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11 December 2011
Just the thing for a winter day on the east coast…
… a brief glimpse of summer in the Rockies: [youtube=”http://www.youtube.com/watch?v=hbRx7W1nYUk”] Footage shot south of Blacktail Butte, in Jackson Hole, looking west towards the Teton Range, in Wyoming. July 2011. Gros Ventre River terrace in the mid-ground.
15 October 2011
Cross-bedding in Flathead Sandstone, Wind River Canyon
This is a boulder of Cambrian-aged Flathead Sandstone, the unit overlying the Great Unconformity exposed in Wind River Canyon, Wyoming. Click to make it 5000 pixels wide. Swiss Army knife for scale. It shows a lovely example of multiple upside-down cross-beds. It also shows a heavy layer of caliche on what is (now) the upper surface – a phenomenon which typically occurs on the underside of sedimentary clasts. So not …
5 October 2011
Two Sisters
All this talk about footprints and tail traces, and I haven’t even shown you any “for sure” dinosaur fossils. Well, let’s remedy that today. We return now to the scene: exposures of the Jurassic Morrison Formation, on the east side of the Bighorn Basin, just north of Shell, Wyoming. I was wandering around, finding things like ripples and lichens and cobbles of chert that had multiple intersecting conchoidal fractures, and …
4 October 2011
Tall tail
Okay, so I was out photographing ripples and admiring lichens, and then I saw this: That’s a rippled slab of sandstone, but with a linear groove that obliquely cross-cuts the ripple marks. Smaller, parallel grooves lie within the main groove. Here’s another look at that same one, spun around and zoomed-in: It looks as if something was dragged through the wet sand at this location, prior to its lithification. Given …
1 October 2011
Ripple marks and cross beds in the Morrison Formation
This past summer, the day after my examination of basement complex along the Colorado/Wyoming border, I drove north to Greybull, and then with Virginia Museum of Natural History paleontologist Butch Dooley to a dinosaur dig site north of Shell, Wyoming. There, in the Bighorn Basin west of the Bighorn Mountains, are dinosaur-bearing exposures of the Jurassic Morrison Formation. While Butch and his son and his two volunteers went to work …
24 September 2011
Pilot Peak: a classic horn
Along the Beartooth Highway, east of Cooke City, Montana, you will see this striking mountain: Click through to make it really big. That’s Pilot Peak. It’s a horn in Wyoming. My Rockies students get really jazzed when they see it. Glaciers carved away the rest of the mountain, leaving only this pyramidal spire. Awesome.
12 September 2011
Clinker
“Clinker” is an interesting rock type seen in Wyoming’s Powder River Basin. It forms when a coal seam catches fire, and cooks the rock above and below it, including the potential for partially melting the strata immediately above. Check out a few images of this intriguing rock here.
31 August 2011
Columns form perpendicular to cooling fronts
This morning, Dana asks about the pattern of columns in this image: She muses: If I had a time machine and surviving-fresh-lava gear, I’d head back to see what this bugger was up to. Why did some of its columns form ramrod-straight whilst others are practically horizontal, or curved? I’d imagine it was contending with some ice round the edges, maybe some water, that caused it to cool all funny. …
15 August 2011
Split concretion
Concentrically-zoned ironstone concretion in sandstone of the Morrison Formation, eastern flank of the Bighorn Mountains / western edge of the Powder River Basin, Wyoming, at the Sheridan College dinosaur fossil quarry, last week. The white stuff is caliche. A quick post to celebrate the fact that as of three hours ago, Lily & I are back home in our condo in D.C. It’s been a great summer, and I have …
Callan Bentley is Associate Professor of Geology at Piedmont Virginia Community College in Charlottesville, Virginia. He is a Fellow of the Geological Society of America. For his work on this blog, the National Association of Geoscience Teachers recognized him with the James Shea Award. He has also won the Outstanding Faculty Award from the State Council on Higher Education in Virginia, and the Biggs Award for Excellence in Geoscience Teaching from the Geoscience Education Division of the Geological Society of America. In previous years, Callan served as a contributing editor at EARTH magazine, President of the Geological Society of Washington and President the Geo2YC division of NAGT.