Looking at Ordovician carbonates in Germany Valley, West Virginia, a few weeks ago on Rick Diecchio’s GMU sedimentology and stratigraphy course field trip: Lots and lots of brachiopods… Crinoid columnals mized with brachiopods: A set of coarsely-infilled trace fossils: Crinoid stem: Nice strophomenid brachiopod: Bryozoan? Receptaculid?
A virtual field trip to a quarry in far western Virginia, showing anomalous igneous intrusions (a dike and a sill) of Eocene age cross-cutting early Paleozoic carbonates.
Spring is almost here! As you get ready for the equinox, enjoy this gentle fold on a Friday: These are turbidites (graywacke and shale) of the late Ordovician Martinsburg Formation, seen in Edinburg Gap, western Massanutten Range, greater Shenandoah Valley, Virginia. Bedding is flexed very slightly here, from moderately-dipping to more steep, and then back … Read more
Here’s a little scene along Route 340 / 522, north of Front Royal and south of Double Tollgate, Virginia, in the Shenandoah Valley: The rock here is limestone and shale of the Edinburg Formation, a late Ordovician unit that records the transition from passive margin sedimentation to the increasingly ‘dirty’ clastic influence of the Taconian … Read more
Here’s a sweet little sample of migmatite (~470 Ma late Ordovician Taconian Orogeny, U/Pb date from zircon), that my students and I spotted last week on the Billy Goat Trail, downstream of Great Falls in Maryland’s metamorphic Piedmont province: Note the white translucent quartz, the orangey (partially kaolinitized and rusty stained) opaque potassium feldspar, and … Read more
Today, I initiate a series of posts based on some of the geology I saw over spring break, in west Texas and southern New Mexico, on the field exchange between Northern Virginia Community College and El Paso Community College that I helped facilitate. We spent our first morning in the field in the Franklin Mountains, … Read more
Callan and his family visit a Virginia winery that features tasty libations and chunky nautiloid fossils, both products of the same local geology…
Following a tip from a colleague, Callan finds a rich trove of fossil graptolites in Ordovician shales exposed at Mint Spring, Virginia.
Following on yesterday’s post about the kink bands within the strained metagraywacke of the Laurel Formation in DC, let’s take the opportunity today to go to Klingle Valley, site of a different facies within the Laurel Formation: a strained metaconglomerate. Though the exposure isn’t as great as the Purgatory Conglomerate, I think you’ll find plenty … Read more
Last week before GSW, I spent several pollen-choked hours in Rock Creek Park, GigaPanning some of the rocks of the Rock Creek Shear Zone. Here are some exposures in the bed of Broad Branch that show lovely kink banding. In at least one spot, you can see a conjugate pair, so these rocks were (1) … Read more