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11 June 2021
Friday fold: inadvertent kink fold analogue model
It’s Friday! Adam Forte, a geology professor at LSU, posted this image yesterday on Twitter: It’s a box of sheets of newsprint, stored vertically and ignored for a while, now rotated 90° so we’re looking at a cross-sectional view. To me, this is an excellent example of a physical analogue modelling experiment (albeit inadvertent) that demonstrates the process by which kink folds form. The key parameters to get this distinctive …
7 May 2021
Friday fold: Lynchburg Group
On his way to get his COVID vaccine, Callan visits a new outcrop showing folded and faulted strata of the Neoproterozoic Lynchburg Group.
24 July 2020
Friday fold: Totier Creek phyllite
Exploring his new digs in Charlottesville, Callan is introduced to a large exposure of phyllite at a dam’s spillway. The foliation there is folded in many ways. Share in a dozen field photos of the site…
8 November 2019
Friday fold: Rist Canyon cobble
From a creek bed in northern Colorado, the Friday fold distorts foliation in early Proterozoic quartzofeldspathic gneiss, peppered with small almandine garnets.
14 June 2019
Friday fold: kinked cleavage at Harpers Ferry
Last weekend was the annual meeting of the eastern section of the National Association of Geoscience Teachers. On Friday afternoon, we visited Harpers Ferry, West Virginia, and my colleague Beth Doyle led a great field trip to examine the rocks exposed there. This was my favorite outcrop we saw: Here is a close up of this outcrop, which is framed by (anthropogenic) rock wall: Dipping shallowly from upper left to …
21 November 2018
Brittle overprinting ductile in the South Mountains metamorphic core complex, Phoenix, Arizona
Today, we take a look at the structural geology that reveals the deformation evolution (first ductile, then brittle) of the South Mountains metamorphic core complex, south of Phoenix, Arizona. Expect lots of photos of smeared-out rocks, broken by faults.
22 August 2018
Q&A, episode 5
A reader asks: “What is foliation and what makes it so important to the structure of rock?”
Callan answers with a lot of images of beautifully foliated rocks.
13 February 2018
S-C fabric in limestone, Camerino, Italy
Some scaly Italian limestone shows off two foliations (S and C) which reveal the kinematic motions that built the Apennines.
9 August 2017
A suite of new 3D models
A showcase of five new 3D digital models of awesome rock samples and outcrops, produced using Agisoft Photoscan.
21 July 2017
Friday fold: Sardinia
My friend Ander Sundell at the College of Western Idaho is the source of today’s Friday fold. It’s from somewhere in Sardinia, and I think you’ll find it visually striking: Ander says: The rocks here are Silurian phyllites generated from mudstones that were deposited on the floor of the rheic ocean basin. The color and grain size variation do an excellent job highlighting compositional layering. They were deformed during the …
Callan Bentley teaches 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.