MINERALOGY OF THE POINT PLEASANT FORMATION WITHIN THE SEBREE TROUGH, SW OHIO, USING VNIR SPECTROSCOPY AND XRD

The Sebree Trough is a Late Ordovician age depositional low extending from NE Kentucky, through SW to central Ohio, between and contemporaneous with the Trenton and Lexington carbonate platforms. Shale, siltstone, and carbonate filled the basin and accumulated on top of the surrounding platforms, forming the Point Pleasant Formation in Ohio. Here, we examined the compositional variations for two cores, one within the Sebree Trough and one on the SE ramp leading onto the Lexington Platform, using visible and near infrared (VNIR) spectroscopy, quantitative X-ray diffraction (XRD) and carbon coulometry in order to identify changes within the mineralogy. VNIR was measured at a much finer spatial resolution (1 cm) down core, and XRD samples were taken at representative facies to verify VNIR results. The Point Pleasant Formation mostly consists of various phyllosilicates (chlorite, illite and muscovite), quartz, calcite, dolomite, albite, pyrite and hematite, as identified by XRD. For the core located in the Sebree Trough, quartz content remains relatively constant throughout (~19%); calcite is generally low (typically <15%) and peaks (~57%) near the upper boundary of the Point Pleasant; the clay content is negatively correlated with the calcite content (higher concentrations of clays where lower concentrations of calcite are measured, and vice versa, as measured by XRD). The clay content is mostly illite, with lesser amounts of chlorite and muscovite, and the overall average of clay content throughout the core is ~55%. On the SE ramp of the trough, there are several beds of mostly or all carbonate content (90%+). The overall average clay content is ~41% throughout this core, and the quartz content remains fairly constant for beds where carbonate does not dominate (~19%). VNIR was able to detect calcite and clay variability qualitatively, and was generally consistent with the XRD results. These results generally indicate four pulses of carbonate influx into the trough, with the extent varying across the region, and confirming concurrent shale and carbonate deposition across the region.