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6 October 2014
Non-bedding-parallel stylolites in Tonoloway limestones, Corridor H
What can a little squiggle in a rock tell us? Stylolites in West Virginian limestone cut across the bedding plane, implying Alleghanian tectonic stresses.
8 August 2014
Friday fold: Buckle vs. passive folding in the Chancellor Group slates
The Friday fold is an outcrop in Yoho National Park that showcases differences between buckle folding and passive folding.
6 May 2014
McKittrick Canyon, Guadalupe Mountains National Park, Texas
While in West Texas over spring break, the “Border to Beltway” students took a hike up McKittrick Canyon, in Guadalupe Mountains National Park. This is part of the famed Permian reef complex, the deep reservoir of Texas’s rich endowment of oil. Here, the reef comes to the surface. In fact, it pokes up a good bit into the air: Can you see it? If not, let Marcelo, Robin, and Nicole …
10 April 2014
Fusulinids and stylolites, Hueco Formation
My colleague Joshua Villalobos shared this image with me the other day – it’s a thin section of fusulinid-bearing limestone of the (Permian aged) Hueco Formation, from the Tom Mays Unit of Franklin Mountains State Park, Texas. Click to enlarge Note the scale bar at lower left. The big fusulinid in the middle is 3mm in diameter! And that’s not even it’s longest axis! Fusulinids were big honking burrito-shaped protists …
20 February 2014
Stylolite from the Helderberg Group, exposed on Corridor H
While out on the Corridor H field trip last week before the heavy snow, I found this squeal-inducingly-lovely example of a stylolite in Helderberg Group limestones (Devonian passive margin carbonates): The stylolite is a pressure-solution surface, made especially apparent in this example because of the starkly different grain sizes and colors on either side of the dissolved-away rock: This is a gorgeous sample to explore in macro GigaPan view. Enjoy: …
5 September 2013
Strained stylolites at Foamhenge
One thing that’s 100% worth doing if you find yourself visiting Natural Bridge, Virginia, is to pop in for a visit at Foamhenge, an art installation a few miles away. Foamhenge is a full-scale replica of Stonehenge, made of styrofoam (covered in gray latex paint). It’s a few years old now, so it’s begun to weather a bit: You’ll notice that classic orange soil and that there are also outcrops …
15 August 2013
Disconformity in northern Colorado
Have a look at this lovely (almost glowing) example of a disconformity between Coloradan limestone and overlying sandstone.
22 March 2013
Friday fold: the case of the strangely stout stylolites
Today, we return to my field trip from last week, for a look at an odd outcrop of the Ordovician-aged Edinburg Formation: Note the car key with green lanyard, to provide a sense of scale. It’s folded, as the yellow bedding traces show in this annotated version: But what really caught my eye about this outcrop were the odd stylolites (pressure solution “seams” with a wiggly morphology and a concentration …
21 February 2013
Strained stylolites in Elkton East
Whoa – look at all that GREEN. You can tell this Virginia picture wasn’t taken recently. In fact, it’s another image from the field review I participated in for the Elkton East quadrangle back in May of last year. Somehow I start blogging these things, but run out of steam (or really more accurately: I get distracted by other stuff) before I finish. Today’s (I think, final) tidbit: sheared stylolites …
8 August 2012
What those geologists were looking at
Yesterday, I showed you a scene of geologists (including me) clustered around some (presumably interesting) outcrop. I asked what you thought we might be looking at. Howard Allen, a denizen of this part of the globe, immediately identified the scene as that of the downstream end of the Athabasca Glacier. Several people guessed that we were looking at “glacial striations,” and that’s a good guess. Indeed there were plenty of …
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.