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18 October 2017
VGFC 2017: Limbs of arkose
The 2017 Virginia Geological Field Conference had a heavy arkose infusion. Meet some of these feldspar-rich Neoproterozoic sediments of the Lynchburg Group.
29 September 2017
Friday folds: soft sediment deformation in thin sections of MTD sandstone
The Friday folds are small soft-sediment deformational features within a dismembered, folded sandstone (a “ploudin”) from a mass transport deposit from the latest Devonian of West Virginia.
6 June 2017
Loading sags in homogeneous lithologies?
Can soft sediment deformation “loading structures” (ball & pillow) occur when the two strata are identical in composition? Grok on these field photos and chime in with your best hypothesis.
5 June 2017
3D models of sedimentary structures
I’ve been busy making 3D models lately. Here are three ones united by a theme of being sand that was deposited relative to mud. In one case we have scouring to make flutes, in another case we have have localized sagging to make “ball & pillow” structures, and in the third case we have an extraordinary submarine landslide deposit. For two of them, the shale has been preferentially etched away, …
1 June 2017
The geology of the Yesnaby coast, Orkney
Ahhhh, a raw Scottish coast. …Let’s go there. There’s sedimentology to be learned here, and coastal geomorphology to be ogled. This is Yesnaby, on the west side of Orkney. The rocks there are part of “the Old Red Sandstone,” a neat package of Devonian strata, flavored here and there with an igneous dike, a fault, etc. But overall, I’d like to focus on the strata. The strata I saw at …
25 May 2017
Chert-slab conglomerate from the Fig Tree Group, Barberton
Deep in the Archean, things suddenly got violent in the deep water of the Mapepe Formation’s oceanic setting. What was a quiet precipitation of chert suddenly was torn apart and tumbled downslope. Was an earthquake to blame? A bolide impact? This is the result.
9 May 2017
Ripples in Foreknobs
The Foreknobs Formation is a Devonian unit in the Valley & Ridge province of the Mid-Atlantic Region. It was deposited in relatively shallow near-shore conditions during the Acadian Orogeny. On a field trip to Corridor H, a new highway transecting the West Virginian Valley & Ridge province on Monday, I stopped to document a couple of beds showing very nice ripple marks. These ones are symmetrical, and thus likely represent …
3 May 2017
Storm beaches have I loved
The answer to yesterday’s geo-puzzle is revealed to be a storm deposit of boulders, 20 m above sea level!
28 March 2017
P-sol in a conglomerate countertop slab
A hardware parking lot in rural Virginia showcases an elegant slab of pressure-solution induced compaction of a conglomerate.
9 March 2017
Lugworm casts on the beach, Islay
Who dwells beneath the sands of Islay? Lugworms do. These embedded annelids process the sediment for food, extruding the undigested sand in charismatic piles that adorn the beach of Loch Gruinart.
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.