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17 August 2018
Friday folds: Moomaw Reservoir outcrops
Break out your paddle and sunhat. We’re going kayaking on Lake Moomaw, in search of Friday folds…
10 August 2018
Friday fold: Gnarly chert from Spy Rock
The Friday fold is an outcrop of folded chert from the Franciscan mélange in Mendocino County, California. (It should look familiar to anyone who’s ever visited Marin Headlands near San Francisco.)
3 August 2018
Friday fold: a recumbent set of turbidites in the Black Hills
Today we feature a famous recumbent, chevron anticline near Hill City, South Dakota has been featured as a Friday Fold or not, but thought I would give it a go. The rocks are Proterozoic metagreywacke turbidites with 70 complete or partial Bouma sequences. This is believed to be a late (D4) fold in the Black Hills related to upward doming associated with the emplacement of the Harney Peak Granite, which …
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: …
20 July 2018
Friday fold: Alpine peak containing a high elevation recumbent fold
Via Twitter, a Friday fold from Maddy Rushing: #FridayFold, @callanbentley? pic.twitter.com/eaKIuuvFgB — Maddy Rushing (@komaddyite) May 25, 2018 This is in the Alps of Switzerland; I don’t know more about it than that. If you recognize the site or the geology, educate us in the comments!
13 July 2018
Friday fold: the anticline at Chickie’s Rock
Chickie’s Rock is a prominent cliff of Cambrian quartz arenite (sandstone) in Lancaster County, Pennsylvania. I visited it last month with field trippers at the eastern section meeting of the National Association of Geoscience Teachers. One of the aspects of the site is this gentle anticline with axial planar cleavage: The yellow rectangle is my field notebook for scale. Another shot: Happy Friday to all!
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 …
22 June 2018
Friday fold: Connemara Marble, Ireland
Another guest Friday fold (keep ’em coming, folks!) – This time from Eric Pyle of James Madison University: This is a weathered outcrop of the Connemara Marble in western Ireland, about a meter wide. Thanks for sharing, Eric!
15 June 2018
Friday fold: scenes from the Schilthorn cable-car
My friend Karen Aucker from NAGT’s Eastern Section shared these images (and a video!) of the folds she glimpsed from the cable-car on her way up the Schilthorn in Switzerland. I reckon they will do for our Friday fold: Thanks for sharing, Karen! These are great. Happy Friday, all!
9 June 2018
Friday fold: contorted carbonates of the Conestoga Formation
Today, in Millersville, Pennsylvania, on the campus on Millersville University, I saw these contorted carbonates. They are of the Cambrian Conestoga Formation, and I saw them on a NAGT Eastern Section field trip led by Lynn Marquez of Millersville University. This deformation is purported to be Taconian, but it looks very much like Alleghanian deformation in similar aged and composition rocks in Virginia. Interesting!
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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