Here’s a picture of me on an outcrop of rock:
Before I explain what I’m pointing to, I thought I’d provide some context. It was Saturday morning in late September and I was on a field trip for a seminar course I’m taking this semester called “Collisional Orogenesis”. The class covers the processes involved in the evolution of mountains that form when continents collide.
We ventured out to the Tennessee and North Carolina part of Appalachian mountains to gain a field-based perspective. This area was chosen since it is the closest mountain belt that formed in this way and there are some pretty fantastic rocks. We were having a good time driving around, looking at rocks, and camping in truly beautiful places. At this outcrop, some students were unlucky enough to come in contact with stinging nettle while bushwhacking up the hillside. Don’t let that be you!
Maybe you can tell the lower rock I’m standing on differs from the darker rock above my waist. The lower rock is a sandstone and the upper rock is a shale. The sediments that make up these rocks were deposited about 600 million years ago when an ocean basin was forming during continental rifting.
After that, the continents collided resulting in the formation of Pangaea. This generated tectonic stresses that were so great these rocks became deformed. The sandstone (lower rock type) is relatively strong so most of that deformation was taken up by the weak shale layer (upper rock type). We can get a sense of direction of motion because there was a quartz pod in the shale (white blob I’m pointing to) that was rotated as the bounding layers moved past each other. Lucky us!
Not so lucky is being attacked by yellowjackets on the way back to the vans… It’s all part of the job though, I guess.