CLAY MINERALOGY OF THE KOPE AND MARTINSBURG FORMATIONS: EVALUATING THE POTENTIAL USE OF ORDOVICIAN SHALES AS GEOTHERMOMETERS AND ENVIRONMENTAL REFERENCE MATERIALS IN THE APPALACHIAN BASIN
A preliminary comparison of powder X-ray diffraction (XRD) patterns of stratigraphically equivalent samples from the Upper Ordovician Kope (northern Kentucky) and Martinsburg Formation (eastern PA) indicates a difference in crystallinity in illite measured at FWHM values consistent with existing thermal history data. For the < 2 µm size fraction, the Kope Formation has FWHM values of 0.347 and 0.445. FWHM values increase with decreasing particle size above Scherrer equation boundary conditions (300 nm). FWHM values for Martinsburg samples vary from approximately 0.170 to 0.210. XRD analyses indicate both Kope and Martinsburg shales have ripidolite of similar chemical compositions. The similarity of the mineralogy suggests experiments and analytical work comparing the two formations in the context of thermal maturation and environmental evaluation is appropriate. Scanning electron microscoscopy and transmission electron microscopy indicate that minor mineralogical diversity differences between the two units that likely reflect sediment source variations.