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You are browsing the archive for mississippian (carboniferous).

3 August 2011

Gigapan of the French Thrust

To follow up on my March post on the French Thrust, here’s a gigapan of the outcrop. Sun River Canyon, Montana, of course: the Sevier fold-and-thrust belt.

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28 July 2011

A faulted chert nodule

Here is a trio of concentrically-zoned chert nodules in Mississippian Castle Reef Dolostone, exposed at Sun River Canyon, Montana, just downstream from the roadside outcrop of the French Thrust: If you look closely at the lowermost of the three chert nodules, you’ll see it’s been split and offset by a small fault. Here are close-up portraits of all three, concluding with the most interesting one (the deformed one): Hope all …

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12 July 2011

Stylolites in Mississippian limestone

Stylolites (pressure solution seams) in limestone of Mississippian age, exposed on the side of a rounded boulder in Hyalite Canyon, Gallatin Range, Montana. These stylolites, like most, are bedding-parallel, and thus most likely formed due to the weight of the overlying rock. Calcite, the dominant mineral, goes into solution under pressure, and insoluble material, like organic matter and clay, accumulates along the dissolution surface, producing a dark, wiggly line. Here, …

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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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25 April 2011

Two joints

Stopped at Sideling Hill, Maryland, a few weeks back with my three Honors students, on our way to Pittsburgh for the northeast/north-central GSA section meeting. Robin took this photo of me with some sandstone beds that reveal two nice examples of joint anatomy, complementary in their structure: First focus in on the area right of where my finger is pointing. It shows well-expressed plumose structure, little lines that point in …

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6 March 2011

French Thrust

That title sounds kinky, right? Well, calm down. I’m behind the curve on the latest Accretionary Wedge (as I was for the one before that), but here’s a quick image to join the parade of geologic photos that Ann is hosting. While it’s not my favorite, it’s definitely a favorite, more by virtue of the geology it shows than the aesthetic qualities of the image: That is an outcrop of …

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18 February 2011

Friday fold: Jefferson River Canyon

Here’s your Friday fold, straight from the canyon of the Jefferson River, near Cardwell, Montana. Perspective is to the south. East is on the left; west is on the right. Bigger version This is right next to the outcrops of LaHood Conglomerate that I mentioned earlier this week. My Rockies course co-instructor Pete Berquist and I bring the students here for several reasons, including the conglomerate, nearby Lewis & Clark …

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29 October 2010

Geology of the Richmond area field trip

On Saturday, after a fruitful 24 hours at the VCCS Science Peer Conference, my colleague Pete Berquist (of Thomas Nelson Community College) and I led a field trip to examine the geology of the Richmond, Virginia, area. We were joined by seven of our VCCS science-teaching colleagues and author Lisa Starr, a speaker at the conference. We started off by driving down to Belle Isle, an island located on the …

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11 September 2010

Fine faulting

Check it out: In the canyon of the Jefferson River, Montana, you can find yourself some limestone (Mississippian Madison Group, I think of the Lodgepole Formation) that has seen a wee bit of faulting: And here’s an annotated copy… Both of these images are enlargeable by clicking through (twice): Note the quarter for scale: this is very fine faulting (very small offsets). The thing that struck me as cool (and …

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18 May 2010

Falls of the James I: pluton emplacement

Last Friday, NOVA colleague Victor Zabielski and I traveled down to Richmond, Virginia, to meet up with Chuck Bailey of the College of William & Mary, and do a little field work on the rocks exposed by the James River. Our destination was Belle Isle, a whaleback-shaped island where granite has been quarried for dimension stone for many years. The island has also served as a Confederate prison for captured …

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