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5 June 2014
Palimpsest tales from a Silurian limestone
My favorite rocks are those that tell multiple stories – rocks that are “palimpsest” with subsequent “chapters” of their biography capable of being teased out, based on different features to be observed in the rock. Click to enlarge What can we see in this small sample of the Silurian-aged Tonoloway limestone, from Corridor H, West Virginia? To start with, it’s sedimentary, and stratified. There are multiple layers of fine-grained gray …
15 April 2014
Bloomsburg Formation exposed near Elizabeth Furnace
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 …
22 August 2013
Natural Bridge, Virginia
Our three-day karst theme wraps up today with a visit to Natural Bridge, Virginia, an impressive sight: I went to Natural Bridge early last week to give a talk to a group of Road Scholars (an Elderhostel-like program) about the Snowball Earth. Part of my compensation for the talk was a night’s lodging at the Natural Bridge hotel, meals, and tickets to the Natural Bridge’s suite of six tourist attractions, …
7 May 2013
Brallier Formation 2: tectonic structures
Yesterday we examined primary sedimentary structures (including trace fossils) at an outcrop of Devonian-aged Brallier Formation turbidites between Deerfield and West Augusta, Virginia. Today, we’ll zoom in on the tectonic structures at the site: folds, faults, and joints. Remember, you don’t have to take my word for it. You can explore it for yourself in this M.A.G.I.C. GigaPan: link One thing that’s kind of cool about that GigaPan is the …
8 April 2013
Nice plume
Another scene from the South Page Valley Martinsburg outcrop featured here last week: a slightly mud-bedecked example of plumose structure. This plume occurs within a single graded bed (turbidite) of the Martinsburg Formation. It gets younger (paleo-up) to the right. The joint propagation that the plumose structure records began somewhere vertically above the area of this photo, and advanced downward, with the plumes spreading out as it grew. Note the …
22 March 2013
Friday fold: the case of the strangely stout stylolites
Today, we return to my field trip from last week, for a look at an odd outcrop of the Ordovician-aged Edinburg Formation: Note the car key with green lanyard, to provide a sense of scale. It’s folded, as the yellow bedding traces show in this annotated version: But what really caught my eye about this outcrop were the odd stylolites (pressure solution “seams” with a wiggly morphology and a concentration …
12 March 2013
Five new GigaPans from Thoroughfare Gap
Yesterday, I took five new GigaPans at Thoroughfare Gap, a water gap where Broad Run cuts through Bull Run Mountain, the eastern limb of the Blue Ridge Anticlinorium at my latitude. The rocks here are the Cambrian-aged Chilhowee Group, with bedding tilted moderately to the east during Alleghanian mountain-building in the late Paleozoic. To the west is the crystalline core of this massive regional fold, and to the east is …
1 March 2013
Friday fold: An odd duck
A USGS colleague shows Callan a bizarre fold outcrop in the Conococheague limestone of the Boyce quadrangle, Virginia.
20 February 2013
Crazy veins
Callan & his students visit an outcrop on the Icefields Parkway in Alberta, showing a variety of white veins cutting dark rock.
6 February 2013
Dinosaur footprints in west Texas
Everything’s bigger in Texas, even the footprints…
Callan Bentley is Associate Professor of Geology at Piedmont Virginia Community College in Charlottesville, Virginia. He is a Fellow of the Geological Society of America. For his work on this blog, the National Association of Geoscience Teachers recognized him with the James Shea Award. He has also won the Outstanding Faculty Award from the State Council on Higher Education in Virginia, and the Biggs Award for Excellence in Geoscience Teaching from the Geoscience Education Division of the Geological Society of America. In previous years, Callan served as a contributing editor at EARTH magazine, President of the Geological Society of Washington and President the Geo2YC division of NAGT.