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:
North-south trending normal faults are, well, normal and expected in the northern part of Arkansas. I reckon that they had formed as an extensional response to the Ozark Dome uplift, or perhaps to a small degree, the older Reelfoot Rift in the Mississippi River valley. East-west trending thrust faults are common in the Ouachita Mountains region, where continental collision resulted in a large compressional, orogenic event.
This begets the question: why are there north-south trending thrust faults in northern Arkansas? I have no answer to this. The geologic map of Arkansas depicts the normal and thrust faults that have significant offset, but no thrust faults are mapped in northern Arkansas. Likely because they do not have any significant offset on a state-wide scale. While these thrust faults in Marion County have an offset of less than 0.5 meters, their origin is still very curious and remains a mystery to me.