|
||||
|
||||
|
Introduction to the Project The Upper Ordovician rocks in the tri-state area around Cincinnati are among the most fossiliferous in the world. They contain extraordinary numbers of exquisitely-preserved brachiopods, bryozoans, corals, echinoderms, trilobites, clams, snails, cephalopods, and numerous other smaller groups, some known only from this area. Cincinnatian fossils are displayed in virtually every natural history museum in the world, and the rocks which contain them are now internationally-recognized type sections. The Cincinnatian is also one of the best examples of a calcite sea depositional system. Despite having been studied for over 150 years, though, Cincinnatian rocks and fossils still hold fundamental paleontological and sedimentological mysteries, and every year new discoveries are made. In the past few years the Upper Ordovician of the Cincinnati area has been the scene of a revolution in our concepts of Paleozoic communities and environments, fueled primarily by new techniques and ideas in paleobiology, sedimentology and the chronostratigraphic wonders of sequence stratigraphy. This region, with its remarkable fossils and exposures, is the focus of a Keck Geology project in which students are investigating fossils and sediments in the context of changing paradigms in historical geology and paleontology. Upper Ordovician rocks are exposed in a broad, gentle structural arch with its axis passing through Cincinnati. The most useful outcrops are roadcuts and creek banks beginning in the north near Richmond, Indiana, and Dayton, Ohio, and extending south across the Ohio River into the northern counties of Kentucky. Rock types are predominantly claystones and grain-supported limestones deposited on shallow marine ramps, typically between normal and storm wavebases. The carbonates are formed primarily of biogenic debris, with considerable early calcite cement precipitated from seawater and dissolving aragonite shells under calcite sea geochemical conditions (Palmer et al., 1988). The shales are formed of clay-rich sediments eroded from mountains formed during the Taconic Orogeny to the east. Sedimentary structures include common shallow-water features, including ripples, soft-sediment deformation, hardgrounds, imbricated fossils, and tempestites. Recent stratigraphic work by Holland (1993) and U-Pb zircon dating (Tucker and McKerrow, 1995) places the Cincinnatian within a second-order supersequence (the "Taconic") at approximately 454 to 443 Ma. Holland et al. (1997) and Miller et al. (1997) have established a hypothetical framework of storm cycles for the Cincinnatian, and Pope et al. (1997) have convincing sedimentological and stratigraphic evidence of seismites throughout the units derived from earthquakes along the Taconic front and the Cincinnati Arch. |
||||
|
||||
|
Individual project descriptions and images can be seen by clicking on the student names at the top of this page. Two projects are sedimentological in scope: Bryn Clark is studying an extraordinary interval of soft-sediment deformation, mostly large ball-and-pillow structures, in the Fairview Formation in northern Kentucky which may be associated with seismicity during the Cincinnatian (see Pope et al., 1997). Matt Howard made over 100 thin-sections of shelly limestones in several sections of the Grant Lake Formation in northern Kentucky. He hypothesizes that these shell beds and their associated sediments were formed primarily by large storms. Two projects are concerned with hardgrounds (synsedimentarily cemented seafloors; see Wilson & Palmer, 1992, and Palmer et al., 1988) and their fossil faunas: Dana Dettmers is examining a hardground in the Grant Lake Formation of northern Kentucky which hosts a bryozoan mound on its top surface, and bryozoans hanging underneath as part of a cave fauna. It also has large borings penetrating the hardgrounds and the bryozoans. Mike Vanden Berg found an excellent hardground with rare edrioasteroids and large bryozoans. He is working to place this hardground in a stratigraphic, sedimentologic and paleoecologic context. The remaining three projects are mostly paleontological, with considerable sedimentology included: Laura Ward collected over 100 solitary rugose corals and is mapping and quantifying their borings and encrusting bryozoans to support a "reclining" model for the coral life position. Jesse Lazzuri is studying the ubiquitous borings in calcareous substrates in the Cincinnatian. She has already found some undescribed types, along with interesting "pseudoborings" formed when the bryozoan host grew up and around some sort of soft-bodied encruster. Woody Fischer's project as an assessment and analysis of the diverse bioimmured fauna (fossils formed by being molded in the skeletal walls of others; see Wilson et al., 1994, for examples in the Cincinnatian). Woody is also taking advantage of the bioimmurations to examine ecological successions on aragonite shell substrates. Since all of the Cincinnatian outcrops are within a 3-6 hour drive from Wooster, we took several three- and four-day trips from Wooster to complete our fieldwork, staying in inexpensive motels. The rest of our time we were based in Wooster, where we used campus housing and food services while working in the geological laboratories and libraries. In the Wooster labs we used thin-sectioning equipment, petrographic and dissecting microscopes, fossil preparation tools, and numerous computers to do our work. We also visited the libraries and geological facilities at Ohio State University (hosted by Scott Bair, chair of the department) and the Cincinnati Museum of Natural History (with Colin Sumrall, curator of the invertebrate fossil collection). For recreation we visited Big Bone Lick State Park in Kentucky (which has marvelous Pleistocene fossils), Serpent Mound in southern Ohio (an archaeological site), the Cleveland Museum of Natural History (where we had a fascinating tour of the paleoanthropological facilities from Bruce Latimer), the Cleveland Museum of Art, and the Cleveland Botanical Gardens. While this all sounds terribly serious, we had a great time on the Keck Ohio project! |
||||
|
||||
|
|
