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20 September 2013
Friday fold: recumbent fold at Two Medicine Lake, Montana
Here’s a photo from Tom Biggs (University of Virginia), taken on the NOVA Rockies field course last summer. It shows a recumbent fold along the Front Range of Glacier National Park, in Montana, just north of Two Medicine Lake. I hope you get some ‘recumbent’ time this weekend… I know I could use some rest. Happy Friday!
13 September 2013
Friday fold: Kink band in Lodgepole Limestone, Sacagawea Peak, Bridger Range, Montana
As I’ve mentioned previously, I spent some time making GigaPans this summer out west. Here’s Lily and me on the crest of the Bridger Range, enjoying the clear skies and great geology: When this portrait was taken (by our friend Lindsay), I was shooting this GigaPan: link Try exploring it to see if you can find today’s Friday fold: a kink band in the Lodgepole Limestone (a thinly banded unit) …
30 August 2013
Friday fold: Archean BIF from Montana
My NOVA colleague Shelley Jaye brought this gorgeous banded iron formation fold back from the Archean of Montana: Gorgeous to think about what this rock represents: (1) an anoxic atmosphere, a world where iron was able to dissolve in seawater; (2) some addition of oxygen, causing the iron to precipitate out as iron oxide minerals, (3) burial to some enormous depth where rocks behave gooey-like, (4) tectonic stresses that caused …
16 August 2013
Friday fold: Sandy Hollow, Montana
Today, a view to the southwest, from close to the hinge of the main anticline in the Sandy Hollow area, a classic geological field mapping locality in southern Montana: Triassic-aged Dinwoody Formation dominates the main part of the scene. Note how the strike and dip of the positively-weathering strata wrap around. Our Rockies students mapped here this past July, trodding on hallowed ground familiar to generations of field camp students.
13 August 2013
Absaroka volcanic breccia
A lovely example of a volcanic breccia (from the Eocene Absaroka Volcanics of southern Montana) is showcased, in two different photographs.
14 July 2013
Rockies 5 concludes
My Rockies field course has wrapped up for another year – the fifth year in a row I’ve run this intermediate-level ‘regional field geology’ course in collaboration with Pete Berquist of Thomas Nelson Community College. We were fortunate to be joined by two other professional geologists this year: Chris Khourey of NOVA and Tom Biggs of the University of Virginia. It was a great group of students; no jerks among …
3 January 2013
Inside the French Thrust
Callan zooms in on the meso-scale structure of the French Thrust fault, exposed in Sun River Canyon, Montana.
12 December 2012
Fault in the Boulder Batholith
Last week, we took a closer look at the xenoliths (MME’s?) in the Boulder Batholith. Here is a look at a fracture, perhaps a small fault, in that same outcrop. There are no marker units by which we could detect offset here, so we can’t say for sure it’s a fault. But definitely weathering has been strongly enchanced along the trace of this planar feature.
6 December 2012
More xenoliths from the Boulder Batholith
The week before last, I showed you the Boulder Batholith, as it crops out southeast of Butte, Montana. Today, I’ll share a few more photos of xenoliths (or perhaps microgranular mafic enclaves?) from that same outcrop: Man, I miss that old Swiss Army knife. The damned security actors at Calgary Airport confiscated it last summer. 🙁
24 November 2012
Rock Cycle III: Igneous → Sedimentary
The Boulder Batholith outside of Butte, Montana, is actively weathering, and shedding off grus. In the third installment of the Transitions of the Rock Cycle series, we watch an igneous rock turn to sediment.
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.