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12 April 2010

Accretionary wedge reminder: April 23

A friendly reminder that I’ve volunteered to host the next edition of The Accretionary Wedge, and I’ve chosen “heroes” as the theme. I invite all participants (geobloggers and geoblog readers alike) to contribute stories of their heroes. It’s time to pay tribute to the extraordinary individuals who helped make your life, your science, and your planet better than they would otherwise have been. The deadline for submission of posts will …


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11 April 2010

Quartz veins on Pimmit Run

Last Sunday, I took a solo hike along Pimmit Run in Virginia, accessing the valley via Fort Marcy, a Civil War fortification off of the George Washington Memorial Parkway. As always, I did a bit of geologizing along the route. One theme that emerged from the day’s photos was quartz veins. These veins form when the host rock (in this case, the Sykesville Formation) cracked open in a brittle fashion, …


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9 April 2010

Hol(e)y basalt, Batman!

Today, our theme is vesicles. Here are some images of vesicles in basaltic lava flows in the Owens Valley of California, the same spot where we saw the baked fanglomerate that I showcased a few days back. In this photo (and the zoomed-in detail shot below), you can see a couple of things. One is the size difference of the vesicles as you go up in the flow. Bigger bubbles …


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8 April 2010

Crystal ghosts

The first time I went to the Billy Goat Trail (Potomac, Maryland) with geology as the goal (as opposed to mere recreation), it was 2002. The trip was led by a professor at the University of Maryland. I was a graduate T.A. then, and didn’t know anything about the local geology. I remember at the end of the trip, the professor sent us out to search for “kyanite ghosts” (pseudomorphs …


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7 April 2010

The working life

It’s a rough life, working in the places I have to work… here are a few photos from yesterday’s field trip on the Billy Goat Trail with my NOVA Physical Geology students. Photos are courtesy Dr. Meg Coleman, who joined us for the hike. A post-lunch lecture on river incision (note the two prominent bedrock terraces, a.k.a. “straths” in the background): The crew climbing the dreaded “Traverse” section of the …


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6 April 2010

Suess effect II: corals sing an isotopic song

Almost a year ago, on my old blog, I brought up the issue of the Suess effect. Go read that post if you don’t remember what the Suess effect is. If you want an executive summary, digest this: The burning of low-14C fossil fuels (because the fuels are old and the 14C has all decayed), lowers the total atmospheric ratio of 14C relative to other isotopes of carbon. The carbon …


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4 April 2010

Easter egg

Searching through my photo archives this morning for something suitably “Eastery”… something in pastel colors, perhaps? … a petrified lagomorph? … how about an egg, or something egg-shaped? This is as close as I got: This is in the Owens Valley of eastern California, showing a boulder of the Mesozoic Sierra Nevada Batholith bearing a faulted xenolith. I love outcrops like this, with a combination of primary structures (like the …


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3 April 2010

Diatom time

Today’s EPOD is of a diatom. Seems like as good an excuse as any to share a couple photos of a big brass diatom sculpture from the American Museum of Natural History in New York. Finger for scale, but not really, since the sculpture isn’t to scale.


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Here, ptyggie ptyggie ptyggie!

Yesterday, I took my GMU structural geology class to the Billy Goat Trail, my favorite local spot for intriguing geology. Unlike last year, we managed our time well enough that we got to clamber around on the rocks downstream of the amphibolite contact. Here’s Sarah, Lara, Kristen, and Alan, negotiating a steep section: Justin, Joe, Nik, Aaron, Jeremy, and Danny find a chunky amphibolite boudin in metagraywacke. Notice how Jeremy …


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2 April 2010

Baked fanglomerate

A quick post to share a few images of an outcrop I visited last September out in California’s Owens Valley. This is a spot where alluvial fans coming off the eastern Sierra Nevada were overrun by a basaltic lava flow (Jeff, Kim, Fred, and Kurt for scale): The unofficial term for these conglomerates deposited by alluvial fans is “fanglomerate,” and it’s pretty cool to see the contact metamorphism at the …


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