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18 August 2022

Quarrying soapstone

Earlier this summer, I was lucky enough to visit a soapstone quarrying operation in Schuyler, Virginia, right on the Albemarle/Nelson County line. These soapstone bodies are metamorphosed ultramafic intrusions into the Neoproterozoic sedimentary deposits of the Lynchburg Group. The protolith peridotite sill crystallized at ~580 Ma, meaning the host sediments are older than that (but younger than the Grenvillian basement complex that underlies both). Then both plutonic rock and sedimentary …


29 May 2022

Accretionary wedge turbidites from the Lost Coast

The Lost Coast of northern California shows geological evidence of deep sea turbidity current sedimentation, tectonic accretion during Mesozoic subduction, and then isostatic uplift interacting with shoreline erosion. Check out a few photographs taken by Callan’s wife on a recent backpacking trip through the region.


15 April 2022

Friday fold: Cretaceous Canada

A guest contribution for the Friday fold, from reader Christian Gronau: Christian reports that this is located on the North side of Hwy.11, 20 miles east of Saskatchewan River Crossing, Alberta. Eastern foothills of the Canadian Rocky Mountains. Faulting and folding in Early Cretaceous Luscar Group sediments.  Typical repeating sequence of sandstone, siltstone and coal. Thanks for pitching in, Christian! Happy Friday to all!


17 July 2020

Friday fold: Sandy Hollow from the air

The Friday fold is spied below, in the Montanan landscape near Dillon, from an airplane high above…


6 March 2020

Friday fold: an Extreme(adura) geological history question

The Friday folds are revealed in an elegant cross-section through fantastic rocks in the Extremadura region of Spain.


28 February 2020

Friday fold: sandbox

The Friday fold is a lovely little sandbox analogue model by Prof. Marco Martins-Ferreira, who posted it on Twitter this week:  As deformation proceeds, you can see the layers develop folds that then morph into faults, shoving deeper layers atop more shallow strata. As a bonus, you can hear Marco’s baby cooing in the background! Here’s a stabilized, sped-up version, courtesy of Anna Williams:  Happy Friday, all!


18 October 2019

Friday folds from the Foreknobs Formation

TGIF! That’s my seven year old field assistant showing off the shape of a syncline in shale, siltstone, and fine sandstone of the Foreknobs Formation, a Devonian nearshore package of clastic sediment in the Valley & Ridge Province of eastern West Virginia. Want to see something freaky for Halloween? Photoshop can make it happen: Ewwww. Creepy! Another shot of the same fold, with a thick massive sand above a thicker …


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 …


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:


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.


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.


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.


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.


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 …


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.


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.


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.


30 December 2017

Normal faulting in the San Felipe Volcanic Field, New Mexico

A glance out the airplane window over New Mexico triggers a bit of web research and a new view of tectonic extension via Google Earth and geologic maps.


22 December 2017

The #FaultCup semifinals

Over the past few weeks, there’s been a fun game playing out on Twitter, hosted by Jorge (@lithospheric), called The Fault Cup, or #FaultCup in Twitterspeak. There’s a bracket showing one-on-one match ups between different faults, and then a 24 hour Twitter poll is posted, where the audience can vote for which one they want to advance to the next round.  Click through to embiggen. If you’ve missed the fast …


5 December 2017

The quarry in Contessa Gorge

Central Apennine stratigraphy and structure is on display in the wall of a quarry in Contessa Gorge, Italy. Have a look a nice normal fault and a submarine mass transport deposit.