You are browsing the archive for 2014 November.
24 November 2014
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 readily in terms of sedimentary loading (compression from above), but non-bedding-parallel stylolites imply a maximum …
22 November 2014
Long week, no blog. But, hey – it’s Saturday, and I have a couple of hours of breathing room – so here are some stylolites in a crinoidal grainstrone in the New Creek member of the Helderberg Formation, exposed on Corridor H in West Virginia. Stylolites are pressure solution features, which overall form perpendicular to the maximum squeezing direction (maximum principal stress direction, σ1), and have little wiggle peaks that …
14 November 2014
Last Saturday was the Geological Society of Washington’s fall field trip. Dan Doctor, Alan Pitts, and I led a team of ~20 geologists out to the great new exposures along Corridor H in West Virginia. Here’s the team in front of some of the parasitic anticlines and synclines that decorate the larger structure of the Patterson Creek Mountain Anticline: The strata here are Silurian-aged tidal flat carbonates of the Tonoloway …
13 November 2014
Silurian aged mud cracks feature small lensoidal features: are they casts of ancient gypsum crystals?
12 November 2014
It’s been a long time since I’ve shared some of the work of our GigaPan making team. Here are some of the highlights from the last five months of work… In the images below, see if you can find (a) ten thousand fusilinid forams excavated by Texas ants, (b) Devonian trace fossils in black shale, (c) resistant beds of graywacke in a vertical orientation, (d) gastropod-rich limestone sandwiched between redbeds, …
11 November 2014
Here is the view north across the central caldera of Santorini, Greece: Click to enlarge to 9000 pixels wide This caldera formed during the Bronze Age, maybe as early as 1628 BCE or so, maybe as late as 1500 BCE. There are new volcanic islands rising in the center.
10 November 2014
What is Kenny pointing at here? Why, it’s a boulder. Where did it come from? Look uphill: This is as perfect an example of root wedging as I’ve seen! Spotted it last Friday along the C&O Canal towpath.
9 November 2014
Spotted these cross-sectioned mudcracks yesterday on Corridor H, on the GSW fall field trip: They are in the Tonoloway Formation, a batch of tidal flat carbonates with lots of evidence of shallow arid conditions.
6 November 2014
Santorini is an island with nice exposures of the Tethyan subduction complex, yes. But did you know there’s also a volcano there? 🙂 Here’s a shot of some snorkelers, with a lovely stack of pyroclastics rising up behind them. Ash, lapilli, more ash — Santorini’s volcano has been very active over the years. This is a prodigious quantity of volcanic material. In the year 1627 BCE, the eruption of Santorini’s …
4 November 2014
Good morning. Here are two images from last March’s “Border to Beltway” field trip to West Texas, on the north flanks of the Cristo Rey laccolith. Specifically, these are Cretaceous strata of the Anapra Sandstone, looking at the bedding plane of the rocks. Cutting across bedding are a series of fractures (joints) that have been highlighted by the oxidation of iron (rusting) along their edges. In the first photo, the …