9 December 2011

Friday fold: crumpled & faulted Brallier

Posted by Callan Bentley

There’s more than primary structures in the Devonian-aged Brallier Formation turbidites of West Virginia’s Valley & Ridge province. You can also see some cool tectonic structures there, like this syncline:

Zooming in on the axial region of this same structure:

Here’s a nice example where the compression which caused the layers to fold also triggered some faulting in more competent (stiff) layers, the coarser-grained strata of the Bouma sequence:

That’s basically an inverted, smaller-scale version of the ‘hinge collapse’ that you can see in the Greenland Friday fold featured here back in August.

Lastly, from a few feet away, take a look at the deformation here:

There’s both folding and faulting present as these strata crumpled up under the stresses of Alleghanian mountain-building. Deposited in the Devonian, these shales were deformed during the Pennsylvanian or Permian, when ancestral Africa crunched into the east coast of ancestral North America. Here’s an annotated version, highlighting the contrasting dip directions of the faults, and a central “pop-up” (or “splort“?) structure, bounded by two reverse faults of opposite orientation:

Best wishes to you and yours for a very merry weekend.