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5 April 2013
Two new GigaPans of Rockfish Gap, Virginia
I took a trip down to Charlottesville this week for a couple of meetings, and I made time along the way to capture two new GigaPans of the lovely exposures of Catoctin Formation greenstone at Rockfish Gap, where Interstate 64 traverses the Blue Ridge. This is very close to the southernmost tip of Shenandoah National Park, and at the northern terminus of the Blue Ridge Parkway. The Catoctin is an …
25 March 2013
Incipient boudinage in overturned Edinburg Formation
Boudinage is such a fun structure. Here’s an example from the roadcut adjacent to the quarry featured so heavily last week. The thick limestone stratum in the center of the photo has been stretched left-to-right. It exhibits pinch-and-swell structure, the first stage of boudinage. Small extensional fractures began to form in the boudin necks, accommodating the strain. Muddier strata above and below flowed into these boudin necks. This is in …
3 January 2013
Inside the French Thrust
Callan zooms in on the meso-scale structure of the French Thrust fault, exposed in Sun River Canyon, Montana.
7 September 2012
Friday folds: Selkirk Fan
The Friday fold is a selection of five fold photos from the Selkirk Fan in the Omineca Belt of British Columbia, submitted by structural geologist Marek Chichanski of De Anza College (California).
31 July 2012
Deformed carbonatite dikes in Cambrian slate, Yoho National Park, British Columbia
Callan’s Canadian Rockies field course visits an outcrop of Cambrian slate in Yoho National Park, British Columbia. Folded and boudinaged carbonatite dikes are seen.
3 July 2012
Granite dikes that have been folded and boudinaged
It seems like a good morning to return to Ontario, and to the Archean shear zones exposed at the Quetico/Wabigoon subprovince boundary of the Superior Craton. Readers will hopefully recall that I spent several days absorbing structural goodness from these rocks on a field trip before the Minneapolis GSA meeting last fall. The trip was led by Basil Tikoff, Bob Bauer, Dyanna Czeck, and Peter Hudleston. Our final Canadian stop …
30 April 2012
Exquisite boudinage in Ontario
Callan shares images of extraordinary boudinage outcrops in strained Archean meta-basalts on the Quetico-Wabigoon subprovince boundary within the southern Superior Craton. Ogle these gorgeous structures in awe and wonder.
21 March 2012
More folds from the White Mountains
I know we spent time last Friday on some nice folds in the Poleta (?) Formation in the White Mountains of California, but here are a few more that I saw on my way up to the Ancient Bristlecone Pine Forest… Some elliptical objects caught my eye: Traced out along the plane of bedding, these turned out to be boudins of a more competent layer, which was tightly folded higher …
13 December 2011
Dikes crossing dikes
A pretty cool outcrop I saw on my pre-GSA structural geology field trip to the Superior Craton: Can you see what caught my eye here? It’s a nice series of cross-cutting relationships. A series of sedimentary rocks were sheared out and metamorphosed, transforming into schists with internal boudins, and then they were cross-cut by first a felsic dike, and then a mafic dike, as seen in this modified version of …
2 December 2011
Friday folds (and boudinage): Superior Craton day 3, stop 1
Today the Friday fold comes with copious bonus structures. It’s the first stop we hit on Day 3 of the pre-GSA Minneapolis field trip to examine the structural geology of the subprovince boundaries within the Superior Craton. This particular site showed granitoid dikes that had been deformed during dextral transpression into a variety of structures depending on their initial orientation, pre-deformation. Those with orientations parallel to the maximum extension direction …
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.