High Resolution XRF Stratigraphy of the Ordovician Utica Shale, Central New York State
Bulk rock elemental concentrations were collected using a handheld X-ray fluorescence spectrometer at 5 mm resolution through 5 m of core collected from the Utica Shale in central New York State. These results provide a higher resolution context to previous measurements from this core taken at stratigraphic scale of 7.62 cm (3 inches). While the two datasets are consistent, higher frequency trends are now resolvable and help to better understand the “signal to noise ratio” of the lower frequency data that extends over a much longer stratigraphic interval. Additionally, undetected elemental trends have been recognized below the resolution of the coarser dataset. The data collected in this study was also analyzed using a software package developed by the EPA called EPA PMF which uses positive matrix factorization, a form of multivariate factor analysis, to unmix the elemental concentrations of each sample into a set of geologically identifiable components. The stratigraphic trends in the contribution of these components can then be plotted to investigate changes in carbonate and biogenic silica content, the composition of siliciclastic detritus, and redox proxies. The results of this study suggest that short intervals of core through the various members of the Utica Shale and the associated Trenton Group limestones should be analyzed at high resolution to better understand the lower frequency datasets. By combining short intervals of high frequency data with longer intervals of low frequency data, collection rate and geologic resolution are not compromised.
AAPG Datapages/Search and Discovery Article #90335 © 2018 AAPG 47th Annual AAPG-SPE Eastern Section Joint Meeting, Pittsburgh, Pennsylvania, October 7-11, 2018