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7 May 2013
Brallier Formation 2: tectonic structures
Yesterday we examined primary sedimentary structures (including trace fossils) at an outcrop of Devonian-aged Brallier Formation turbidites between Deerfield and West Augusta, Virginia. Today, we’ll zoom in on the tectonic structures at the site: folds, faults, and joints. Remember, you don’t have to take my word for it. You can explore it for yourself in this M.A.G.I.C. GigaPan: link One thing that’s kind of cool about that GigaPan is the …
29 March 2013
Friday fold: “V”
The Friday fold photo was taken this morning on a GigaPanning expedition, and shows a small syncline within turbidite strata of the Martinsburg Formation, Page Valley, Virginia.
21 March 2013
Slicks in Cub Sandstone
During Alleghanian deformation (late Paleozoic), the Cub Sandstone we looked at yesterday was tilted to near vertical at Catherine Furnace. The shale layers developed cleavage at this time, and there was evidently some flexural slip between sandstone layers, to judge from these fine slickensides: Students: Can you deduce the sense of motion from the orientation of the structures in this sample? (Hint: note the directions the “steps” face…)
21 November 2012
Rock Cycle I: Sedimentary → Metamorphic
An outcrop of the Ordovician-aged Martinsburg Formation is used to illustrate the development of slaty cleavage, and hence a major transition in the Rock Cycle.
6 June 2012
Virginia geology on video: the Alleghanian Orogeny
Here’s another video, wherein I’ve made some improvements from the last one (reserved the lower right corner for the webcam “talking head” video inset, and adjusted the microphone for fewer audio blowouts). It’s still not perfect – there’s a disconnect between the audio and the webcam video that becomes more and more pronounced throughout the course of the video, but it’s a step in the right direction. The Alleghanian Orogeny: …
9 May 2012
Overturned bedding in the Weverton (?) Formation
On Monday, I was out in the field at the Blue Ridge / Valley & Ridge transition (“boundary”?) in the Elkton East quadrangle, where Chuck Bailey and students (from the College of William & Mary) were leading a field review of their new geologic map. A field review is a form of field-based peer review, wherein the authors of a new geologic map take peers and interested others out into …
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…
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.
20 September 2011
Giant City State Park, Illinois
Giant City State Park is a patch of protected forest south of Carbondale, Illinois, where there are some pretty cool exposures of Pennsylvanian-aged Makanda Sandstone. Here’s a typical look at one: Notice the deep chasm on the right. This leads, maze-like, to other flat-bottomed and vertically-walled canyons: The orthogonal joint sets produces some nice tall, cliff-like vertical exposures that reveal the history of these rocks in several stages: deposition by …
9 September 2011
Friday fold: just Kidding
You’re looking here at Mount Kidd, a peak in the Front Ranges of the Canadian Rockies that displays a tight anticline/syncline duo superimposed on the strata of the Rundle Group. Located on the west side of Highway 40, the Kananaskis Trail, south of the trans-Canada Highway, this mountain shows us what happens with Carboniferous-aged carbonates got squished and squeezed during the construction of the Canadian Rockies (what in the U.S. …
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.