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18 May 2014
B2B 2: the mid-Atlantic phase
Folks, I’m off to lead another field course – so don’t expect much on the blog this week. This is “phase 2” of the Border to Beltway community college field exchange program. In March, over spring break, I took a dozen NOVA students to Texas to team up with a dozen students from El Paso Community College, and now it’s payback time. Our EPCC collaborators are on their way to …
9 May 2014
Friday fold: knuckling under in the Mesilla Valley shale
Here’s a fold I saw in Texas, in the Mesilla Valley shale, close to the contact with the Muleros Andesite at Cristo Rey: This is a pretty wild looking fold. Let’s zoom in on the most deformed portion: Annotation: white is top of the distinctive, blocky, buckled bed, and black is its bottom side. Red shows brittle fractures in that same bed: Looks as if it rolled over on itself …
6 May 2014
McKittrick Canyon, Guadalupe Mountains National Park, Texas
While in West Texas over spring break, the “Border to Beltway” students took a hike up McKittrick Canyon, in Guadalupe Mountains National Park. This is part of the famed Permian reef complex, the deep reservoir of Texas’s rich endowment of oil. Here, the reef comes to the surface. In fact, it pokes up a good bit into the air: Can you see it? If not, let Marcelo, Robin, and Nicole …
5 May 2014
Photoshop as a means of reconstructing fault offset
I saw this fault in Texas, north of the laccolith known as Cristo Rey: Click to enlarge I had a hard time making sense of the offset in my head, though, since the layers were of inconsistent thickness. Several people tried to convince me that the offset was “normal” (that is, right side down), but it still didn’t “click” for me in the field. So I took a photo. Back …
16 April 2014
Turitella in Buda Formation limestone
Back to Texas, today. Here’s a cross-sectioned Turitella snail from the Buda Formation limestone: It’s exposed in a block of rock on the north side of Mt. Cristo Rey. You can explore these GigaPanned blocks of the Buda in search of your own Turitella… How many can you find? link link link
10 April 2014
Fusulinids and stylolites, Hueco Formation
My colleague Joshua Villalobos shared this image with me the other day – it’s a thin section of fusulinid-bearing limestone of the (Permian aged) Hueco Formation, from the Tom Mays Unit of Franklin Mountains State Park, Texas. Click to enlarge Note the scale bar at lower left. The big fusulinid in the middle is 3mm in diameter! And that’s not even it’s longest axis! Fusulinids were big honking burrito-shaped protists …
9 April 2014
Faults disrupting the contact between the Muleros Andesite and Mesilla Valley Formation shale
Hark! What gleams on yonder contact? Well, there’s no glaciers to polish anything ’round these here parts (southernmost New Mexico + westernmost Texas), so I reckon it must be fault polish. Let’s test that hypothesis by looking for slickensides… Sure enough! There they are! Unlike the deformation we saw yesterday, this faulting of the contact between the Muleros Andesite (Eocene) and the Mesilla Valley Formation shale (Cretaceous) into which it …
8 April 2014
Deformation associated with the intrusion of the Muleros Andesite
Yesterday, I showed off a few views of the contact between the Cretaceous aged Mesilla Valley Formation shale and the hypabyssal Muleros Andesite which intruded into it during the Eocene at Mt. Cristo Rey (on the US/Mexico border where Texas meets New Mexico). Today, I’d like to look at some of the structure associated with the contact zone. First off, take a look at this image, which is looking orthogonal …
7 April 2014
Contact between Muleros Andesite and Mesilla Valley Formation shale at Mt. Cristo Rey
There are two rock units in this photo. One is igneous, one is sedimentary. Can you find the contact between them? It’s somewhere along this dashed line… The Mesilla Valley Formation is Cretaceous shale with some sandstone. The Muleros Andesite (pretty much identical to the Campus Andesite you find at UTEP) is Eocene. Here’s a closer, more precisely-constrained, look at it: …but that one is in the shade. It’s bolder …
3 April 2014
Cribratina, an index fossil for the Albian age
These four slabs, collected at “Fossil Hill,” north of the Cristo Rey laccolith at the Chihuahua (Mexico) / Texas / New Mexico triple point, bear positively-weathering fossils of the benthic foraminiferid called Cribratina, an index fossil for the Albian age / stage: My field notebook serves as an imperfect sense of scale. Here’s the Albian in the context of the middle of the Cretaceous period of geologic time, from the …
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.