GEOCHEMISTRY OF THE UTICA SHALE USING A PORTABLE XRF AS A MAPPING TOOL

The Utica Shale is a black calcareous, organic-rich shale of Upper Ordovician age known for its significant quantities of natural gas, natural gas liquids, and crude oil. It also reflects a profound change in the tectonics of the Northeast by marking the onset of deposition resulting from convergent tectonics to the east during the Taconic Orogeny.

In this study, we wanted to determine if we could distinguish Utica Shale above and below (upper Indian Castle and lower Indian Castle members, respectively) the Honey Hill Disconformity, using published XRF data (Pietras and Spiegel, 2018) previously conducted on a drill core through both members. The differing elemental concentrations above and below the Honey Hill Disconformity may provide an accurate mapping tool using field samples and a portable XRF to separate these two members on maps. Pietras and Spiegel’s data show that the Lower Indian Castle member differs from the upper member by greater concentrations of calcium, and lower concentrations of aluminum and silicon, reflecting a change in carbonate and aluminum-silicate mineral compositions.

For our study, a total of 15 rock samples were collected from three different areas in the western Mohawk Valley of Central New York State. Eight samples were collected from Nowadaga Creek, (four samples were collected from one side of the creek and four from the other side), four samples were collected from a roadside outcrop near Hallsville, and three were collected in Reall’s Creek in Deerfield. Whole rock powders were ground in a tungsten carbide shatterbox and analyzed with a Hitachi XMET-8000 portable XRF. Our measurements were compared with data from Pietras and Spiegel (2018). Results from our analysis show that the core data from Pietras and Spiegel (2018) can be replicated using field samples indicating that a portable XRF may be a useful mapping tool when a good reference column exists.