Varimax-Rotated Visible Derivative Reflectance Spectroscopy of the Utica Shale / Point Pleasant Formation in Ohio
The Ordovician Utica shale is an extensive and significant portion of the Appalachian Basin subsurface, marking the transition from shallow water conditions to a deeper marine, tectonically active depositional environment. The Utica shale Play consists of calcareous shale and siltstone interbedded with limestone, creating a heterogeneous, complicated mixed siliciclastic-carbonate system. Generally, there is not a quick, accurate method for determining lithology, especially in core. Here, we present an approach previously used on loose sediment cores and apply it to rock cores of the Utica shale/Point Pleasant Formation, undifferentiated, to determine downcore mineralogy at a high-spatial resolution (1 cm). Three cores containing the Utica shale, the overlying Kope Formation, and underlying Lexington Limestone were analyzed using visible derivative reflectance spectroscopy at 1 cm spatial resolution. The data were processed with principal component analysis to extract mineral components, which were then verified with quantitative x-ray diffraction. The visible derivative reflectance spectroscopy detected illite and chlorite varying inversely with carbonate content throughout the cores. Iron oxides (hematite and goethite) were detected in one core, with a high concentration at the boundary between the Kope Formation and Utica shale, and various, lesser amounts throughout the rest of the core. The type and relative quantities of minerals detected via visible derivative reflectance spectroscopy of whole core were compared with mineral abundance determinations using quantitative X-ray diffraction analysis of ground samples. Calcite content was also quantitatively estimated using L*, the brightness of the core measured during reflectance spectroscopy. This estimated calcite content, along with two other previously measured cores, were then compared to the gamma ray core log to determine correlations between mineralogy and log signatures. Overall, the reflectance spectroscopy was able to provide quick, accurate, semi-quantitative information on the down-core mineralogy of these mixed siliciclastic-carbonate formations.
AAPG Datapages/Search and Discovery Article #90373 © 2019 AAPG Eastern Section Meeting, Energy from the Heartland, Columbus, Ohio, October 12-16, 2019