You are browsing the archive for mesoproterozoic Archives - Mountain Beltway.
2 August 2019
The ‘Friday fold’ shows gorgeous conjugate sets of kink bands transecting the plane of foliation in some phyllitic metasediments seen on the southern Burin Peninsula of Newfoundland.
27 July 2018
Hiking Siyeh Pass in Glacier in Glacier National Park on Tuesday with my Montana State University field course, we spotted a few new folds in the Empire Formation (a transitional unit between Helena Formation and Grinnell Formation). Here is one of the students serving as a sense of scale, with interesting features on either side of him: On the left, there are small scale folds in a regular little train: …
28 July 2017
It’s Friday! How about we celebrate with a beautiful kink fold from a gorgeous national park?
15 April 2017
My son and I hiked Compton Peak in Shenandoah National Park this morning, and saw these two lovely examples of xenoliths. The example above is small, but it shows clearly the difference between the coarse, felsic basement rock (Mesoproterozoic granitoid, comprising the xenolith) and the surrounding fine-grained dark green metabasalt of the Catoctin Formation (Neoproterozoic). Here’s another, bigger example: These two Blue Ridge examples both illustrate the principle of relative …
29 October 2016
In Shenandoah National Park, astride Virginia’s Blue Ridge, feeder dikes of Catoctin Formation (meta-)basalt cut across the Grenvillian-aged granitoid basement. Due to their mafic composition and columnar jointing, these feeder dikes generally weather more rapidly than their host rocks. I led a field trip in the park on Thursday for my son’s school, and my student Marissa was there the weekend prior, checking out the autumn leaves and geology with …
16 September 2016
The Friday fold is a guest submission from Bill Burton, who took the photo of these lovely ptygmatic folds in migmatite in a national park on the 100th anniversary of the founding of the Park Service.
27 March 2016
Here are three more of my Photoscan-generated, Sketchfab-hosted 3D models of rock samples: Mud cracks in Tonoloway Formation tidal flat carbonates, Corridor H, West Virginia: Diorite from the eastern Sierra Nevada of California: Vein cross-cutting foliated & lineated gneiss, Blue Ridge basement complex, Virginia:
12 August 2015
As longtime readers know, late summer is when my Rockies students submit their final projects – web-based explanations of key geologic sites they examined during the trip. Today, I offer you a guest blog post by student John Leaming. You’ll notice that I’m not *completely* absent from the post, however – I make a couple of cameos as “sense of scale.” Enjoy, -CB ______________________________________________________________ Glacier National Park, Belt Supergroup I …
30 July 2015
My favorite place to have lunch in Montana is at the Grinnell Glacier cirque in Glacier National Park. This is the dining room table: You’re looking at a bedding-plane-parallel exposure of Mesoproterozoic stromatolites here. Every few years, I’m lucky enough to hike up there with motivated students and share food atop this unparalleled view into the shallow seas of more than a billion years ago. Stromatolites are sedimentary structures that …
22 July 2015
Another gem from the Grinnell Glacier cirque: Zooming in on the contact, showing the concentrically-zoned ooids: Near the tip of the flame structure (?), I noted alignment of longer platy / flaky components within the oolitic layer: This looks like a loading structure – soft sediment deformation due to a density inversion – perhaps when some high-energy event (a storm?) dumped a bunch of relatively coarse ooids atop some squishy …