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12 June 2023
I spent yesterday on Corridor H in eastern West Virginia’s Valley & Ridge province. The rocks here are a mid- to upper-Paleozoic set of strata that record the switch from post-Taconian passive margin sedimentation into Acadian clastic deposition, and then everything is deformed by Alleghanian folding and thrusting. I found myself taking photographs of the same old outcrops I know and love there – but here’s something new that I …
18 April 2018
The Cretaceous-Paleogene limestone called Scaglia Rossa was used to construct a basilica in tribute to St. Francis. Let’s head to Assisi and take a look.
9 June 2016
Our series of virtual samples continues! This week, I’m presenting examples of 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. Today, we feature a lovely slab of limestone, chock full of fossil material, and showing both primary sedimentary structures like graded bedding and cavity fills (both geopetal indicators), but also …
19 November 2015
What geological stories can be read from the stone on the front of a building? Walking past some facing stone in Baltimore, Callan discovers a wealth of little clues.
29 August 2015
I have a mystery for you today: These are samples of Tonoloway Formation carbonate (not sure if it’s limestone or dolostone in retrospect), with bedding more or less horizontal in these images, and a few petite stylolites running orthogonal to that. The top sample has a gentle fold 2/5ths of the way across. All of the samples are from the same site in West Virginia, along Corridor H. I’m wondering …
22 December 2014
Want to see something cool? Itty bitty stromatolites… like baby’s fingers! There’s a big weathered-out stylolite at the base of this stromatolite-bearing layer, too. These elfin stromatolites are part of the boulder in the lower left (foreground) of this GigaPan, taken at the Icefields Center parking area in Jasper National Park, Alberta: link
24 November 2014
Saturday I posted some images of bedding-parallel stylolites from one member of the Devonian-aged Helderberg Formation (or one formation in the Helderberg Group; I’m not sure whose stratigraphy is preferable in this case). Here we are, further up-section, and you can see both bedding-parallel and non-bedding-parallel stylolites overprinting the limestone: Bedding-parallel stylolites can be understood readily in terms of sedimentary loading (compression from above), but non-bedding-parallel stylolites imply a maximum …
22 November 2014
Long week, no blog. But, hey – it’s Saturday, and I have a couple of hours of breathing room – so here are some stylolites in a crinoidal grainstrone in the New Creek member of the Helderberg Formation, exposed on Corridor H in West Virginia. Stylolites are pressure solution features, which overall form perpendicular to the maximum squeezing direction (maximum principal stress direction, σ1), and have little wiggle peaks that …
29 October 2014
I saw this large, chunky stylolite this summer somewhere along the trail from Takkakaw Falls to the Walcott Quarry of the Burgess Shale (in Yoho National Park, British Columbia). I like the way weathering has highlighted its form.
24 October 2014
Remember our examination of buckle folding versus passive folding in the Chancellor Slate (cleaved limy mudrock) of eastern British Columbia? Well, here’s another example: There’s so much awesomeness going on in that image, it’s hard to know where to start. The prominent black thin layers are buckled in a very boxy, asymmetric way. In places, the layer is discontinuous, suggesting faulting or shortening via pressure solution. Note how the cleavage …