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7 May 2021
Friday fold: Lynchburg Group
On his way to get his COVID vaccine, Callan visits a new outcrop showing folded and faulted strata of the Neoproterozoic Lynchburg Group.
31 July 2020
Friday fold: Two Mile Run Overlook
I spied an anticline last weekend while engaging in a day of solo geologizing along Skyline Drive in Shenandoah National Park. At Two Mile Run Overlook, I gazed west toward the southern tip of Massanutten Mountain, and noted what appeared to be an anticline in the Blue Ridge foothills: Annotated: And here it is in Google Maps, with the perspective rotated to looking ~along strike to the north, and I …
14 June 2019
Friday fold: kinked cleavage at Harpers Ferry
Last weekend was the annual meeting of the eastern section of the National Association of Geoscience Teachers. On Friday afternoon, we visited Harpers Ferry, West Virginia, and my colleague Beth Doyle led a great field trip to examine the rocks exposed there. This was my favorite outcrop we saw: Here is a close up of this outcrop, which is framed by (anthropogenic) rock wall: Dipping shallowly from upper left to …
13 April 2018
Friday fold: Blue Ridge gneiss in the University of Kentucky rock garden
The Friday fold is on display in a rock garden outside the Department of Earth and Environmental Sciences at the University of Kentucky.
30 March 2018
Friday fold: Recumbent Harpers
Stop the presses! This late-breaking Friday fold has just been submitted here at Friday Fold Headquarters. This is from Philip Prince/Virginia Division of Geology and Mineral Resources: It’s a recumbent fold of Harpers Formation metasandstone in the James River Face area. Pretty lovely exposure. This outcrop would make a good 3D model. Happy Friday to all. Hope it’s a good one!
19 January 2018
Friday fold: crumpled quartz vein from VGFC
Remember the Virginia Geological Field Conference from back in October? Well here’s a folded quartz vein we observed along a small shear zone in the Blue Ridge basement complex. There are two views of it, from approximately perpendicular points of view: These rocks are Mesoproterozoic, but the vein would obviously be younger than that, and the deformation is likely Alleghanian in age (late Paleozoic). Annotated copies of the photos:
27 October 2017
Friday fold: Quantankerous veins
What does it mean for a vein to be “quantankerous?” Well, to start with, it’s quartz. Second, it has to be disagreeable or cantankerous. This vein, seen in meta-arkose of the Catoctin Formation near the summit of the Blue Ridge at Rockfish Gap (not Afton Mountain), is such a quantankerous individual: You’ll notice its “S” shape, which might imply top-to-the-left kinematics. But just down the outcrop is this set of …
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.
15 April 2017
Basement xenoliths in Catoctin Formation, Compton Pass
My son and I hiked Compton Peak in Shenandoah National Park this morning, and saw these two lovely examples of xenoliths. The example above is small, but it shows clearly the difference between the coarse, felsic basement rock (Mesoproterozoic granitoid, comprising the xenolith) and the surrounding fine-grained dark green metabasalt of the Catoctin Formation (Neoproterozoic). Here’s another, bigger example: These two Blue Ridge examples both illustrate the principle of relative …
6 June 2016
Cleavage refraction in Konnarock Fm. rhythmites – a virtual sample
Here’s a visualization combination that leverages the advantages of the GIGAmacro system with the 3D ‘virtual sample’ perspective of the Sketchfab-hosted model: the same sample presented in both formats. In this case, it’s a lovely example of cleavage refraction going from meta-clay-shale (now ‘slate’) through a graded bed of fine sand and silt. Link GIGAmacro by Callan Bentley Photoscan model by Marissa Dudek The sample is of the Neoproterozoic Konnarock …
Callan Bentley teaches 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.