You are browsing the archive for April 2014 - Page 2 of 2 - Mountain Beltway.
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 …
6 April 2014
Structural geology of Mount Evan-Thomas
Longtime reader and frequent contributor Howard Allen has three images to share with us today. Let’s see what he’s got… Oh my. What is that? West ridge of Mount Evan-Thomas, Opal Range, Peter Lougheed Provincial Park, Alberta. View looking south across Grizzly Creek at structural features (yellow boxes outline detail images to highlight key features, shown in subsequent images). Rocks are Carboniferous (Mississippian) carbonates. Location is 50.7660, -115.1259. Photo taken …
4 April 2014
Friday fold: ‘Ben Folds One’
We have a guest Friday fold today, from reader Ben Mackay-Scollay of the Monash University School of Geosciences in Melbourne: Ben writes: Hey there Professor Bentley, been a fan of your blog for a while and I thought you might be able to use this for your Friday Fold series. It’s an upright fold at Bermagui in New South Wales, where I visited recently as part of my post-grad coursework …
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 …
2 April 2014
The wonder of cracking open a xenobomb
On “Border to Beltway”‘s visit to Kilbourne Hole, after we whet our appetite with Hunt’s Hole, Michael finds a xenobomb. Ernie and Boris look on with envy: A “xenobomb” is a xenolith (in this case, of mantle peridotite), slathered in a coating of lava and tossed out of a volcano in the middle of a liquid droplet (a bomb). Here’s what they look like in cross-section: You can experience some …
1 April 2014
Lost in My Own Backyard, by Tim Cahill
On Saturday of this past weekend, I led a field trip to Sideling Hill and Paw Paw Tunnel, and on the (1.5+.75+1.5=) 3.75 total hours of driving, I listened to the audio book version of Tim Cahill’s short book on traveling around in Yellowstone National Park. It’s a fun little book, but I wished it was longer. I was able to consume the whole book in a single day’s driving. …
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.