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14 September 2018
Friday fold: Ferruginous sediments in Barberton Mountain Land
A trip back to Archean sedimentary rocks in Barberton, South Africa, reveals a few folds on the roadside…
7 September 2018
Friday folds: Continuing contorted Conestoga carbonates
The first Friday of September calls out for a fold. The Burle Business Park in Lancaster, Pennsylvania has an answer – several of them, in fact!
27 July 2018
Friday fold: new folds from the Empire Formation, Glacier National Park
Hiking Siyeh Pass in Glacier in Glacier National Park on Tuesday with my Montana State University field course, we spotted a few new folds in the Empire Formation (a transitional unit between Helena Formation and Grinnell Formation). Here is one of the students serving as a sense of scale, with interesting features on either side of him: On the left, there are small scale folds in a regular little train: …
6 July 2018
Friday fold: twisted turbidites at Usal Beach
Last week, I spent two perfect days camping with family at Usal Beach, in Mendocino County, California. Along the beachside cliffs there, I spotted plenty of lovely turbidites: graywacke and shale and a little bit of conglomerate that had been scraped off the subducted Farrallon Plate to help contribute to the bulk of the Franciscan complex. That accretionary process imparted some stresses on these deep-sea deposits, and in many places …
23 June 2018
Deformed conglomerate of Frog Lakes, California
Fifteen years after mapping deformed rocks of the Sierra Crest shear zone system in the high Sierra, a family vacation brings Callan back to the pre-batholith metasedimentary rocks which show a pronounced strain.
1 June 2018
Friday fold: a quartet from Marli Miller’s website
Marli Miller is a senior instructor at the University of Oregon. She is the author of Roadside Geology of Oregon and (with Darrel Cowan) Roadside Geology of Washington. She’s also a very talented geological photographer. She launched a website recently to showcase her work and make it available for instructors: Geology Pics. After chatting with Marli a bit in Flagstaff at the Rocky Mountain / Cordilleran section meetings of GSA …
7 May 2018
2/3 pass rate on determining geopetal “up”
A visual challenge via Twitter to determine stratigraphic younging direction ends with equivocal results. So let’s use GIGAmacro imagery to school your sedimentological students on how three primary sedimentary structures look different right-side-up versus up-side-down.
20 April 2018
Friday fold: Isoclinal in Damaraland
A guest Friday fold from Graham Andrews of West Virginia University: Graham describes this as an almost along axis view of a huge isocline in the Damaraland belt, Namibia Thanks for sharing! And a happy Friday to all.
10 April 2018
An outcrop showcasing a strand of the Kentucky River Fault System
Roadcuts in Kentucky show Ordovician limestones of two distinct types, replete with fossils and primary sedimentary structures, and juxtaposed by a fault, one strand in the Kentucky River Fault System.
6 April 2018
Friday fold: “wrecumbent in Wrangellia”
Darrel Cowan of the University of Washington has pitched in a Friday fold. Check this lovely scene out: Darrel says this is a recumbent fold in the Upper Triassic Nizina and Chitistone limestones. I took the photo when I worked for Shell in 1973 or 1974. I’m pretty sure it is on the west wall of the canyon occupied by the Root Glacier, several kilometers NW of McCarthy, Alaska. The …
Callan Bentley is an assistant professor of geology at Northern Virginia Community College. He is a fellow of the Geological Society of America and the President of the Geo2YC division of the National Association of Geoscience Teachers. Callan is a contributing editor at EARTH magazine and Past President of the Geological Society of Washington. He lives in the Fort Valley of Virginia.
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