Paper No. 1
Presentation Time: 9:00 AM-6:00 PM
EXTENDING THE C/S TECHNIQUE FOR DIFFERENTIATING PALEOENVIRONMENTS USING A STATISTICAL APPROACH
NADON, Gregory C., Geological Sciences, Ohio University, 316 Clippinger Lab, Athens, OH 45701, TOMESCU, Alexandru M.F., Department of Biological Sciences, Humboldt State University, 1 Harpst St, Arcata, CA 95521, PRATT, Lisa M., Department of Geological Sciences, Indiana University, 1001 East 10th Street, Bloomington, IN 47405 and ROTHWELL, Gar W., Department of Environmental and Plant Biology, Ohio University, Athens, OH 45701, nadon@ohio.edu
Two thin (0.12 and 0.46 m), laminated mudstone beds within the Bald Eagle Formation (Late Ordovician) at Conococheague Mountain in south-central Pennsylvania contain terrestrial macroflora fossils preserved as carbonaceous compressions. The limited exposure, lack of diagnostic structures, and sparse fossil evidence throughout the section, which is bracketed between the marine Reedsville Formation below and the mostly terrestrial Juniata Formation above, restricts the utility of conventional facies and sequence stratigraphic analyses for interpreting the depositional setting of the laminated mudstones. In an effort to determine the depositional environment of the fossil flora, 46 samples of mudstones were collected from throughout the 35 m thick interval, analyzed for carbon and sulfur, and the C/S values compared to those from modern depositional settings.
Statistical analyses of 1344 carbon, sulfur, and C/S values reported for six modern depositional environments (deep marine, delta, transitional (estuary/deltaic distributary channel or bay), fluvial, and lacustrine) show that most can be differentiated from one another with a confidence limit >99%. After adjusting the Conococheague C/S data for the effects of weathering and organic maturation, they were compared to modern C/S data sets using the Mann-Whitney test. Results show that the two intervals of laminated mudstones with plant fossils were deposited under lacustrine conditions, which can be easily integrated with a sequence stratigraphic model for the section. The lower fossil bed was deposited in a small lake formed as the water table rose during a regional transgression; the upper fossil bed was deposited in a small Highstand lake.
