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13 October 2017

Friday fold: ptygmatic vein from Finland (NMNH)

Happy Friday! Here’s a sample from the Smithsonian Institution’s National Museum of Natural History in DC: As the label says, we have a nice example of ptygmatic (“intestine like”) buckle folding here. It comes from Finland. The coarse equigranular crystals in the vein appear to be mainly potassium feldspar and quartz. The surrounding matrix has a pronounced foliation. Note the cuspate “flames” of matrix between the broad “lobes” of folded …

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6 October 2017

Friday fold: recumbent isoclinal folds in Saruratown Mtn window, NC

Here’s a cool fold pair that rolled through my Twitter feed today: 2nd day Appalachian field trip. Recumbent isoclinal folds on a clear morning at Sauratown Mtns window NC pic.twitter.com/sHkmbp6roh — Joe Allen (@CU_in_the_field) October 6, 2017 Joe Allen gave me permission to share it with you here. Here’s the photo with bedding traced out (by me)  in yellow: Happy Friday, all!

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29 September 2017

Friday folds: soft sediment deformation in thin sections of MTD sandstone

The Friday folds are small soft-sediment deformational features within a dismembered, folded sandstone (a “ploudin”) from a mass transport deposit from the latest Devonian of West Virginia.

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22 September 2017

Friday fold: bend in a vesicular lava flow, Etna

It’s the First Friday of Fall! Here’s a sort of fold to help you celebrate: a section through a ∧ shaped bend in a vesicular basalt flow from the eastern flanks of Mount Etna in Sicily. It’s due to volcanic lava flowing rather than ductile deformation of a pre-existing solid rock (our usual habit with this feature), but I think we can appreciate it regardless:

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15 September 2017

Friday fold: Dextral asymmetry in a shear zone, Italy

The Friday fold comes from highly foliated rocks in a shear zone near Tyrol, Italy. It was contributed by reader Samuele Papeschi.

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8 September 2017

Friday fold: Ptygmatic folding in gneiss

I was transferring some samples into my structural geology cabinet last week when I found this beautiful ptygmatic (“intestine-like”) folded quartz vein. I thought it deserved some wider circulation. I can’t recall where it came from, but it’s beautiful, with a train of a dozen or so isoclinal folds. So I made the digital media you see below. Enjoy! Here’s a GIGAmacro of the sample (you need Flash enabled to …

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25 August 2017

Friday fold: Villa Romana di Casale

Okay, I’ll admit this is a bit of a stretch, but here’s your Friday fold: The mosaic-covered floor of this long hallway in the Villa Romana di Casale in central Sicily shows profound warping. The middle shadowed area sags downward by at least a meter, maybe more. It’s not a geological material that’s been deformed, but an architectural element instead. Still: the principle of original horizontality applies to floors as …

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18 August 2017

Friday folds: the Roman Forum

When in Rome, do Friday folds as the Romans do? Here are some images from my brief, sweltering visit to the Roman Forum(s) this past summer. The whole region is a jumblepile of ancient ruins in a thousand styles. Almost nothing is labeled. It looks like this: This particular building held up a bit better, and its lovely columns sported some folded marbles: Close-up shots to show the folding internal …

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11 August 2017

Friday fold: Eagle Rock

For the Friday fold, Callan digs out images of Eagle Rock, Virginia, well aged in his digital archive for a decade!

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4 August 2017

Friday fold trio: Samples from UNM, ABQ

It’s Friday and that means “fold time” here at Mountain Beltway. Today, we feature a trio of samples on display in the halls of the Department of Earth and Planetary Sciences at the University of New Mexico.

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