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24 November 2010
How many structures I saw here
Yesterday, I asked for you to evaluate this rock sample of the Belt supergroup and tell me how many structures (both primary and tectonic) that you could identify in it. Thanks to everyone who participated in the discussion. Here’s my annotated copy of that photo for comparison:
23 November 2010
How many structures can you see here?
Last summer, in Bonner, Montana on my Rockies field course, I took the students to see some nice exposures of Belt Supergroup strata on the side of the road. We were keeping our eyes peeled for both primary structures (i.e., patterns in the sediment that formed at the time of their deposition) and secondary, or tectonic, structures (i.e., those that formed as a result of the rock being strained under …
28 October 2010
Accretionary Wedge #28: Deskcrops
In honor of this month’s Accretionary Wedge (geoblog carnival; this month the theme is “deskcrops”), I recorded the following short video, showcasing some samples I have in my office: stromatolite (western Montana), conglomerate (Patagonia), schist (New Hampshire), anorthosite (New York), amygdular meta-basalt (Virginia), amphibolite (California), hematite concretions (eastern Montana), and a stretched-pebble lineated meta-conglomerate (Turkey).
16 September 2010
Drilling: what, why, and how
As mentioned, I spent a significant part of last weekend was spent on a paleomagnetic sampling project with collaborators from the University of Michigan. On Friday, this was our field area: That’s the south slopes of Old Rag Mountain, a popular Blue Ridge hiking destination because unlike many Virginia peaks, when you get to the top, you see some rocks instead of 100% trees: But we didn’t come here for …
23 August 2010
Rocks of Glacier National Park
This is the second of my Rockies course student projects that I wanted to share here on the blog: it is a guest post by Filip Goc. Enjoy! -CB —————————————————————————– The Rocks around Glacier National Park, Montana: Introduction to the formations The geology around Glacier National Park is great for beginners because the area is structurally straightforward and formations are generally easy to distinguish. Still, there is a lot to …
19 August 2010
In which I am eaten by a stromatolitic Pac-Man
Let this be a lesson to you, kids. Don’t get too close to wild stromatolites, even if they are Mesoproterozoic… These exceptionally large stromatolites are on the threshold of the Grinnell Glacier, in Glacier National Park, Montana. No stromatolites or geologists were harmed during the production of this blog post. Photos by NOVA Rockies student Filip Goc.
12 June 2010
The LaHood Conglomerate
The Belt Supergroup is a series of sedimentary strata laid down in the Belt Sea, an inland sea (like modern Hudson Bay) that existed in the northwestern (by present coordinates) part of ancestral North America during the Mesoproterozoic era of geologic time. Estimates of the absolute age of these rocks range from 1470 to 1400 Ma. Mostly, it’s siltstones (argillites) and limestones, including the multicolored strata so gloriously displayed at …
26 April 2010
3,2,1, Contact!
On my structure field trip just over a week ago, we found the contact between the Mesoproterozoic-aged Blue Ridge basement complex and the overlying Neoproterozoic Catoctin flood basalts (now metamorphosed to greenstone). This nonconformity can be found just west of the Appalachian Trail at the Little Stony Man parking area in Shenandoah National Park. Here’s four photos, with my left index finger for scale, in raw and annotated versions: It’s …
22 March 2010
Transect debrief 3: Rodinian rifting
The Grenville Orogeny, responsible for Virginia’s basement complex, was one mountain-building event among many that helped put together a Mesoproterozoic supercontinent called Rodinia. But Rodinia didn’t last: it broke apart during the Neoproterozoic to form the Iapetus Ocean basin. This rifting event is recorded in Virginia’s Blue Ridge province in the Swift Run Formation and the Catoctin lava flows. It’s probably about time to start putting some of these rock …
20 March 2010
Transect debrief 1: starting in the basement
It is time to debrief the post-NE/SE-GSA field trip that I went on, affectionately dubbed the “Transect Trip” for the past 27 iPhone-uploaded “live”-geoblogged posts. First off, I’d have to say that I enjoyed the live-field-blogging experiment overall, though I’ve got some critiques of the process and products. I think it’s amazing that I can upload photos and short blog posts from my iPhone to this site with a minimum …
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.