20 March 2015

Friday fold: flexed turbidites

Posted by Callan Bentley

Spring is almost here! As you get ready for the equinox, enjoy this gentle fold on a Friday:


These are turbidites (graywacke and shale) of the late Ordovician Martinsburg Formation, seen in Edinburg Gap, western Massanutten Range, greater Shenandoah Valley, Virginia.

Bedding is flexed very slightly here, from moderately-dipping to more steep, and then back to moderate again. Slickensides on the top of some exposed layers indicate the beds shifted slightly relative to their upstairs and downstairs neighbors: an example of folding through flexural slip. Cleavage here dips to the left, at a steeper angle than bedding.

Happy Friday, and happy Vernal Equinox!