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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 …
19 August 2015
Iron oxide sweat stains in sandstone
What do a sweaty baseball cap and fractured sandstone have in common? Episodes of absorption of dirty liquids that pile up material such as iron oxide at the soaking front.
14 August 2015
Paleoslump features and fluvial incision in the Conemaugh Group, West Virginia
The answer to this week’s geological interpretation contest is revealed, sort of. Annotations, GigaPans, and outcrop detail photos reveal the story of equatorial fluvial incision and ancient slumping during the Carboniferous ice ages.
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 …
20 May 2015
Liesegang banding in Pennsylvanian sandstones, Bolt Mountain, West Virginia
While out at the eastern section of NAGT’s annual meeting last weekend in West Virginia, I participated in a field trip to look at the stratigraphy of the Bolt Mountain section of Pottsville Group strata. One thing that was particularly eye-catching about the sandstones we saw was that many of them had been stained by rusty groundwater, producing the lovely stripey pattern known as Liesegang banding. Here are five examples: …
18 May 2015
Spheroidal weathering in sandstone
Here’s a nice example of spheroidal weathering in a sandstone, developed using orthogonal jointing and bedding: This is one of many sites I visited Saturday near Bolt, West Virginia, on a field trip with NAGT’s Eastern Section.
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 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 …
22 November 2014
Stylolites in Helderberg crinoidal grainstones, Corridor H
Long week, no blog. But, hey – it’s Saturday, and I have a couple of hours of breathing room – so here are some stylolites in a crinoidal grainstrone in the New Creek member of the Helderberg Formation, exposed on Corridor H in West Virginia. Stylolites are pressure solution features, which overall form perpendicular to the maximum squeezing direction (maximum principal stress direction, σ1), and have little wiggle peaks that …
14 November 2014
Friday fold: GSW fall field trip
Last Saturday was the Geological Society of Washington’s fall field trip. Dan Doctor, Alan Pitts, and I led a team of ~20 geologists out to the great new exposures along Corridor H in West Virginia. Here’s the team in front of some of the parasitic anticlines and synclines that decorate the larger structure of the Patterson Creek Mountain Anticline: The strata here are Silurian-aged tidal flat carbonates of the Tonoloway …
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.