EVIDENCE OF ORBITAL FORCING UPON THE MISSISSIPPIAN VINTON MEMBER OF THE LOGAN FORMATION, OHIO

There is considerable debate in the literature regarding the roles of tectonic versus orbital forcing as controls on the sedimentary cycles preserved in shallow marine sediment deposited during the Mississippian. The purpose of this study is to place constraints on the processes controlling the lithologic layering within the Logan Formation. The Logan Formation is Mississippian in age and found throughout central Ohio. The lithology consists of varying layers of mudstones and sandstones. We assume that if the major processes controlling sedimentation are tectonic the rates of deposition are rapid and sporadic, while with orbital forcing the rates would be uniform. Diffuse spectral data was collected with the use of a Minolta CM2600D UV/VIS Spectrophotometer at a 2-centimeter resolution over 45 feet of core. With the use of statistical methods such as Principle Component Analysis and Time Series Analysis, major factors influencing sedimentation can be extracted and examined for their significance. By creating a spectral signature of major influencing factors, we can match mineral spectral signatures and infer processes of deposition and therefore create a potential depositional environment. Wavelet analysis allows for graphical representation of periodicities, which can then be matched to Milankovitch orbital cycles. Sedimentation rates are inferred by matching orbital cycles to periodicities within the rock record. The rates found in this study were found to be consistent, with a range of 3.0 – 3.8 cm/ka. The Milankovitch cycles that were found to have influenced every variable were the short eccentricity and obliquity cycles at 112ka and 34ka, respectively. Only two factors out of eight were able express the precessional cycle at 17ka and 21ka. It must be noted that these cycle lengths are specific to Carboniferous time because the duration of the Milankovitch cycles are known to change over geologic time. Our results were found to be consistent with a study done by Miller and Erickson (1999) where marine cyclothems can be constrained by Milankovitch orbital cycles.