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.

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Transect debrief 6: folding and faulting

Okay; we are nearing the end of our Transect saga. During the late Paleozoic, mountain building began anew, and deformed all the rocks we’ve mentioned so far. This final phase of Appalachian mountain-building is the Alleghanian Orogeny. It was caused by the collision of ancestral North America with the leading edge of Gondwana. At the latitude of Virginia, that means northwestern Africa (Morocco and/or Mauritania).

Whereas the first two pulses of Appalachian mountain building were relatively provincial affairs, this Alleghanian phase was a full-on continent-on-continent smackdown. The Himalaya (India colliding with Eurasia) would be a good modern analogue for the Pennsylvanian and Mississippian Appalachians.

When I was live-blogging the trip, I posted this photo of Judy Gap:

It was a bit hard to get it all into one measly iPhone frame (hence the tilted angle: those trees are in fact vertical!), but what you’re looking at here is the erosion-resistant Tuscarora Sandstone (Silurian in age; quartz-rich beach deposits) that outcrop as a ridge. However, here at Judy Gap, there are two ridges. What gives? This is where I was introduced to a new term that is apparently becoming a common phrase in the structural geology literature: contraction fault.

The story most Physical Geology students get about fault types is that tectonic extension causes normal faults, while tectonic compression causes reverse faults. Contraction faults are faults that display an apparent “normal” sense of motion, but were caused by a compressional tectonic regime. How the heck does that work, you may ask? Consider the following diagram:

So the deal with contraction folds is that they might start out “reverse” but are then rotated and tipped over as deformation proceeds. The former footwall becomes the new “hanging wall,” and the sense of motion is obscured by this new orientation. This means that they do represent contractional strain, but a freshman geology student is unlikely to spot it at first glance.

The Germany Valley to the east of Judy Gap is a big breached plunging anticline, as I attempted to show with this iPhone photo from the Germany Valley Overlook along Route 33:

It’s a bit easier to see if you jump up in the air 10 kilometers or so. Fortunately, that’s precisely why God created Google Earth:

The valley is hemmed in by a big V-shaped fence of mountains, all held up by the Tuscarora. It’s tough stuff. During Alleghanian folding, the crest of the anticline was breached, and water was able to get inside and gut the weaker rocks. The quarry annotated in the photo is mining the same Cambrian and Ordovician carbonates seen in the Shenandoah Valley back in Virginia (Lincolnshire and Edinburg Formation equivalents). A pattern geologists have noted with eroded anticlines is that older rocks are exposed in the middle of the structure, with younger rocks flanking them along the sides.

So that’s a glimpse of the big picture of deformation in the Valley & Ridge, but we can also see cool deformation at smaller scales… Stay tuned…