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You are browsing the archive for 2010 September.

18 September 2010

Guest concretion

This was brought in last week by a student… It’s a broken concretion that she found in Des Moines County, Iowa, many years ago. She also had a slab of limestone with crinoid columnal fossils, and a broken geode from the same locality. I think this concretion is a thing of beauty, like a fossilized Gobstopper. I had to photograph it before I gave it back to her.

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17 September 2010

Friday fold: granite dikes, Barberton greenstone belt

Folded & boudinaged granite dikes in tonalitic gneiss, Barberton granite-greenstone belt, South Africa. From Passchier, CW, Myers, JS, and Kroner, A., (1990). FIELD GEOLOGY OF HIGH GRADE GNEISS TERRANES. Very crudely annotated: This is a sweet example of how you can get different structures developing in different orientations relative to the principal stress directions. In this particular part of the Barberton Greenstone Belt, compression (orange arrows) operated from the top …

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16 September 2010

Drilling: what, why, and how

As mentioned, I spent a significant part of last weekend was spent on a paleomagnetic sampling project with collaborators from the University of Michigan. On Friday, this was our field area: That’s the south slopes of Old Rag Mountain, a popular Blue Ridge hiking destination because unlike many Virginia peaks, when you get to the top, you see some rocks instead of 100% trees: But we didn’t come here for …

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15 September 2010

Aeolian sand in Hampton, VA

This video was produced by my friend Pete Berquist. It shows rapidly moving “sheets” of sand saltating down Grandview Beach in Hampton, Virginia, during high winds associated with Hurricane Earl. What do you notice here? A couple of things jump out at me, but I’d be curious to hear what this video makes Mountain Beltway readers think about…

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14 September 2010

The Blue Mosque

In Istanbul over the summer, Lily and I checked out the “Blue Mosque,” named for the predominant color of the mosaic tiles in its interior. It’s more formally know as “Sultan Ahmed Mosque,” named for the sultan who commissioned its construction in 1609. It is an elegant building: I loved the “pile of bubbles” effect of the multiple domes, and then the skyward piercing forms of the minarets. It also …

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12 September 2010

Scenes from a drill campaign

The past couple of days, I’ve been in the field, collecting samples with Dr. Fatim Hankard, a post-doctoral researcher from the University of Michigan, and Matt Domeier, a PhD candidate from that same fine school. We’re interested in using Virginia’s wealth of Catoctin formation feeder dikes to do paleomagnetism measurements that might help us constrain the latitude of Virginia during the emplacement of these dikes during the Neoproterozoic. More later …

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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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10 September 2010

Friday fold: Kinky metagraywacke from DC

Fourth edition of the “Friday fold;” second one via video. Happy Friday!

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9 September 2010

Mount Moran

The other day, Chris Rowan of Highly Allochthonous posted some pictures (and video!) of the Teton Range in Wyoming, a normal fault-bounded block of rock that has rotated along a north-south axis, with the west side dropping down and the east side rising up relative to the floor of Jackson Hole. This is classic “Basin and Range” extension, but the great thing about the Tetons is that it is so …

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8 September 2010

Lessons from a broken bottle

Whilst hiking at Dolly Sods over the weekend, I found this old artifact: Upper 10 is apparently a “Sprite”-esque lemon-lime soda, discontinued in America but still being marketed abroad. But that wasn’t what got me jazzed, of course. Look more closely… That is a lovely little conchoidal fracture, and it’s so exquisite because it preserves not only the concentric “ribs” that are typical of conchoidal fractures, but also delicate little …

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