Callan Bentley

Nice plume

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Another scene from the South Page Valley Martinsburg outcrop featured here last week: a slightly mud-bedecked example of plumose structure. This plume occurs within a single graded bed (turbidite) of the Martinsburg Formation. It gets younger (paleo-up) to the right. The joint propagation that the plumose structure records began somewhere vertically above the area of … Read more

Mystery fossil (?) for crowd-sourced identification

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A Fort Valley neighbor brought me this sample yesterday, asking me to tell her what it was. But while my brain’s pattern-recognition centers lit up when examining its “rows” of scale-like bumps, it didn’t match up with anything that I know from anywhere else here. Take a look, and click any of these images to … Read more

Two new GigaPans of Rockfish Gap, Virginia

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I took a trip down to Charlottesville this week for a couple of meetings, and I made time along the way to capture two new GigaPans of the lovely exposures of Catoctin Formation greenstone at Rockfish Gap, where Interstate 64 traverses the Blue Ridge. This is very close to the southernmost tip of Shenandoah National … Read more

GigaPan suite from the South Page Valley Martinsburg Outcrop

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Are you into structure? Sedimentology? Stratigraphy? Well, I’ve got some good news for you – I’ve imaged several key outcrops on the newly-discovered (to me) roadcut on South Page Valley Road, showcasing the middle Martinsburg Formation turbidites (and their Alleghanian structural overprint). link link link link link link See if you can find: an anticline … Read more

“Outcrops” on the barn at Peirce Mill, DC

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The Friday before last, I was in DC for a fun geology/botany field trip, and I got the opportunity to stroll around the barn at historic Peirce Mill, a historical grain mill along Rock Creek in Rock Creek Park, Washington, DC. The barn is immediately south of Tilden Street NW. It appears to have been … Read more

Incipient boudinage in overturned Edinburg Formation

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Boudinage is such a fun structure. Here’s an example from the roadcut adjacent to the quarry featured so heavily last week. The thick limestone stratum in the center of the photo has been stretched left-to-right. It exhibits pinch-and-swell structure, the first stage of boudinage. Small extensional fractures began to form in the boudin necks, accommodating … Read more

Skunk Cabbage

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On Friday, I took a field trip to DC with Geologic Map of the Washington West Quadrangle author Tony Fleming, City of Alexandria Natural Resource Specialist/Plant Ecologist Rod Simmons, and a host of interested folks from many different professions and localities. We were interested in looking at ecological relationships between rocks and plants, and had … Read more

Introducing SmartFigures

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Previously, I’ve hinted that I was working on a top secret special project for Pearson Education. Now that the books have been published, I wanted to take a moment to discuss the details of the project. In the newest editions of both Earth: An introduction to Physical Geology (Tarbuck, Lutgens, & Tasa, 2014) and Foundations of … Read more

Friday fold: the case of the strangely stout stylolites

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Today, we return to my field trip from last week, for a look at an odd outcrop of the Ordovician-aged Edinburg Formation: Note the car key with green lanyard, to provide a sense of scale. It’s folded, as the yellow bedding traces show in this annotated version: But what really caught my eye about this … Read more

Slicks in Cub Sandstone

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During Alleghanian deformation (late Paleozoic), the Cub Sandstone we looked at yesterday was tilted to near vertical at Catherine Furnace. The shale layers developed cleavage at this time, and there was evidently some flexural slip between sandstone layers, to judge from these fine slickensides: Students: Can you deduce the sense of motion from the orientation … Read more

Upper Martinsburg “Cub Sandstone” in GigaPan

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Today, two GigaPans shot of the uppermost Martinsburg Formation, informally known as the “Cub Sandstone” since it crops out along Cub Run in the southern part of the Massanutten range. 10 or 15 meters upsection (west) of these two outcrops is the base of the Silurian-aged Massanutten Sandstone, the ridge-forming unit. Lower in the section: … Read more

A closer look at the recumbent anticline from last Friday

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Last week, the Friday fold was presented in GigaPan format only, which led to a concerned reader lamenting that he couldn’t see it on his mobile device. (GigaPans are Flash-based images; they don’t work on Apple devices in the standard GigaPan format, though there is a perfectly suitable workaround with two extra clicks.) So, for … Read more

Bouma ABE

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The initials ABE might make you think of Lincoln, but that’s not what I’m talking about. Today, the letters mean something else: three subdivisions of the 5-part Bouma sequence of turbidites. I took these photos on a new (to me) outcrop of the Ordovician-aged Martinsburg Formation in Page County, Virginia. I visited the site for … Read more

Friday fold: a recumbent anticline in an abandoned quarry

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Yesterday, I spent a pleasant day in the field with John Singleton, the new structural geology professor at George Mason University. I was showing John a couple of sites I’ve used as field trip locations for the GMU structural geology class, and John was showing a couple of new sites to me – places he … Read more