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5 April 2012
Red Bluff Granite, and what it intruded into
Returning to his February field trip in west Texas, Callan examines the contact zone where the Red Bluff Granite intruded into a group of surficial rocks, including columnar-jointed basalt.
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.
31 March 2012
Slick!
Slickenlines (fault grooves) and fault polish on a chunk of sandstone in far western Texas.
25 February 2012
One from the UTEP Reading Room
Incipient mylonitization of a granite/granitoid, as displayed in a sample on a shelf of one of the meeting rooms adjacent to the Reading Room of the Geological Sciences building at the University of Texas at El Paso. Same side, slightly different lighting conditions: I’d call this a protomylonite. Some of you might prefer the term “augen orthogneiss.” No systematic asymmetry of the feldspar porphyroclasts is catching my eye on either …
22 February 2012
Mudcracks worth writing home about
Some sweet “columnar jointing” style mudcracks from an abandoned quarry in about the farthest west corner of Texas that you can get to, or maybe the southeasternmost corner of New Mexico. One of them, anyhow… Did you spot the imposter?
19 February 2012
Plane views
A few scenes out the left side of the airplane from when I flew from El Paso to Houston a week and a half ago… Sand dune field overprinting desert vegetation and human roadways: Outcrop pattern of horizontal strata (tracing out the contours of this hill), and the weird geometry of human road systems: More contour-hugging outcrops of horizontal strata, and a vertical joint set: Same thing: Bajada (apron of …
18 February 2012
The xenobomb
Callan shows off a new sample from Texas, a peridotite xenolith launched into the air from a maar volcanic eruption, slathered in a layer of basalt. With full intent to coin a neologism, he dubs it a “xenobomb.”
17 February 2012
Friday fold, from in front of UTEP
Another sample from the collection on display, both indoors and out, at the University of Texas at El Paso. Don’t know anything about it beyond its lovely differential weathering. Happy Friday.
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.
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.