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3 April 2012
Kink fold in Castner Marble
One more structure from the Castner Marble. This one is clearly tectonically-induced: Top to the left! (East over west)
2 April 2012
Castner Marble
The Castner Marble is an extraordinary Mesoproterozoic limestone (later re-crystallized and metamorphosed) that exhibits some primary structures (both explicit and ambiguous) and some secondary (tectonic) overprints. It’s exposed in the Franklin Mountains of west Texas.
16 February 2012
Wyler Aerial Tramway and the Franklin Mountains of West Texas
Riding a cable-car up the side of the Franklin Mountains, Callan checks out the local stratigraphy and structure (and igneous intrusions). Join him on an insightful cruise up several thousand feet and through a billion years of geologic time.
17 November 2011
Shear zone in basement complex
Callan visits a new outcrop of highly-sheared rocks in the basement complex of Virginia’s Blue Ridge province.
22 August 2011
Negative halite molds from Belt argillite
As a follow up to last week’s post about halite casts in a hand sample I collected in western Montana’s Belt Supergroup, here’s another example. Unlike those (larger) examples of halite-shaped mud cubes, this sample shows (smaller) examples of the empty space left behind by the dissolved salt crystals: Image is scanned, and the penny is to provide a sense of scale. Here we go closer up, and annotated: Not …
17 August 2011
Halite Casts from Belt argillite
I collect a lot of samples when I roam the west on my summer georoadtrips. Yesterday when I got back to my office at NOVA, I unloaded about 200 pounds of rocks from my Prius. These samples are all destined to serve as teaching aides for NOVA and GMU students in lab exercises and/or hallway displays. One of the samples I scored this summer that I am very excited to …
16 June 2011
Lawhorne Mill High Strain Zone
Callan attends a field trip in the Blue Ridge of Virginia, looking first at a Paleozoic shear zone that disrupts (and improves) Mesoproterozoic basement complex rocks.
18 February 2011
Friday fold: Jefferson River Canyon
Here’s your Friday fold, straight from the canyon of the Jefferson River, near Cardwell, Montana. Perspective is to the south. East is on the left; west is on the right. Bigger version This is right next to the outcrops of LaHood Conglomerate that I mentioned earlier this week. My Rockies course co-instructor Pete Berquist and I bring the students here for several reasons, including the conglomerate, nearby Lewis & Clark …
16 February 2011
Outcrops of the LaHood Conglomerate
Remember the LaHood Conglomerate? Here’s a few field photos of my Rockies class visiting it last July: Amphibolite clast: Marble clast: I love how well-rounded these clasts can be — like eggs. When these grains were loose cobbles, tumbling down into the Belt Sea, the Earth was only 3 to 3.5 billion years old. The rivers which carried them downhill flowed past a landscape devoid of plants and animals. Since …
31 December 2010
Friday fold: French Broad basement
The Friday fold visits the French Broad Massif of North Carolina’s Blue Ridge province.
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.