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8 December 2017

Friday fold: Alpine cross sections by Albert Heim

The Friday fold is a figure from a 1922 book about the geology of the Alps by Swiss structural geology genius and artistic master Albert Heim. Marvel at his gorgeous depiction of the internal and long-since-eroded structure of these mighty mountains.

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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.

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24 November 2017

Friday fold: Idaho Springs Fm. amphibolite

Here’s a guest Friday fold from reader Carl Brink: Carl tells me that this is: Precambrian Amphibolite schist float boulder from the Idaho Springs Formation in Rist Canyon west of Fort Collins, Colorado.  Knife is 2.25 inches long. Thanks for sharing, Carl!

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10 November 2017

Friday fold: soft sediment deformation in California’s Castaic Formation

The guest Friday fold comes to us from the Miocene of California, deposited in a releasing bend basin along the San Andreas Fault.

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3 November 2017

Friday fold: More kinks from Glacier National Park

This Friday, let’s return to Glacier National Park. Here are some folds in Helena Formation limestone: Can’t see them? Fair enough – the point of maximum inflection appears to be hidden behind a snow-filled gully: But in addition to that big fold, there are several kink bands in there, too. Let’s zoom in: Here they are: Zooming in further, on the right-most of these kink bands: …And here, with the …

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27 October 2017

Friday fold: Quantankerous veins

What does it mean for a vein to be “quantankerous?” Well, to start with, it’s quartz. Second, it has to be disagreeable or cantankerous. This vein, seen in meta-arkose of the Catoctin Formation near the summit of the Blue Ridge at Rockfish Gap (not Afton Mountain), is such a quantankerous individual: You’ll notice its “S” shape, which might imply top-to-the-left kinematics. But just down the outcrop is this set of …

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20 October 2017

Friday fold: Kink folds in Glacier National Park, part II

Over the summer, I treated you to a great big kink fold in the sedimentary rocks of Glacier National Park. Here’s another set: Did you see both of them in that first picture? – one bigger down below, one smaller up above. Both kink bands dip to the left. Let’s zoom in on the upper one: There’s more where this came from – stay tuned for more…. and in the …

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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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