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You are browsing the archive for geology Archives - Page 2 of 14 - Mountain Beltway.

6 January 2012

Friday fold: the Contorted Bed

Callan reviews the geology of the superlatively auriferous Witwatersrand Supergroup of South Africa, and then zooms in on a distinctive marker bed near the base of the sequence. The deformation in this particular banded iron formation (BIF) is an aesthetic wonder, as this suite of images reveal. The layer outcrops in the heart of urban Johannesburg.

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27 October 2011

Pavement outcrops of strained Seine conglomerate

Picking up from the astonishing first couple of outcrops we saw of strained Seine Group metaconglomerate from the boundary between the Wabigoon and Quetico sub-provinces of the Superior Craton, our group moved on down the road. It was lovely clear fall weather near Fort Frances, and shockingly warm. Our third stop of the morning was a lunch stop atop a great “pavement” outcrop of the same strained metaconglomerate, showing different …

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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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7 June 2011

The grave of John Wesley Powell

Callan visits the grave of John Wesley Powell, second director of the USGS and explorer of the Grand Canyon, on an afternoon in Arlington National Cemetery.

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10 May 2011

Four new gigapans from the Billy Goat Trail

Yesterday afternoon, I spent some time in the field with a colleague, a student, and a gigapan. I took four gigapan images, which are of varying quality due to the partly cloudy day, but still you ought to find them interesting to explore. You can see any of them full-screen by clicking on the word “GigaPan” in the lower right corner: Antiform in Mather Gorge Formation, C&O Canal: Folds and …

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30 March 2011

Rusty rinds on peely rocks

Another group of interesting cobbles from the same sand and gravel pit that I described earlier in the week: Here’s the same sample, gone all animated, for your perspectivizing pleasure: What we’re seeing here is some fine-grained gray colored rock (siltstone, I guess?) that’s developed a pronounced weathering rind marked by a large amount of rust. This rusty rind is tougher than the original, unaltered rock, and it peels off, …

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29 March 2011

Tillite in outwash

Hoo boy. This one made me yelp… While on the glacial geology of western Pennsylvania trip last Saturday, we visited a gravel quarrying operation. The operators were extracting gravel from a glacial lake delta deposit, and it was full of glacial outwash — sediments washed out from the melting front of the Erie lobe of the Laurentide ice sheet. We were there to look at the Pleistocene features, but several …

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16 March 2011

Video book review: Roadside Geology of Maryland, Delaware, and Washington, D.C. by John Means

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12 March 2011

The morning after

A new resource for the Japanese earthquake is online this morning, a “supersite” similar to the ones that exist for other huge events. Checking it out this morning, I found some interesting stuff. Over night, there have been more aftershocks, and here’s the most recent 600 or so events in the area, taken from IRIS’s interactive map. You can see the big circle that represents yesterday’s main shock: Explore the …

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21 February 2011

Mount Washington 1

Callan begins a new series on the geology of Mount Washington, New Hampshire with a look at a roadside outcrop of metamorphic rock bearing enigmatic inclusions. Tourmaline-bearing pegmatites are also spotted.

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