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!
Interesting looking formation. But how likely is it that Conococheague (575M yrs old) would be comingled in a field of Ordovician formations (475 M yrs old)?
The top of the formation sort of looks like Edinburg (on the left) and New Market ( “dove gray” on the right)
We have this limestone EVERYWHERE in Rockingham County. In fact, further south on that road is a field that has apparently never been cleared because it is FULL of boulders, the road goes right through and they are on both sides. Rockingham County is FULL of limestone, and there is a lot of Radon in homes as a result. I’ve seen all sorts of formations all throughout the area in different limestone rocks. You should drive up 33 West to West Virginia where you can see the layers/striations of the rock there. It’s pretty cool, especially once you cross into West VA.
Fair points! 🙂