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6 September 2019

Friday fold: Gonzen, Switzerland

Science writer Gabe Popkin shared two fold photos with me this week – both from near Sargans, Switzerland, adjacent to the Rhine River Valley and the border with Lichtenstein. The photos shows the mountain called Gonzen. There, Jurassic limestones crop out in a very wavy pattern: I don’t know the geology of this area in any kind of detail, but I decided to trace out a distinctive upper surface of …

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27 July 2019

Offset limestone layers at Broom Point

Yesterday, I featured some folds from Broom Point, but there are also faults there. With the intriguing local limestone conglomerates providing easily-discernible marker beds, these apparently vertical faults are easy to spot. Here are three examples:

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26 April 2019

Friday fold: Black Sands Beach

The Friday fold can be found in a boulder of gray chert layers on Black Sands Beach, at Marin Headlands in California.

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14 February 2019

Friday fold: an arch of gypsum in Sicily

Ahh, Sicily on a Friday morning. Join us to examine a spectacular arch of gypsum from the Messinian evaporite package.

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21 November 2018

Brittle overprinting ductile in the South Mountains metamorphic core complex, Phoenix, Arizona

Today, we take a look at the structural geology that reveals the deformation evolution (first ductile, then brittle) of the South Mountains metamorphic core complex, south of Phoenix, Arizona. Expect lots of photos of smeared-out rocks, broken by faults.

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17 November 2018

Flow banding in pseudotachylyte, South Mountains, Arizona

Watch the flow of frictional melt in a “fossil earthquake,” frozen in time atop the South Mountains metamorphic core complex in Phoenix, Arizona.

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16 August 2018

A suite of deformational features in Lancaster limestones

In the Landisville Quarry, Lancaster, Pennsylvania, there is a quarry that cuts into Cambrian limestones. (The exact identity of these limestones is apparently a matter of some dispute, but that’s not going to stop us!) I visited the quarry in June on a field trip offered through the NAGT’s Eastern Section annual meeting. We witnessed multiple varieties of deformation there. First off, there was straight-up brittle extension, resulting in bedding-perpendicular …

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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.

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23 March 2018

Friday fold: Snow day edition

Snow may have cancelled the geology class, but there’s plenty to see outside! Join us for a tour of three fine examples of physical analogues in snow that show deformation akin to that we observe in rocks under tectonic stresses.

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23 January 2018

A kid and his slicks

On a family hike, Callan’s son finds some interesting smooth lines on a rock. What are they? What do they tell us? Tune in for a brief history of Appalachian geology.

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