structure

Accretionary Wedge #28: Deskcrops

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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).

Tavşanlı Zone field trip, part 3

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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: … Read more

Friday fold: twice-folded turbidites at Black Pond

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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 … Read more

Tavşanlı Zone field trip, part 2

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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 … Read more

Rumeli Hisarı

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Right after I got to Istanbul on this most recent trip, I took a taxi from my hotel down to the Bosphorus, to check out the Rumeli Hisarı, a fort complex built in 1452 by Sultan Mehmet the II in anticipation of the following year’s siege of Constantinople. It’s constructed at the narrowest point on … Read more

Photos from Virginia Geological Field Conference

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For the second year in a row, more exotic travel plans meant that I wasn’t able to attend the superb Virginia Geological Field Conference. I see that they have now posted some photos on the group’s Facebook page, so go check them out to see what we both missed last weekend. Here’s a taste: Sheared … Read more

Friday fold: multilayer buckle folding demo

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Check out this video I found online whilst uploading last week’s Friday fold: This video was produced and published on YouTube by Markus Beckers, Michael Ketterman, Dennis Laux and Janos Urai. It’s a nice demonstration of how multiple layers of material of different properties and different thicknesses can yield up different flavors of folds. In … Read more

Deducing my first anticline

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When I was done with my sophomore year at William & Mary, I embarked on a time-honored tradition among W&M geology majors: the Geology 310 Colorado Plateau field course. Jess alluded to this same course in her Magma Cum Laude contribution to this month’s Accretionary Wedge geology blog “carnival,” too. My version of Geology 310 … Read more

Friday fold: Siccar Point, Scotland

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As with last week, I’m going to show you someone else’s fold today. This one should have strong resonance with most geologists, because it’s a fold in the tilted (and contorted) older strata exposed below the famous unconformity at Siccar Point, Scotland: I found this image on the British Geological Survey’s online repository of images, … Read more

Building stones of the Haghia Sophia

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The Haghia Sophia (or “Ayasophia”) is an astounding building in old town Istanbul. It is an ancient cathedral turned mosque turned museum. Through all these incarnations, the Hagia Sophia has retained some features and had other ones added on: it is a palimpsest of architecture, symbology, and history. Walking through its soaring main chamber, or … Read more

Champlain thrust fault

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Over the summer, I went up to Vermont to visit my friends the Clearys. Joe Cleary is a college friend and a talented luthier. He and his wife Tree and their children Jasper and Juniper have settled in Burlington, a lively town with a lot of cool stuff going on. Joe took time out one … Read more

Friday fold: granite dikes, Barberton greenstone belt

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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 … Read more

Fine faulting

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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 … Read more

Mount Moran

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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 … Read more

Lessons from a broken bottle

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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 … Read more