At the edge of the intrusion

Mountain Beltway reader Greg Willis attended my colleague Ken Rasmussen’s Triassic Rift Valley field course last weekend, and sent me this photo of the view inside the Luck Stone diabase quarry in Centreville, Virginia:

Here’s an annotated version:

Both photos are enlargeable by clicking on them (twice).

This quarry chews into rock right along the contact between a mafic igneous intrusion and lake sediments that formed when water pooled in a low-lying continental basin that formed during the breakup of Pangea. This rift valley, the Culpeper Basin, is just one prominent basin in a whole series of Triassic grabens and half-grabens that run through the Piedmont north and south of here, including all the way to the Bay of Fundy.

A similar environment can be seen today in east Africa, where a modern rift valley hosts similar lake deposits and mafic igneous rocks:

If you were to drop maybe half a kilometer below the surface of the Afar region, you’d see a similar situation to the one that produced Greg’s quarry photo ~200 million years ago.

Visiting the Centreville quarry is by permission of the Luck Stone corporation only; the best way to see it is by signing up for Ken’s course the next time it rolls around!

A day in the field

I spent last Thursday on a long field trip in the Valley and Ridge province of northernwestern Virginia. Leading the trip was Dan Doctor of the USGS-Reston. Accompanying Dan was a UVA environmental science student named Nathan. And the NOVA crew rounded it out: professor Ken Rasmussen from the Annandale campus, associate professor Victor Zabielski from the Alexandria campus, and me. We met at the Survey at 9am, and headed west towards Strasburg, site of my Massanutten field trip.

We started off by examining three Ordovician carbonate units (all above the Knox Unconformity) on the I-81 exit ramp at Route 11. This is the same sequence seen at the classic Tumbling Run outcrop: the New Market limestone, the Lincolnshire limestone, and the overlying Edinburg Formation. We looked at fossils, stratigraphy, some minor structures, and some interesting lithified gunk on the inside of some solution cavities (small caves). Dan interpreted it as collapse breccia: lithified sediment from inside the cave. The question was: when did it form? We wrestled with the best way to test its age, and didn’t come to any clear conclusions. I love moments like that one: out in the field, one geologist shows another something that’s caught his or her attention, and the other geologist reacts, and the two toy with the idea, batting it around like a cat with an unknown object. Like the cat, geologists will either then get really excited and attack the new idea, or get bored, shrug, and walk away.

Our next stop was Crystal Caverns, a commercial cave that is in ownership limbo. Our spirited guide Babs said that it was likely the last time she would lead a tour down in the cave. She was busy liquidating the artifacts of the adjacent Stonewall Jackson Museum, which had recently been shut down by its board of directors. The cave is accessed via a small building that has been built over its mouth. It was a cool cave with a significant 3D aspect: we descended in a corkscrew like fashion, then came back up via a different route. Very cool. A shame that it is being closed (at least temporarily) to the public.

We followed the cave with lunch at a local Mexican restaurant, and while we were there, a big thunderstorm rolled through. Victor, Dan, and I played dueling iPhones to get imagery of the weather front and plot out our plan for the rest of the afternoon.

The afternoon was spent visiting outcrops on the west side of the Great Valley, working our way up to Route 50, and then west to Gore, VA. I wasn’t especially fastidious about photographing everything we saw, but here’s a sample of where I opened the camera shutter…

Ooids in the Conococheague Formation:

Same shot, zoomed in to the middle:

Fossil (blastoid? crinoid?) stem, Needmore Formation:

There were some lovely Opuntia cactus blooming among the vetch at this Needmore outcrop:

From there, we checked out the Chaneysville Member of the Mahantango Formation, where we saw some snail fossils…

…and some spiriferid brachiopod fossils:

Our last stop of the day was at the Clearville Member of the Mahantango Formation, which had lots of lovely coral fossils in it:

Dan put together a Google Map of our 17 stops; if you’re interested in checking out some of these places yourself, then this is a great resource.

I’d like to publicly thank Dan for taking a work day to contribute to our understanding. It was a lot of fun!

New “secondary structures” display at NOVA

…. And on the other side, we have secondary (tectonic) structures, focused on folds and faults:

New “primary structures” display at NOVA

One of the things I managed this week was to fill up a new display case in our Student Study area with a structural geology display. On one side is primary structures, both igneous and sedimentary….

The working life

It’s a rough life, working in the places I have to work… here are a few photos from yesterday’s field trip on the Billy Goat Trail with my NOVA Physical Geology students. Photos are courtesy Dr. Meg Coleman, who joined us for the hike.

A post-lunch lecture on river incision (note the two prominent bedrock terraces, a.k.a. “straths” in the background):

The crew climbing the dreaded “Traverse” section of the trail:

We had a nice hot day yesterday: almost 90° F! Tragically, the snack bar was closed when we got back to the visitor’s center, so we were denied our salutatory Italian ices. Back to the trail tomorrow, for the 4th of 5 trips this week…

A day in the life

This month’s Accretionary Wedge is being hosted by Ed over at Geology Happens. Ed asks the rest of us a simple question, “What are you working on now?”

Gosh, where to start? It’s a busy time for me, but then again, it almost always is.

I spent last week immersed in the NE/SE GSA section meeting in Baltimore, and on the post-meeting “Transect Trip” across the Blue Ridge and Valley & Ridge geologic provinces. After the trip, I’ve been using my blogging time to debrief the field trip with my Transect series. This is an ongoing process, but will conclude this weekend.

The week before that was nominally spring break, but for me it was really just throttling back from 1.5work to 0.6work. It was nice to breathe a bit, but I spent it prepping for my conference-induced week of absence, as well as prepping my talk for the conference.

I’ve been teaching my Physical Geology class and my Environmental Geology class at NOVA, and teaching my Structural Geology class at George Mason. This process involves constantly preparing lectures – tweaking graphics and fonts and text positioning, and making sure the sequence of graphics matches my thought-flow. I also have to prepare lab exercises, tweaking them a bit from the previous semester, correcting small errors (page numbers, etc.), and reflecting on how to improve the lab. I have an inch-thick stack of old labs with “EDITS” written on them, sitting to the left of my computer monitor. I’d love the time to deal with them all… Then there’s the grading, which is relatively painless for me except for grading exam essay questions, which takes FOREVER.

I’m also planning for this summer, recruiting students for my Rockies field class, promoting other NOVA summer course offerings (including Snowball Earth and my colleague Ken Rasmussen’s Mid-Atlantic Field Geology), reviewing applications for our third full-time geology faculty member, preparing a workshop for two-year-college geoscience faculty that we’re hosting but Heather MacDonald is planning, organizing and promoting our third annual NOVA Climate Change Symposium, finishing up with six months of work with the Honors Task Force, reading the new Appalachian mountain belt literature, revamping my website, delving deeper into structural topics I don’t totally understand, answering e-mails from ex-students, blog readers, and colleagues, organizing my lab, prepping samples (usually cutting and polishing, though also glue-reinforcing crumbly fault breccias), reviewing papers for publication, reviewing textbooks in consideration of whether I want to adopt them, writing grants, checking out new field locales, leading field trips for Sigma Xi, leading field trips for the Smithsonian, occasionally subbing as GSW meeting secretary, talking blogs with the AGU staff, advising students, planning summer travel (Turkey, I think, as well as New England), paying my bills, buying groceries, watching Battlestar Gallactica and LOST, reading my magazines, drawing cartoons for EARTH, and petting my cat.

I have also set aside some quality time for brewing and drinking beer.

So what am I working on? A lot.

Emriver in action

Today, a few photos of my spring Environmental Geology class doing a New Orleans Case Study lab using our lovely Emriver river process simulator:

That’s it. I mainly shot these photos for Steve Gough, as NOVA is participating in the new grant he submitted to NSF, but I figured I would share them here, too. The students gave permission for the use of their images. I’ll blog up the Emriver itself someday: a fun toy indeed!

Rockies course applications open

For those of you who are potential NOVA students (really, that’s pretty much anyone on the planet), I wanted to let you know that applications are now open for the July 2010 Regional Field Geology of the Northern Rockies course that I co-teach with Pete Berquist of Thomas Nelson Community College. A more detailed description is available on my website.

Contact me via e-mail if you want more information or download an application here.

To whet your appetite, here’s Rockies 2009 student Jason Von-Kundra mapping Mississippian-aged carbonates in the Bridger Range of Montana:

All that came before

Mountain Beltway is the new home for Callan Bentley’s geoblogging. NOVA Geoblog will soon be closed, but will be left untouched. Like a fossil, it will be static but present, an artifact from an earlier time. It is hoped that the thousand-plus posts accumulated there will continue to be useful to the Internet-surfing public.