Today the Friday fold comes with copious bonus structures. It’s the first stop we hit on Day 3 of the pre-GSA Minneapolis field trip to examine the structural geology of the subprovince boundaries within the Superior Craton. This particular site showed granitoid dikes that had been deformed during dextral transpression into a variety of structures … Read more
Okay – in spite of numerous distractions (see every other post so far this week), it’s time to return to the pre-GSA Minneapolis structural geology field trip. Our final stop of the second day in the field was a series of folded up mafic metavolcanics. I’ve got some photographs of them. These mafic volcanics were … Read more
You may recall that I kind of like boudinage. So it piqued my interest when our field trip leaders (on the pre-GSA Minneapolis trip to examine the structural geology of the sub-province boundaries in the Superior Craton) said our next stop was to visit “pseudoboudins,” segments of granitoid pegmatites that looked like boudins but probably … Read more
Here’s the talk I gave at GSA last month: [youtube=”http://www.youtube.com/watch?v=oXt5aZIu5Xk”] It’s presented here at a slower pace than the actual talk was, since I didn’t have to run and catch a plane 45 minutes after presenting it, but there are some PowerPoint bugs with some of the animations. Oh well – recording it and … Read more
Picking up from the astonishing first couple of outcrops we saw of strained Seine Group metaconglomerate from the boundary between the Wabigoon and Quetico sub-provinces of the Superior Craton, our group moved on down the road. It was lovely clear fall weather near Fort Frances, and shockingly warm. Our third stop of the morning was … Read more
I’m on the plane home from the annual meeting of the Geological Society of America, held this year in Minneapolis, Minnesota. This annual event features a robust smorgasbord of science, with talks and posters detailing the research efforts of thousands of geoscientists from the US and other countries. It’s an amazing experience on many, many … Read more
Picking up where we left off last time, we were in some partly-serpentenized peridotite, part of the Burham Ophiolite in Turkey’s Tavşanlı Zone, an ancient tectonic suture. Our next stop on the field trip allowed us to visit some diabase dikes: Here’s a close-up of the right contact of the dike with the host peridotite: … 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
It is time to debrief the post-NE/SE-GSA field trip that I went on, affectionately dubbed the “Transect Trip” for the past 27 iPhone-uploaded “live”-geoblogged posts. First off, I’d have to say that I enjoyed the live-field-blogging experiment overall, though I’ve got some critiques of the process and products. I think it’s amazing that I can … 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.
This one is also from the Millboro Formation: itty bitty brachs (not too much oxygen in those depths for building up big body sizes) that have been sheared during Alleghanian deformation.
This photo is from the Millboro Formation: mostly deep water black shale, but with the occasional heavy turbidite coursing in and settling its bulk down on the squishy mud beneath. Some folks on our trip suggested these might be seismites: soft sediment deformation resulting from earthquake-induced vibration.
Nice set of twist hackles on the fringe of this joint face:
Oriskany sandstone, folded into an S-fold, then snapped down the middle!
Hoo-hoo! An anticline in the hanging wall of a thrust fault in the Valley & Ridge. This is the redbeds of the latest-Ordovician Juniata Formation. Lynn Fichter for scale.
This is a nice sample of slicks. On the other side, burrows! I like that: a primary structure on one face, a secondary structure on the opposite side.
Looking north along the Germany Valley, which lies in the core of a breached plunging anticline. The topography is defined by the erosion-resistant ridge of Tuscarora Sandstone. This is the Wills Mountain Anticline. The Tuscarora is Silurian; at the bottom of the valley (core of the anticline), you find Ordovician carbonates.
Fault-duplicated double section of the (Silurian aged) erosion-resistant Tuscarora Sandstone:
Sweet hackles on the right; pen for scale.