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15 May 2015

Friday fold: Crumpled Carboniferous cyclothems

Friday fold: Crumpled Carboniferous cyclothems

Twitter follower Bob J. submitted this week’s Friday fold: Carboniferous cyclothems at Scremerston, Northumberland. Thanks Bob!

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8 May 2015

Friday fold: Foreknobs formation

Friday fold: Foreknobs formation

Last one in the triumverate sent in by reader Eric Fulmer: Annotated: Happy Friday and (for many of you) happy end of the semester!!

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1 May 2015

Friday fold: Tight syncline/anticline pair in Brallier Formation

Friday fold:  Tight syncline/anticline pair in Brallier Formation

The Friday fold shows clastic detritus (turbidites or “flysch” from the Acadian Orogeny) crumpled into tight folds due to the later Alleghanian Orogeny.

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24 April 2015

Friday fold: Bloomsburg Formation at lime kilns on C&O Canal

Friday fold: Bloomsburg Formation at lime kilns on C&O Canal

Milepost 127.4 (High, 2001) on the C&O Canal: …Cool if you’re into history. …Cool if you’re into economic geology. …Cool if you’re into Friday folds!   Reader Eric Fulmer sent me this photo (along w/ two others you’ll see in weeks to come). Thanks, Eric!

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27 March 2015

Friday fold: Isla Escarpada, Chile

Friday fold: Isla Escarpada, Chile

I’m very nearly delinquent on posting the Friday fold… Here you go – a Google Earth view of a differentially-weathered fold partly above and partly below sea level in Chilean Patagonia, south of Puerto Natales: They call it Isla Escarpada. Awesome. Here’s a Google Maps link if you want to explore it yourself. Happy Friday!

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20 March 2015

Friday fold: flexed turbidites

Friday fold: flexed turbidites

Spring is almost here! As you get ready for the equinox, enjoy this gentle fold on a Friday: These are turbidites (graywacke and shale) of the late Ordovician Martinsburg Formation, seen in Edinburg Gap, western Massanutten Range, greater Shenandoah Valley, Virginia. Bedding is flexed very slightly here, from moderately-dipping to more steep, and then back to moderate again. Slickensides on the top of some exposed layers indicate the beds shifted …

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6 March 2015

Friday fold: Mazatzal Orogeny, Arizona

Friday fold: Mazatzal Orogeny, Arizona

Reader Mike Pendergrass contributes this Friday’s fold: I found your blog a couple years ago and I share your love of structural geology.  I did my Master’s Thesis while at Northern Arizona University in the early 80’s and mapped an area on the Mazatzal Mountains of central Arizona.  The Mazatzals in my field area contain metasedimentary rocks that were deformed in the Mazatzal Orogeny (~1.6-1.7 billion years ago).  The stratigraphy …

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27 February 2015

Friday folds: Three tweets

Back at the beginning of January, I asked for help on Twitter for Friday fold fodder. Here are three responses I got: @callanbentley one of my favorites from South Georgia Island. Have more on the laptop. pic.twitter.com/UaRtxM77Vm — John Van Hoesen (@Taconic_Musings) January 8, 2015 @callanbentley 2 folds from my SC Inner Piedmont MS thesis mapping field work (1997). biotite gneiss and amphibolite. pic.twitter.com/cnoyzwK3cL — Doug (@dropstones) January 8, 2015 …

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13 February 2015

Friday fold: Ptygmatic Irving Fm., Colorado

Friday fold: Ptygmatic Irving Fm., Colorado

Another one from Kim: Kim says: Pygmatic folds in the Precambrian Irving Formation. I think this is 1.7 Ga deformation, late in the Yavapai orogeny, which added various arcs in Colorado to North America. Good place to think about strain ellipses in progressive deformation. Zooming in on the best part, and dialing up the contrast a bit: That’s intense! Seriously strained rocks. What fun!

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6 February 2015

Friday fold: Ouray Limestone, Colorado

Friday fold: Ouray Limestone, Colorado

Kim Hannula shares a fold today: Kim says: The rocks folded here mostly the Devonian Ouray Limestone. There’s a fault through the outcrop, and another fault to the left of the photo. Regionally, the faults are mapped as normal faults, mostly with the east (right in photo) side down. Locally, that’s not what I see in this outcrop, which makes this a funky place to look at a fold with …

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