Bearded Geology

People looking at folds. Faces obscured to protect identities. ¡Mas folding!. Action shot of man pointing at a fold Normal fault in sandstones and shales Recently, I got to join a field trip to the Ouachita Mountains to discuss a spectacular structural event that took place in the Late Paleozoic. The strata of the Ouachita Mountains are dominantly sandstone and shale beds from the Cambrian to the Pennsylvanian that were deposited in an offshore, deep water environment somewhat similar to the deep water regime of the Gulf of Mexico. Beginning in the Mississippian Subperiod, a compressional event initiated as proto-North America collided with a small land mass (volcanic arc) to the south creating the Ouachita Mountains, a...

While between rain storms earlier this week, I was able to get out into the field to do some outcrop work near Yellville, Marion County, Arkansas. I visited a roadcut near the US Hwy 412/AR Hwy 125 junction that is made of Lower Ordovician age  dolostone rock with some shale intervals. Interestingly, it has a couple thrust (reverse) faults on display: Thrust fault through carbonate rock (Facing north. Scale: 1.5 m staff with 10 cm intervals) A closer look at the fault in the lower-right corner of the previous image An even closer look at the fault. Lots of fault gouge. Notice the clasts that have rotated. Another thrust fault at the same roadcut (Facing north. Scale: 1.5 m staff) Some weeks ago, I was visiting a roadcut near Cotter, Arkansas  where I left with buckets of samples to analyze. One such sample was a large cobble that I slabbed on the rock saw and found these beautiful normal faults, with a baby graben flanked by two horsts: Faulte...