MINERALOGICAL AND GEOCHEMICAL ANALYSIS OF THE BUTTER SHALES FROM THE WAYNESVILLE FORMATION (UPPER ORDOVICIAN) OF EASTERN INDIANA

The Waynesville formation (Richmondian) is a mixed Siliciclastic-Carbonaceous system consisting of alternating packages of offshore shales and shallow subtidal limestones situated near the top of the Cincinnati Arch (Ordovician) regional uplift. Several of these deep subtidal to offshore shales exhibit unique properties, such as high water content, distinct fossil communities, and a buttery texture. These shales, known as butter shales, occur in the Waynesville formation in Eastern Indiana along Hanna Creek near Brookville, Indiana (another occurrence of the butter shales can be found in Western Kentucky at the base of the Kope Formation (Hirnantian). Land management methods in the Cincinnati tri-state area are directly impacted by problems such as mass wasting. Therefore, study of the butter shale will allow improved policies and better local infrastructure efficiency. The properties exhibited in butter shales are a direct consequence of clay mineralogy and chemical composition not seen in other shales. The purpose of this study is to analyze the underlying structure (mineralogy and chemical composition) of the shale through X-ray Diffraction (XRD), X-ray Fluorescence (XRF), Scanning Electron Microcscope (SEM), and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) analysis to accurately describe the link between mineralogy and chemistry of these shales and the unique macroscopic properties they exhibit.

A total of 18 shale samples taken from two stratigraphic sections along the Hanna Creek outcrop north of Brookville, IN were collected for mineralogical and geochemical analyses. XRD was employed to analyze the mineralogical composition of the shale. XRF was used to understand the geochemical composition. SEM analysis was used to understand the microscopic textures of the shale. Rare earth element analysis was conducted using an ICP-MS. This study expects to find that the primary cause of the observed properties is based upon non-expandable clay mineralogy. Expected results involve determining chlorite or kaolinite polytype(s) to understand properties of the butter shales. Geochemical factors such as cation exchange capacities of different clays present are expected to play a secondary role in the shale’s behavior.