Sedimentology, geochemistry, and paleobiology of a Pennsylvanian marginal marine depositional environment, Mansfield Formation, Indiana
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2013, Sedimentology, geochemistry, and paleobiology of a Pennsylvanian marginal marine depositional environment, Mansfield Formation, Indiana: Indiana Geological Survey Occasional Paper 71, 18 p., 8 fig., 0 pl.
Outcrops of the Pennsylvanian Mansfield Formation in Martin County, Indiana, were examined to integrate sedimentological, geochemical, and paleobiological data for refinement of local paleoenvironment and age designation. The stratigraphically older HR-150 outcrop contains in the lower section a combination of wavy-, flaser-, and ripple-bedded silty and very fine grained sandstone, overlain first by dark gray, friable, clayey siltstone, then by laminated, wavy- and planar-bedded siltstones with clay drapes. Geochemical analysis shows that all total sulfur values are <0.2 weight percent, with most values well below 0.04 by mass. Total organic carbon ranges from <0.1 to 0.4 by mass except for a thin layer of organic-rich, friable siltstone with coal inclusions where TOC is slightly under 13 wt percent by mass. Total organic carbon/total sulfur ratios vary from 1:1 in the lower to 76:1 in the upper section. Feeding trace fossils occur in the lower section of the outcrop, and vertical burrows are common at the top. The stratigraphically younger H-435 outcrop contains friable siltstone overlain by a coal seam near the base, with beds of wavy and laminated sandstones with ripples, roots, and clay drapes composing the rest of the section. Total sulfur is 0.6 to 0.7 wt percent in the coal seam and near or below 0.1 wt percent in the rest of the outcrop. Total organic carbon varies from 51.4 to 66.8 wt percent in the coal seam and is below 0.15 wt percent above the seam. Total organic carbon/total sulfur ratios vary from 122.4:1 to 1.7:1. Trace fossils indicative of feeding behavior are common, although insect repichnia or pascichnia and tetrapod tracks also occur. Palynological analyses of samples extracted from the coal seam limit the upper age of the stratigraphically younger H-435 outcrop to the early Atokan. Sedimentology, geochemistry, and paleobiology point to a fluviodeltaic paleoenvironment with negligible marine influence for both outcrops.
Keywords: sedimentology, geochemistry, paleobiology, Mansfield Formation
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