Another gem from Saturday’s Historical Geology field trip: the bottom of a fine sandstone bed in the Devonian Brallier Formation, showing a variety of primary sedimentary structures, including tool marks, trace fossils, and several flute casts. Current flow direction here would have been from upper left toward lower right. Here’s a version of the photo … Read more
On Saturday, I took my historical geology class on their field trip out to Corridor H, West Virginia. We made a stop at the Mahantango Formation outcrop exposed on the eastbound exit ramp near Baker, and poked around there for fossils. These Devonian-aged siltstones are chock full of invertebrates including rugose corals, crinoids, articulate brachiopods, … Read more
Here are a few shots of a Devonian aged reef exposed in Mustoe, Virginia – one of the sites I visited this spring with GMU’s Rick Diecchio, when he led his sedimentology and stratigraphy trip there. At first, the outcrop made no sense to me – I kept searching for bedding, and failed to find … Read more
Another site from the GMU sedimentology field trip in April: An outcrop on Route 33 in Brandywine, West Virginia, showing the Millboro Formation. It’s mostly shale, with some intriguing sandstones, too. There are fossils and diagenetic carbonate nodules (concretions). Here’s the outcrop, the largest GigaPan I’ve taken so far (7.9 billion pixels): link The shale … Read more
Last one in the triumverate sent in by reader Eric Fulmer: Annotated: Happy Friday and (for many of you) happy end of the semester!!
The Friday fold shows clastic detritus (turbidites or “flysch” from the Acadian Orogeny) crumpled into tight folds due to the later Alleghanian Orogeny.
Recently, I posted about an excellent road cut in Fort Valley showing well-developed 10 cm+ Zoophycos trace fossils. Presented here are three new GigaPan images (two outcrop; one macro) of Zoophycos from the Devonian-aged Mahantango Formation: link link link These images are part of a new “virtual field trip” that I organized to supplement my … Read more
A morning’s field trip yields an outcrop of excellent Zoophycos trace fossils in southern Fort Valley, Virginia.
Saturday I posted some images of bedding-parallel stylolites from one member of the Devonian-aged Helderberg Formation (or one formation in the Helderberg Group; I’m not sure whose stratigraphy is preferable in this case). Here we are, further up-section, and you can see both bedding-parallel and non-bedding-parallel stylolites overprinting the limestone: Bedding-parallel stylolites can be understood … Read more
Here are some rugose coral fossils (along with some cross-sectioned articulate brachiopod shells) to be seen in the Clearville member (~80 feet thick) of the Mahantango Formation, exposed on the north side of route 55, just west of the West Virginia / Virginia border. These fossils are cool in their own right (what fossils aren’t?) … Read more
Here’s a breccia that Dan Doctor and I found in a tabular zone within the Helderberg Group (Devonian limestones) in one of the massive new roadcuts along Corridor H. link Is it a fault breccia or a sedimentary breccia? The breccia was bedding parallel, which suggests it could be just another bed, but it’s so … Read more
Some folds this week from coastal exposures in western Boothbay Harbor, Maine, where I’m on vacation for one more day… Acadian metamorphics (schist, gneiss), with injected granite pegmatite that has also been folded (and boudinaged): Happy Friday!
Okay, I photoshopped that one up. This one too… Here are the originals… And, if you’re a scale-off-to-the-side-of-your-main-subject purist, here’s a different shot of this quintessential boudin: And, while we’re at it, here are some other fine boudins (of granite pegmatite) exposed along the coast of West Boothbay Harbor, Maine: Some nice coastal ecology to … Read more
Pemaquid Point, Maine, is a locally-owned and -managed park near an old lighthouse. I went there yesterday with my family. We’re on vacation in coastal Maine for a week. At Pemaquid Point, the action of waves have cleaned the rocks, and they offer a delightful three-dimensional look at Acadian-aged metamorphics and granite pegmatite dikes, with … Read more
Click to enlarge You owe it to yourself to click through and make this bigger. Check out the prominent lower left to upper right thrust fault, and the shattering in the shorter limb of the underlying syncline. Is that another one to the right? Happy exploring, and happy Friday!
While on Corridor H last week with Team “Border to Beltway” (and USGS research geologist Dan Doctor), we stopped at the putative mass transport deposit. We still haven’t figured out which unit this is (It’s not the Foreknobs), but as we approached it, Dan wondered aloud, “I wonder where the top of the Devonian is. … Read more
As with last week, the Friday fold comes from my Field Studies in Geology class to Sideling Hill and the Paw Paw Tunnel. This is a view of the downstream (north) entrance to the Tunnel, with students highlighting the trace of bedding in the turbidites of the Brallier Formation: Can’t make it all out? Let’s … Read more
Where the Needmore Formation is falling apart on Corridor H, sloughed-off shale is piling up in a tiny talus slope: You could slap a protractor on that photo and get a pretty good measurement of the angle of repose of this chippy, flaky granular material. Eyeballing it, that looks like about 45° to me.
The Wallbridge Unconformity is a surface of stratigraphic hiatus or erosion between the depositional influence of the Tippecanoe and Kaskaskia epeiric seas. After Alan Pitts and I located ourselves in the Oriskany Sandstone (terminal Tippecanoe stratum), we looked stratigraphically above the quartz sandstone for the overlying unit, which should be the Needmore Formation shale (beginning … Read more
Today, a few more photos from the field trip last month to Corridor H, the fine new superhighway with so little traffic out in eastern West Virginia. Our antepenultimate stop of the day was at an outcrop we inferred should hold the Oriskany Sandstone, a Devonian quartz arenite that lies stratigraphically above the Helderberg Group … Read more