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18 August 2022
Earlier this summer, I was lucky enough to visit a soapstone quarrying operation in Schuyler, Virginia, right on the Albemarle/Nelson County line. These soapstone bodies are metamorphosed ultramafic intrusions into the Neoproterozoic sedimentary deposits of the Lynchburg Group. The protolith peridotite sill crystallized at ~580 Ma, meaning the host sediments are older than that (but younger than the Grenvillian basement complex that underlies both). Then both plutonic rock and sedimentary …
24 June 2022
Happy Friday! Here are some kink-folded metasediments from Virginia’s Lynchburg Group to help usher in the weekend.
21 June 2022
One of my favorite tricks is using bedding / cleavage intersections to identify tectonically inverted strata. On a field trip yesterday to check out soapstone quarries in the Albemarle/Nelson border region, I got to see this lovely example of Lynchburg Group metasediments that showcased a textbook example of the phenomenon: Bedding was initially horizontal, or close to it, and cleavage (formed under tectonic compression) initially vertical. Subsequent deformation rotated the …
25 June 2021
Inside the Blue Ridge (in an 1850s-era railroad tunnel), Callan finds folds and boudinage that formed during Appalachian mountain-building.
7 May 2021
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
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
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
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
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
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
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
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
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
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. [gigapan id=”187755″] Link GIGAmacro by Callan Bentley [sketchfab id=”fb3eb77f46524d15b3a23649c63cd863″ start=”0″ spin=”” controls=”0″] Photoscan model by Marissa Dudek …
20 April 2016
An inaugural visit to an outcrop in Shenandoah National Park reveals the signature of lava flows ~600 million years old.
2 April 2016
Here are a few new images I’ve been working on with my home-based Magnify2 imaging system from GIGAmacro. Strophomenid brachiopods from Mississippian Mauch Chunk Formation, West Virginia: [gigapan id=”185738″] Link Boninite from New Caledonia: [gigapan id=”185707″] Link Lepidodendron scale-tree bark from Poland: [gigapan id=”185689″] Link Potassium feldspar crystal, from a pegmatite: [gigapan id=”185688″] Link Catoctin Formation greenstone from a feeder dike east of Linden, Virginia: [gigapan id=”185681″] Link Enjoy exploring …
31 March 2016
Anorthosite with lovely garnet reaction rims, a spherical hematite concretion, and some sweet breccia. Check them out and explore! [sketchfab id=”4453575da99743679a083363a0429b63″ start=”0″ spin=”” controls=”0″] [sketchfab id=”4333df612167415a8e216cef25e8cac6″ start=”0″ spin=”” controls=”0″] [sketchfab id=”cb58f446782d4736b699127884b46d16″ start=”0″ spin=”” controls=”0″]
29 March 2016
Here are a few new images I’ve been working on with my home-based Magnify2 imaging system from GIGAmacro. Archean basement complex gneiss from the Gallatin Range of Montana: [gigapan id=”185543″] Link (If this looks familiar, that’s because one of the samples I imaged with the Photoscan 3D modeling technique and published on Sketchfab the week before last.) Banded iron formation from Minnesota with ooids and stromatolites: [gigapan id=”185076″] Link Intrusion …
15 January 2016
The geology east of Harpers Ferry, West Virginia, is cool. It’s Blue Ridge rocks, from basement to the cover sequence, tilted to the west and broken and repeated by the Short Hill Fault. Here’s a look at a detail of the Geology of the Harpers Ferry quadrangle by Southworth and Brezinski (1996). So there’s a fault! Good – but the title of this post isn’t “Friday fault” – Where’s the …
12 October 2015
I’ve been thinking lately about Harpers Ferry, the spot where West Virginia, Virginia, and Maryland meet, at the confluence of the Potomac River and the Shenandoah River. I’ve noted small outcrops of its overturned beddding here previously, and also described a book I read about the man who made the place infamous: John Brown. I went out there again last week with my NOVA colleague Beth Doyle, and we explored …