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11 April 2012
Blue Ridge Thrust Fault field trip
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…
30 January 2012
Brallier cross-beds
More evidence of currents in the Devonian deep… Primary structures that give us clues, preserved in a place where preservation over 360 million years isn’t necessarily guaranteed. As you might expect, this turbidity currents roared in from the east, where the mountains were rising, and generating a fair bit of sand and mud, during the Acadian Orogeny. (The view in this photo is looking towards the south.)
27 January 2012
Friday fold: Twisted turbidites
These are turbidites of the Malmsbury Group in South Africa, on the east shore of False Bay. A couple of nice little folds running sub-vertically through the package… Happy Friday!
17 November 2011
Shear zone in basement complex
Callan visits a new outcrop of highly-sheared rocks in the basement complex of Virginia’s Blue Ridge province.
1 March 2011
News from the Billy Goat Trail (3): grab bag
Okay, a final post (for now, anyhow) sharing some images from last Friday’s field trip to the Billy Goat Trail, in Potomac, Maryland. Yesterday we looked at lamprophyre dikes, but there are other dikes on the Billy Goat Trail, too. Like this granite pegmatite: What’s interesting to me about this is that the joint set seems to have contradictory cross-cutting relations with the dike. Did the joints come first? Or …
28 February 2011
News from the Billy Goat Trail (2): lamprophyre dikes
Lamprophyre dikes on the Billy Goat Trail (Potomac, Maryland): are they offset because of a fault? Or not? Inquiring minds want to know!
27 February 2011
News from the Billy Goat Trail (1): Graded beds
I took my structural geology students out the Billy Goat Trail (upstream half of the “A” loop, near Potomac, Maryland) last Friday, and had them gather data for a project to assess whether or not Mather Gorge is controlled by a fault. I got this idea from Aaron Martin, the structural geologist at the University of Maryland, and I think it’s a nice project for structure students early on in …
24 December 2010
Friday fold: Mars Hill terrane
Today’s Friday Fold comes to us via Pete Berquist of Thomas Nelson Community College in Hampton, Virginia. Check it out: Pete explains what’s going on here: I cannot provide an exact location but this is within the Mars Hill Terrane (MHT), which is an distinctive swath of Mesoproterzoic basement extending ~50 km x 100 km within the North Carolina Blue Ridge. It may be analogous with the Stage Road Gneiss …
22 August 2010
Geology of Massanutten Mountain, Virginia
Here’s a new video from Greg Willis, the same guy who brought us a fine video on Piedmont geology. In this new opus (20 minutes), Greg details the geology of the Massanutten Synclinorium (Shenandoah Valley, Massanutten Mountain, and Fort Valley) in western Virginia. WordPress isn’t letting me embed it here, but you should go and check it out!
30 March 2010
Sugarloaf
Sunday morning, NOVA adjunct geology instructor Chris Khourey and I went out to Sugarloaf Mountain, near Comus, Maryland, to poke around and assess the geology. Sugarloaf is so named because it’s “held up” by erosion-resistant quartzite. It’s often dubbed “the only mountain in the Piedmont,” which refers to the Piedmont physiographic province. Here’s a map, made with GeoMapApp and annotated by me, showing the general area: A larger version of …
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.