You are browsing the archive for Friday Fold Archives - Mountain Beltway.
8 December 2017
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.
24 November 2017
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!
10 November 2017
The guest Friday fold comes to us from the Miocene of California, deposited in a releasing bend basin along the San Andreas Fault.
3 November 2017
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 …
27 October 2017
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 …
20 October 2017
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 …
13 October 2017
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 …
6 October 2017
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!
29 September 2017
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.
22 September 2017
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: