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29 August 2015
Mystery structure: please help identify / interpret
I have a mystery for you today: These are samples of Tonoloway Formation carbonate (not sure if it’s limestone or dolostone in retrospect), with bedding more or less horizontal in these images, and a few petite stylolites running orthogonal to that. The top sample has a gentle fold 2/5ths of the way across. All of the samples are from the same site in West Virginia, along Corridor H. I’m wondering …
21 August 2015
Friday fold: a kink fold at Baldwin Gap
Ladies and gentlemen, I give you… The Friday fold: This beauty came to my attention on Monday, when I was lucky enough to go on a field trip with my friends Leigh and Mary. They are founding members of our local informal geology club, and we have been meaning to take a Cedar Creek field trip together since I moved out to the Fort Valley. One of the sites we …
28 July 2015
Millboro Formation shale in outcrop and in hand sample
Another site from the GMU sedimentology field trip in April: An outcrop on Route 33 in Brandywine, West Virginia, showing the Millboro Formation. It’s mostly shale, with some intriguing sandstones, too. There are fossils and diagenetic carbonate nodules (concretions). Here’s the outcrop, the largest GigaPan I’ve taken so far (7.9 billion pixels): link The shale itself looks… like shale. It’s fine-grained, and dark (high carbon content, suggesting low oxygen levels …
1 May 2015
Friday fold: Tight syncline/anticline pair in Brallier Formation
The Friday fold shows clastic detritus (turbidites or “flysch” from the Acadian Orogeny) crumpled into tight folds due to the later Alleghanian Orogeny.
30 April 2015
Early Paleozoic fossils in Nealmont Formation, Germany Valley, West Virginia
Looking at Ordovician carbonates in Germany Valley, West Virginia, a few weeks ago on Rick Diecchio’s GMU sedimentology and stratigraphy course field trip: Lots and lots of brachiopods… Crinoid columnals mized with brachiopods: A set of coarsely-infilled trace fossils: Crinoid stem: Nice strophomenid brachiopod: Bryozoan? Receptaculid?
24 April 2015
Friday fold: Bloomsburg Formation at lime kilns on C&O Canal
Milepost 127.4 (High, 2001) on the C&O Canal: …Cool if you’re into history. …Cool if you’re into economic geology. …Cool if you’re into Friday folds! Reader Eric Fulmer sent me this photo (along w/ two others you’ll see in weeks to come). Thanks, Eric!
15 April 2015
Spring time
This past weekend, I had a chance to visit Bath, Highland, and Alleghany Counties, Virginia, three amazingly beautiful places I had never before seen. I was tagging along on my colleague Rick Diecchio’s annual sedimentology & stratigraphy field trip for George Mason University. I was eager to learn from some awesome field sites from him in the year before he retires. We saw some terrific sedimentary rocks, of which more …
6 April 2015
Exploring Mahantango Zoophycos traces in GigaPan
Recently, I posted about an excellent road cut in Fort Valley showing well-developed 10 cm+ Zoophycos trace fossils. Presented here are three new GigaPan images (two outcrop; one macro) of Zoophycos from the Devonian-aged Mahantango Formation: link link link These images are part of a new “virtual field trip” that I organized to supplement my historical geology field trip to examine the geologic history of the Massanutten Synclinorium. The link …
24 March 2015
Martinsburg Formation outcrops in Edinburg Gap
A report from the field: new outcrops of Ordovician-aged turbidites featuring geopetal indicators, fossil content, and a structural overprint imparted during Pangaea’s assembly.
20 March 2015
Friday fold: flexed turbidites
Spring is almost here! As you get ready for the equinox, enjoy this gentle fold on a Friday: These are turbidites (graywacke and shale) of the late Ordovician Martinsburg Formation, seen in Edinburg Gap, western Massanutten Range, greater Shenandoah Valley, Virginia. Bedding is flexed very slightly here, from moderately-dipping to more steep, and then back to moderate again. Slickensides on the top of some exposed layers indicate the beds shifted …
Callan Bentley is Associate Professor of Geology at Piedmont Virginia Community College in Charlottesville, Virginia. He is a Fellow of the Geological Society of America. For his work on this blog, the National Association of Geoscience Teachers recognized him with the James Shea Award. He has also won the Outstanding Faculty Award from the State Council on Higher Education in Virginia, and the Biggs Award for Excellence in Geoscience Teaching from the Geoscience Education Division of the Geological Society of America. In previous years, Callan served as a contributing editor at EARTH magazine, President of the Geological Society of Washington and President the Geo2YC division of NAGT.