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26 October 2015
Tool marks, trace fossils, and flute casts from the Brallier Formation
Another gem from Saturday’s Historical Geology field trip: the bottom of a fine sandstone bed in the Devonian Brallier Formation, showing a variety of primary sedimentary structures, including tool marks, trace fossils, and several flute casts. Current flow direction here would have been from upper left toward lower right. Here’s a version of the photo with a few of these features highlighted:
25 October 2015
Cool fossils from the Clearville member of the Mahantango Formation
On Saturday, I took my historical geology class on their field trip out to Corridor H, West Virginia. We made a stop at the Mahantango Formation outcrop exposed on the eastbound exit ramp near Baker, and poked around there for fossils. These Devonian-aged siltstones are chock full of invertebrates including rugose corals, crinoids, articulate brachiopods, and even trilobites. Here are two of the best fossils we encountered there: A trilobite …
20 August 2015
Stromatoporoids in a Devonian reef
Here are a few shots of a Devonian aged reef exposed in Mustoe, Virginia – one of the sites I visited this spring with GMU’s Rick Diecchio, when he led his sedimentology and stratigraphy trip there. At first, the outcrop made no sense to me – I kept searching for bedding, and failed to find it. Then, the reef interpretation clicked, and suddenly I didn’t “need” bedding any more… Stromatoporoids …
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 …
8 May 2015
Friday fold: Foreknobs formation
Last one in the triumverate sent in by reader Eric Fulmer: Annotated: Happy Friday and (for many of you) happy end of the semester!!
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.
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 …
19 March 2015
Zoophycos trace fossils in Mahantango Formation, Fort Valley
A morning’s field trip yields an outcrop of excellent Zoophycos trace fossils in southern Fort Valley, Virginia.
24 November 2014
Non-bedding-parallel stylolites in Helderberg limestones, Corridor H
Saturday I posted some images of bedding-parallel stylolites from one member of the Devonian-aged Helderberg Formation (or one formation in the Helderberg Group; I’m not sure whose stratigraphy is preferable in this case). Here we are, further up-section, and you can see both bedding-parallel and non-bedding-parallel stylolites overprinting the limestone: Bedding-parallel stylolites can be understood readily in terms of sedimentary loading (compression from above), but non-bedding-parallel stylolites imply a maximum …
3 September 2014
Rugose corals in the Clearville member of the Mahantango Formation
Here are some rugose coral fossils (along with some cross-sectioned articulate brachiopod shells) to be seen in the Clearville member (~80 feet thick) of the Mahantango Formation, exposed on the north side of route 55, just west of the West Virginia / Virginia border. These fossils are cool in their own right (what fossils aren’t?) but here they’re serving another purpose – they’re letting us know where we are in …
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.