16 September 2022

Friday fold: isoclinal limestone near Harrisonburg

Posted by Callan Bentley

This weekend, my family and I traveled to a little agrotainment complex north of Harrisonburg, Virginia, a joint called Back Home On The Farm. It featured a corn maze, hayrides, petting zoo, apple cider donuts, and pumpkin picking. All typical fall frolic; good clean fun.

But there were also big blocks of limestone everywhere on the property. I did my best to check them all out. I was mainly scanning for stromatolites, which occur with some regularity in the Conococheague Formation. This site was mapped as New Market + Lincolnshire + Edinburg Formations, but these blocks look most like the Conococheague to me.

No stromatolites, but I did find some nice tight folding in one block:

This is pretty intense deformation of originally planar beds, and I’m tempted to think it might be soft sediment deformation based on the massive overlying bed (which is undeformed). But it could also be a weak zone that crumpled during Alleghanian mountain building. Your thoughts?

Happy Friday to you!