28 March 2014
Friday fauxld: the “Not a Box” at Confusion Hill
Posted by Callan Bentley
It’s Friday… that means it’s time for a fold. Let’s try this outcrop at “Confusion Hill” in the Franklin Mountains of West Texas:
See it? Let’s zoom in…
From the shadows to the left of the hammer, trace out the dark green layer… it may make you think of a box fold:
…but it’s not. This is actually a completely planar sedimentary bed, tilted to more or less vertical, and then cut by three differently-oriented outcrop planes:
The intersection of each (differently-oriented) outcrop plane with the (uniform) plane of the dark green bed produces a line of “apparent dip” – these apparent dips, when viewed en masse, produce an impression of a folded layer – a totally false impression.
Beware faux folds!
(And Happy Friday!)
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.
Reminds me of the classic faux fold in Titus Canyon, Death Valley.
http://mavdisk.mnsu.edu/larsop2/geog101/ConstructionalLandforms/FoldingLandforms/TitusSyncline.jpg
It used to be marked by a national park service sign referencing it as a fold, which they finally took down (hopefully because someone pointed out the error). It is pretty clearly just a perspective thing based on the two planes of erosion, as the rock wall makes a sharp turn right at the “fold”.