Another sterling TR, including another tantalizing view of DV geology. If there is anywhere in the Lower 48 which has more varied and and well-exposed geology, I'd love to see it. I've GOT to get out there some time!
The brief read I did on the Kingston Peak Formation as a deposit of glacial sediments brings back fond memories of geology lessons past and recent. Reference is made to "dropstones" within the Kingston Peak Formation. Our petrology and sedimentation/stratigraphy professors delighted in taking students to outcrops of the Konnarock Formation at the foot of Mount Rogers, VA, not far from our home base at Appalachian State U, Boone, NC. The outcrops showed large clasts of all sorts of older rocks within a very fine mudstone matrix. The juxtaposition of the large clasts (normally indicative of a high energy depositional environment) and the mudstone (normally indicative of a low energy depositional environment) was puzzling to the newbie petrology and sed/strat students. It was rare that anybody "got it" without some leading questions provided by the professors.
Dropstones, you see, are deposited in large glacial lakes, where very fine-grained sediments fill the depths, minding their own business until a raft of ice calves off and floats out away from the high energy shoreline--a raft carrying chunks of gravel plucked from the floor and walls of the glacier's valley. As the raft of ice melts, its cargo sinks to the bottom, plunked into the soft muds below. Once hardened into rock, the rock's clasts are referred to as, you guessed it, dropstones.
The Konnarock Formation glacial deposits are of somewhat younger than the basement rocks of the Death Valley area, and were deposited in the late Precambrian, at which point in time the position of what is now southwestern Virginia was close to today's South Pole. That's a lot of continental drift, eh?
Foy
