Unexpected Findings

In geology class we went on a required river rafting trip which lasted three days and two nights. At night we set up camp on a beach or sandbar. After setting camp for the second night, we decided to take a hike up a wash near our camp. We found lots of wild flowers and a variety of rocks, some with crystals, others brown and bland, but mostly chert and limestone. While hunting for interesting rocks, the advisor that was with us found a rock that we later found out contained a mineral called glauconite. Mrs. Faatz was very excited to see this and told us that this rock is glauconitic sandstone from the Lodore Formation. Glauconite is a clay that forms in shallow marine conditions. It is "typically found as rounded aggregates or 'pellets' of very fine grained scaly particles, having a blue-green to yellow-green color" (http://www.mindat.org/)

After seeing the glauconite and other interesting rocks, Mrs. Faatz decided she wanted to hike back up there and see what she could find. While up there for the second time, we made the discovery. Amanda saw a boulder that she wanted to test to find out what it was. Right before putting acid on it she realized that there were fossils that looked like clam and snail shells. They weren't what we thought though. These fossils were brachiopods and crinoids. Relative dating using the fossils allows us to say this rock is Mississippian in age (about 350 million years ago). These animals lived shallow tropical seas. This limestone is part of the Madison Formation and was found in the wash because it had been eroded from the cliffs above us. After the brachiopods and crinoids died, sediment slowly started to build up and eventually enough sediment was deposited over them to compress them into the boulder that we saw. Although we didn't plan on finding fossils on this trip, it was fun, interesting, and fit for a geology trip.