TESTING PALEOENVIRONMENTAL GRADIENTS IN THE UPPER ORDOVICIAN WHITEWATER FORMATION OF THE CENTRAL UNITED STATES

Limestones of the western and eastern flanks of the Cincinnati Arch (CA) were, at the time of deposition, a continuous intracratonic basin that received sediments from the Taconic Mountains in the east. Although separated by the CA today, these rocks are roughly correlated on the basis of macrofaunal associations. Previous studies based largely on lithostratigraphy have suggested that the primary difference between the eastern and western flanks of the CA was water depth, such that shallower water, higher energy conditions existed in the east near Maysville, KY. Likewise, deeper water and lower energy conditions existed on the western flank of the CA near Camden, OH. The warm water faunas of this region are at times punctuated by coral-dominated epibole horizons. Grewingkia canadensis is the most abundant rugose coral in these horizons and it is useful for correlating these once-continuous strata.

The focus of this study is to investigate roughly coeval strata to test previous paleoenvironmental interpretations using the preservational style and ecophenotypic variation observed in individual corals collected from localities on either side of the CA. For this study, samples of the solitary rugose coral G. canadensis were collected from near Camden, OH and Maysville, KY. Encrusting epizoans and macroborings such as Trypanites sp. are present on most coral specimens found in the Whitewater Formation. For each sample set, the average amount of boring and epizoan coverage was established as a proxy for bottom dwelling time and an average taphonomic score was also calculated based on corallum preservation.

It is possible to use differences in epizoan type, average coverage and corallum preservation (amount of abrasion) from these disparate localities, as well as coral size (a function of age and ecophenotypic variation) to make paleoenvironmental inferences about each locality. The two localities show distinct differences in rates of epizoan and boring coverage. These data were used to determine relative energy for the two localities which was used to test paleoenvironmental inferences such as water depth, relative sedimentation rates, relative light penetration, and related factors.