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8 December 2015

Considering the Spechty Kopf diamictite

I have known for a long time about a diamictite in the latest Devonian part of the Appalachian stratigraphic sequence, since it is exposed in the lowermost part of the section (western end of the outcrop) at Sideling Hill, Maryland. When I led field trips there, I talked students through the multiple possible origins for diamictites (sedimentary rocks that are poorly sorted, with significantly “outsized” clasts “floating” in a finer-grained …

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1 December 2015

Which way’s up? Check cavity fills.

When snail shells are deposited in a bunch of sediment, they serve as tiny architectural elements, with a “roof” that protects their interiors. Any sediment mixed into the shell’s interior will settle out (more or less horizontally), and then there will be empty space (filled with water, probably) above that. As burial proceeds and diagenesis begins, that pore space may be filled with a mineral deposit, such as sparry calcite. …

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30 November 2015

Slump in progress on Corridor H

I was out on Corridor H last week, looking at rocks with my Honors student, and on the way back from the field work, I noticed this: Click to enlarge That’s a fresh slump scarp running across a slope that is gradually sliding downhill. (The left half of the image is moving down relative to the right.) To judge from the rip-rap-filled culverts, this slope must have a previously-documented history …

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27 October 2015

Corridor H virtual field experience

My Historical Geology class was in for a new experience for the semester’s capstone field trip. Before we headed out into the field (to the exceptional roadcuts along Corridor H in Grant and Hardy Counties, West Virginia), we had them examine all the outcrops virtually, in the comfort of the classroom, using digital imagery. I say “we” because this initiative was a collaboration with my colleague Alan Pitts, who developed …

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26 October 2015

Tool marks, trace fossils, and flute casts from the Brallier Formation

Another gem from Saturday’s Historical Geology field trip: the bottom of a fine sandstone bed in the Devonian Brallier Formation, showing a variety of primary sedimentary structures, including tool marks, trace fossils, and several flute casts. Current flow direction here would have been from upper left toward lower right. Here’s a version of the photo with a few of these features highlighted:

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25 October 2015

Cool fossils from the Clearville member of the Mahantango Formation

On Saturday, I took my historical geology class on their field trip out to Corridor H, West Virginia. We made a stop at the Mahantango Formation outcrop exposed on the eastbound exit ramp near Baker, and poked around there for fossils. These Devonian-aged siltstones are chock full of invertebrates including rugose corals, crinoids, articulate brachiopods, and even trilobites. Here are two of the best fossils we encountered there: A trilobite …

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12 October 2015

Bedding/cleavage GigaPans at Harpers Ferry, WV

I’ve been thinking lately about Harpers Ferry, the spot where West Virginia, Virginia, and Maryland meet, at the confluence of the Potomac River and the Shenandoah River. I’ve noted small outcrops of its overturned beddding here previously, and also described a book I read about the man who made the place infamous: John Brown. I went out there again last week with my NOVA colleague Beth Doyle, and we explored …

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5 October 2015

Trace fossils in the Juniata and Tuscarora Formations

Route 33 in Pendleton County, West Virginia cuts across the lower Paleozoic stratigraphic section. I went there this past spring on a sedimentology and stratigraphy field trip with the GMU sed/strat class. The trip was orchestrated by professor Rick Diecchio. Here are some scenes from two of the stops – the upper Ordovician Juniata formation (red sandstones and shale intepreted as Taconian molasse) and the overlying Silurian Tuscarora Formation (thick …

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29 August 2015

Mystery structure: please help identify / interpret

I have a mystery for you today: These are samples of Tonoloway Formation carbonate (not sure if it’s limestone or dolostone in retrospect), with bedding more or less horizontal in these images, and a few petite stylolites running orthogonal to that. The top sample has a gentle fold 2/5ths of the way across. All of the samples are from the same site in West Virginia, along Corridor H. I’m wondering …

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20 August 2015

Stromatoporoids in a Devonian reef

Here are a few shots of a Devonian aged reef exposed in Mustoe, Virginia – one of the sites I visited this spring with GMU’s Rick Diecchio, when he led his sedimentology and stratigraphy trip there. At first, the outcrop made no sense to me – I kept searching for bedding, and failed to find it. Then, the reef interpretation clicked, and suddenly I didn’t “need” bedding any more… Stromatoporoids …

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