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11 July 2011

Concentric ribs on a joint surface

Cretaceous sandstone layers, exposed on the Blackfeet Reservation (Montana route 49), east of Glacier National Park, Montana. Apparently these two are the opposite halves of the same jointed block.


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10 July 2011

Cascade Canyon

Following up on Friday’s fold, I wanted to share a few other images from our hike last week in Cascade Canyon of Grand Teton National Park.  Lots of cool exposures of Archean basement rock there. Folds in gneissic banding: Big, angular mafic blocks in a felsic soup: Swarm of granite dikes on a mountainside: Asymmetric feldspathic porphyroclast in amphibolite, with apparent reaction rim: Boudinage and an isoclinal fold: Ptygmatic fold: …


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8 July 2011

Friday fold: basement waves

Spotted this in Cascade Canyon, in the Tetons of Wyoming, last weekend: Nice asymmetric antiforms and synforms in the gneissic layering of the Archean basement rocks exposed there. Also, we saw a bull moose. More on that later on, when I get more time.


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5 July 2011

Varves from Yellowstone Lake

The other day, driving south through Yellowstone on our way to the Tetons, I stopped to give my students the obligatory look over Yellowstone Lake’s West Thumb, looking east towards the snowcapped Absaroka Range in the distance. But in addition to a lovely view and a few birds, we found something really cool… Those are varves, seasonally-laminated couplets of sediment (light = summer; dark = winter) that are made of …


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1 July 2011

Friday fold: west Bighorn monocline

While out in the field with Butch Dooley last week, making major discoveries like I do, I was very impressed with the landscape-scale west Bighorn monocline, which takes formerly horizontal Madison limestone and skews it to a westward dip where the mountains end and the intermontane basin begins. It’s totally sweet. Check it out in photo form and gigapan, too.


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