You are browsing the archive for 2014 April.
30 April 2014
Ooids are fish-roe-shaped-and-sized spherules that result from the chemical precipitation of calcite from supersaturated water. Here are a few nice examples from Monday’s field trip.
29 April 2014
Remember this past winter when Alan Pitts and I found what we interpreted to be a mass transport deposit (a submarine landslide/slump) along the new section of Corridor H leading up the Allegheny front? Well, I was back out there yesterday, with Dan Doctor (USGS Reston) and Jay Kaufman (University of Maryland). One new thing we found was lots of weathered-out “ploudins” (pillows/boudins), many of which had a “sleigh” shape …
25 April 2014
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 try zooming in, and laying on some annotation: Happy Friday!
18 April 2014
Here’s what the Sideling Hill road cut looked like last month: It’s a terrific example of a syncline. Usually I show folds in profile view, but here, the view is essentially perpendicular (not parallel) to the axis of the fold: Sideling Hill’s rocks are early Mississippian in age, made of debris shed off the late Devonian Acadian Orogeny, and they were folded during Alleghanian deformation in the Pennsylvanian-Permian.
17 April 2014
I found this interesting looking slab of gray limestone last summer in the Bridger Range of Montana, in one of the talus slopes on the north side of Sacagawea Cirque. The high-contrast pattern reminded me of something, but I couldn’t say quite what. Then I realized: it looks like one of those indigenous pictographs, where the artist puts their hand up to the rock and spits paint all over it, …
16 April 2014
Back to Texas, today. Here’s a cross-sectioned Turitella snail from the Buda Formation limestone: It’s exposed in a block of rock on the north side of Mt. Cristo Rey. You can explore these GigaPanned blocks of the Buda in search of your own Turitella… How many can you find? link link link
15 April 2014
As noted previously, I live in a regional scale fold: the differential erosion of the Massanutten Synclinorium has produced the ridge of Massanutten Mountain, which separates the Fort Valley from the Shenandoah and Page valleys on either side. The Fort is “fort” like because the strata which underlie it are relatively friable, soluble, or otherwise erode-able. The ridge-forming layer is the Massanutten Sandstone, a Silurian-aged quartz arenite. Here’s a boulder …
14 April 2014
A sure sign of the advent of spring in Fort Valley is the blooming of the shadblow, an understory tree species with clusters of white flowers: My wife and I took our son for a hike yesterday, and the shadblow was pretty much the only tree with anything on its branches: I infer that shadblow is named for the fact that its flowers “blow” (bloom) when the shad swim upstream …
11 April 2014
My student James O’Brien took this image of a kink band along the Billy Goat Trail, downstream of Great Falls in Maryland’s metamorphic Piedmont province. A lovely little structure, don’t you think? Thanks, James! Happy Friday, all.
10 April 2014
My colleague Joshua Villalobos shared this image with me the other day – it’s a thin section of fusulinid-bearing limestone of the (Permian aged) Hueco Formation, from the Tom Mays Unit of Franklin Mountains State Park, Texas. Click to enlarge Note the scale bar at lower left. The big fusulinid in the middle is 3mm in diameter! And that’s not even it’s longest axis! Fusulinids were big honking burrito-shaped protists …