive (Alleghanian) cleavage. As we move west in the Appalachian mountain belt, the rocks are less … Read more
Remember the mud I saw on Pimmit Run? Turns out that West Virginia mud pulls many of the same tricks as Virginia mud. Here’s some mud cracks I noticed on Sunday afternoon on the shoulder of New Route 55 in eastern West Virginia: Notice how West Virginia spices her mudcracks with chunks of Silurian quartzite … Read more
Okay; we are nearing the end of our Transect saga. During the late Paleozoic, mountain building began anew, and deformed all the rocks we’ve mentioned so far. This final phase of Appalachian mountain-building is the Alleghanian Orogeny. It was caused by the collision of ancestral North America with the leading edge of Gondwana. At the … Read more
We just looked at the Chilhowee Group, a package of sediments that records the transition for the North American mid-Atlantic from Iapetan rifting through to passive margin sedimentation associated with the Sauk Sea transgression. Well, if we journey a bit further west, we see the sedimentary stack isn’t done telling its story. The saga continues … Read more
…So where were we? Ahh, yes: an orogeny, and then some rifting. What happened next to Virginia and West Virginia? Let’s consult the column… After the rifting event opened up the Iapetus Ocean, seafloor spreading took place and tacked fresh oceanic crust onto the margin of the ancestral North American continent. As North America (“Laurentia”) … Read more
Over on the far right by Chuck Bailey (yellow shirt) you can see the crescent-shaped profile of a river channel (gray color). To the left of that, you can see levee deposits, and beyond that (to the left) crevasse splay deposits and the floodplain (dark red mudstones). This is in the Hampshire Formation, part of … Read more
Here we are in the Brallier Formation, a Devonian turbidite sequence. Prominent in the middle of this photo is the Bouma “C” horizon with the cross- bedding.