Sedimentology, Geochemistry and Paleobiology of a Marginal Marine Depositional Environment, the Mansfield Formation, Martin County, Indiana

Abstract

The Mansfield Formation of southwestern Indiana is comprised of varying sequences of mudstones, sandstones, shales, limestones and coals that date from the Pennsylvanian. Two outcrops in Martin County, Indiana, contain bedded and cross-bedded sandstones and laminated and friable siltstones, with a coal seam in one outcrop. Scouring, ripples and clay drapes are common in both outcrops. Carbon and sulfur analysis reveals total sulfur values consistently below 0.1wt.% and widely fluctuating C/S ratios. Trace fossils include Sclarituba isp., Treptichnus isp., Haplichnus isp., Skolithos isp. and tetrapod tracks. Roots and other plant material are common in some units. Palynological analyses of coal samples place the stratigraphically higher of the two outcrops to a position between the St. Meinrad and Blue Creek coals, thus dating the outcrop to the mid-Atokan. Collectively, the data point to a marginal marine depositional environment with brackish and freshwater fluvial influence and occasional sub-aerial exposure.