A paleontology field trip into the Upper Ordovician of Ohio

The 2013 Invertebrate Paleontology class at Wooster had its first field trip today. The weather was absolutely perfect, and the usual boatload of fossils was collected. We traveled this year to Caesar Creek State Park and worked in the emergency spillway created and maintained by the US Army Corps of Engineers for the Caesar Creek Lake dam. Exposed here are the Arnheim, Waynesville, Liberty and Whitewater Formations of the Richmondian Stage in the Cincinnatian Series of the Ordovician System. These units are enormously rich with fossils, especially brachiopods, bryozoans, trilobites, clams, snails, nautiloids, corals and crinoids. There is no better place to get students started on paleontological fieldwork, and to follow up with lab preparation, identification and interpretation throughout the semester.

The Caesar Creek Lake emergency spillway is at N 39.480069°, W 84.056832° along Clarksville Road just south of the dam. The authorities keep it clear of vegetation, and so it is an extensive exposure of bare rock and sediment. The sharp southern boundary is the rock wall shown in the top image (with the intrepid Willy Nelson and Zach Downes). Students quickly fanned out along the entire exposure, so I never did get an image of the whole class of 22 students in one place.

This is the bedding plane of a slab of micritic limestone with numerous worm burrows. Trace fossils are very abundant here. These units, in fact, have some of the first trace fossils to be specifically described in North America.

On some limestone slabs are internal and external molds of straight orthocerid nautiloids. They are often paired like this, with both facing in the same direction. This is an effect of seafloor currents that oriented the shells. The current here was flowing from the left to the right.

Many of the limestones are extremely rich in shelly fossils. Here you can see several types of brachiopods, an isotelid trilobite genal spine, and some molluscan internal molds.

I always check in here with my favorite borings: Petroxestes pera. These are bivalve incisions on a cemented seafloor (a carbonate hardground). This is the type area for this ichnogenus and ichnospecies.

Two of our sophomore paleo students, Michael Williams and Adam Silverstein, are here happily filling their sample bags with fossils. I wanted to get a photo of them in the field because they had such a geologically adventurous summer in both cool and wet Iceland and hot, dry Utah. Not many sophomores have these opportunities!

Here is another pair of nautiloids, this time showing the characteristic internal mold features of curved septal walls. Again they are nestled together and oriented because of seafloor currents.

For the rest of the semester the paleo students will be studying the fossils they collected today, each eventually constructing a paleoecological interpretation based on their identifications and growing knowledge of marine invertebrate life habits and history. Now we’re really doing paleontology!