PALEOENVIROMENTAL INTERPRETATIONS OF A LATE PENNSYLVANIAN ESTURINE SETTING (BONNER SPRINGS SHALE; KANSAS CITY GROUP).

*Edinger, P.V., J.C. Gleason, S.A. Hageman, O.L. Hull, J.R. Martin, M.W. Price, and B.W. Skelton
Department of Natural and Physical Sciences, Park University.

The depositional environment of the Bonner Springs Shale Member at Park University’s Parkville campus displays characteristics of a tidally influenced deltaic environment. The rapid deposition of vertically laminated shale exhibits distinctive periodicities in lamina thickness that ranges on the order of a few mm to a few cm. These predictable variations in thickness occur vertically in the bed and reveal direct evidence of daily high and low tides. The thicknesses of these lamina couplets gradually increase to their maximum thickness during spring tides and gradually decrease to their minimum thickness during neap tides. The taphonomy of the extremely abundant and extraordinarily well preserved plant fossils indicates rapid rates of sedimentation in a relatively protected bay with low tidal ranges (micro-tidal< 2m). Large salinity fluctuations inhibit water-body mixing in the Late Pennsylvanian Midcontinent Seaway, causing stratification of sediments marked by occasional thick, coarse sandstone lenses. These coarse sandstone lenses indicate periodic flooding of the bay’s fluvial source. Evidence of a transitioning estuarine environment is further supported by the lack of fossilized marine fauna coupled with the rare presence of trace fossils and insect wings. Further studies will discover the role of fluctuating water depths and salinity in the stratification of sediments. Trend changes in sediment types, sizes, and depositional geometries will further delineate the variability in this transitional environment of deposition.