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30 October 2010

Orbs in the floor

Orbs in the floor

Happy Saturday morning, everyone. I’m on my way down to the National Mall for fellow Tribesman Jon Stewart’s “Restoring Sanity” rally, but I thought I would just quickly post a little geological treat for Mountain Beltway readers. These are pisolites (basically like a big oolite, but without the biological component that would qualify them as oncolites), as seen in the travertine panels that make up the floor of the conference …

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29 October 2010

Friday fold: contorted Sivrihisar marble

Friday fold: contorted Sivrihisar marble

Highly contorted laminations in a blueschist-grade marble, Sivrihisar massif, Turkey.

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Geology of the Richmond area field trip

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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28 October 2010

Accretionary Wedge #28: Deskcrops

In honor of this month’s Accretionary Wedge (geoblog carnival; this month the theme is “deskcrops”), I recorded the following short video, showcasing some samples I have in my office: stromatolite (western Montana), conglomerate (Patagonia), schist (New Hampshire), anorthosite (New York), amygdular meta-basalt (Virginia), amphibolite (California), hematite concretions (eastern Montana), and a stretched-pebble lineated meta-conglomerate (Turkey).

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The tale of the hammerheaded copper tadpole

The tale of the hammerheaded copper tadpole

Okay, now just what the heck is going on in these pictures? (All of them can be enlarged by clicking through.) The photos are different views of the same crystal. It is a broken hexagonal prism of quartz, fading to amethyst at the distal end, found by Doug Dupin of northwest DC during the excavation that led to the Palisades Museum of Prehistory. The crystal is about 3.5 cm long, …

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26 October 2010

Tavşanlı Zone field trip, part 3

Tavşanlı Zone field trip, part 3

Picking up where we left off last time, we were in some partly-serpentenized peridotite, part of the Burham Ophiolite in Turkey’s Tavşanlı Zone, an ancient tectonic suture. Our next stop on the field trip allowed us to visit some diabase dikes: Here’s a close-up of the right contact of the dike with the host peridotite: The field notebook’s long edge is ~18 cm. And here it is again, annotated: Near …

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22 October 2010

Friday fold: twice-folded turbidites at Black Pond

Friday fold: twice-folded turbidites at Black Pond

Today’s Friday fold comes to us courtesy of Gary Fleming, botanist extraordinaire and brother of Tony Fleming, geological Jack of All Trades. Together, the Fleming brothers led a field trip for the Geological Society of Washington. While I was on that field trip, the topic of polyphase deformation came up, which led a couple of weeks later to Gary sending me this photograph. He took this photo in the Black …

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21 October 2010

Tavşanlı Zone field trip, part 2

Tavşanlı Zone field trip, part 2

Yesterday, I shared a few thoughts about the first couple of stops on the field trip I took earlier this month from Istanbul to Ankara, prior to the Tectonic Crossroads conference. Today, we’ll pick up with some images and descriptions from the next few stops. After lunch, our next stop brought us to a relatively low-metamorphic-grade outcrop of sheared graywacke (dirty sandstone) and shale. As you can imagine, it wasn’t …

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20 October 2010

Tavşanlı Zone field trip, part 1

Tavşanlı Zone field trip, part 1

Before the Tectonic Crossroads conference two weeks ago, I had the good fortune to participate in a Istanbul-to-Ankara geology field examining the Tavşanlı Zone, a tectonic suture zone where a portion of the Tethys Ocean basin closed. This paleo-convergent boundary is marked by a suite of interesting rocks, including blueschists, ophiolites, and eclogites. I’d like to share with you some of the things I saw along the trip. This is …

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17 October 2010

Birthing a litter of drumlins

Birthing a litter of drumlins

Quite appropriately, Glacial Till won the new the latest edition of “Where on (Google) Earth?”, hosted here yesterday. The location I picked is the subject of a new paper by Mark Johnson and colleagues appears in the current issue of Geology (October 2010). It shows a place in Iceland where a piedmont-style outlet glacier called Múlajökull is pooching out to the southeast from the Hofsjökull ice cap. Here’s a more …

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