I took my structural geology students to that fine outcrop of the Swift Run Formation in eastern Shenandoah National Park on Friday. There, we saw lovely primary structures with tectonic fabric overprinting (as I have showcased here previously). Consider this graded bed with subsequent (vertical) cleavage: And here’s the hinge of a nice passive fold, … Read more
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…
In December, Callan found an outcrop of Neoproterozoic-aged turbidites in South Africa, on the eastern shore of False Bay.
Hand sample of folded limestone strata in West Virginia (presumably Devonian in age). Note the rip-up clasts and large grain size at the base of the sample (to the right in the photo). Note the fine-grained, thin-bedded shale laminations towards the top (left) of the sample, too. Together, they tell a story of decreasing energy … Read more
After a roadside explanation just an hour and a half earlier on how the relationship between bedding and cleavage can reveal whether bedding is likely right-side-up or up-side-down, my students and I were walking up the road to the Ancient Bristlecone Pine Forest in the White Mountains of California, and I saw this outcrop that … Read more
Callan and his field studies students encounter a lesson in the White Mountains of eastern California that combines bedding, cleavage, folding, and even fossil archaeocyathids!
Incipient mylonitization of a granite/granitoid, as displayed in a sample on a shelf of one of the meeting rooms adjacent to the Reading Room of the Geological Sciences building at the University of Texas at El Paso. Same side, slightly different lighting conditions: I’d call this a protomylonite. Some of you might prefer the term … Read more
Today, two examples of outcrops that reveal an overprinting relationship between metamorphic cleavage and sedimentary bedding. Both are Devonian in depositional age, from the new stretch of New Route 55 in West Virginia, west of Moorefield. The first is from limestones of the Helderberg Group, and the second is from shale of the Brallier Formation. … Read more
Callan reviews the geology of the superlatively auriferous Witwatersrand Supergroup of South Africa, and then zooms in on a distinctive marker bed near the base of the sequence. The deformation in this particular banded iron formation (BIF) is an aesthetic wonder, as this suite of images reveal. The layer outcrops in the heart of urban Johannesburg.
This summer, a week or two after our wedding, my wife and I found ourselves in the Canadian Rockies for a pre-honeymoon. Part of our time was spent on a backpacking trip to Floe Lake in Kootenay National Park, British Columbia. On our hike in, we passed this outcrop of Chancellor Slate, a Cambrian aged … Read more