One of Callan’s former students leads a field trip to examine the western edge of the Blue Ridge geologic province, attempting to answer the question of whether the Blue Ridge / Valley & Ridge contact is indeed the trace of a thrust fault. Breccias and S-C fabrics tell part of the story…
More evidence of currents in the Devonian deep… Primary structures that give us clues, preserved in a place where preservation over 360 million years isn’t necessarily guaranteed. As you might expect, this turbidity currents roared in from the east, where the mountains were rising, and generating a fair bit of sand and mud, during the … Read more
These are turbidites of the Malmsbury Group in South Africa, on the east shore of False Bay. A couple of nice little folds running sub-vertically through the package… Happy Friday!
Callan visits a new outcrop of highly-sheared rocks in the basement complex of Virginia’s Blue Ridge province.
Okay, a final post (for now, anyhow) sharing some images from last Friday’s field trip to the Billy Goat Trail, in Potomac, Maryland. Yesterday we looked at lamprophyre dikes, but there are other dikes on the Billy Goat Trail, too. Like this granite pegmatite: What’s interesting to me about this is that the joint set … Read more
Lamprophyre dikes on the Billy Goat Trail (Potomac, Maryland): are they offset because of a fault? Or not? Inquiring minds want to know!
I took my structural geology students out the Billy Goat Trail (upstream half of the “A” loop, near Potomac, Maryland) last Friday, and had them gather data for a project to assess whether or not Mather Gorge is controlled by a fault. I got this idea from Aaron Martin, the structural geologist at the University … Read more
Today’s Friday Fold comes to us via Pete Berquist of Thomas Nelson Community College in Hampton, Virginia. Check it out: Pete explains what’s going on here: I cannot provide an exact location but this is within the Mars Hill Terrane (MHT), which is an distinctive swath of Mesoproterzoic basement extending ~50 km x 100 km … Read more
Here’s a new video from Greg Willis, the same guy who brought us a fine video on Piedmont geology. In this new opus (20 minutes), Greg details the geology of the Massanutten Synclinorium (Shenandoah Valley, Massanutten Mountain, and Fort Valley) in western Virginia. WordPress isn’t letting me embed it here, but you should go and … Read more
Sunday morning, NOVA adjunct geology instructor Chris Khourey and I went out to Sugarloaf Mountain, near Comus, Maryland, to poke around and assess the geology. Sugarloaf is so named because it’s “held up” by erosion-resistant quartzite. It’s often dubbed “the only mountain in the Piedmont,” which refers to the Piedmont physiographic province. Here’s a map, … 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
New York City has some cool geology: Paleozoic metamorphics scraped by Pleistocene glaciers.
S.E. Central Park:
One of the cool things about being the local geoblogger is that people get in touch with you about local geology. Sometimes this even leads to meeting up for field trips. Here’s two quick photos from a recent (January 2010) field trip to a creek near Springfield, Virginia. My host was Barbara X, a local … Read more
A few photos from last May’s spring field trip with the Geological Society of Washington… Here’s the group at Chain Bridge Flats (far westernmost-Washington, D.C.), looked at the metamorphic rocks there — a metagraywacke melange known as the Sykesville Formation. Another group shot, with field trip leaders Tony (khaki shirt) and Gary (red jacket) Fleming … Read more