Applying carbon-isotope stratigraphy using well cuttings for high-resolution chemostratigraphic correlation of the subsurface

Basin-scale correlations in the subsurface generally rely on lithostratigraphic information synthesized from wireline logs, and, in some cases, well cuttings, and cores. However, lithostratigraphic boundaries are often diachronous, and, as such, the correlations based upon them may not provide reliable timelines. In this paper, we use delta C-13(carb) data from well cuttings and a core to generate chronostratigraphic logs of Late Ordovician strata spanning the Black River Group, Trenton Group, and Utica Shale across the subsurface of New York State. Although particular delta C-13(carb) values may be impacted by (primary) variability in local dissolved inorganic carbon reservoirs and/or (secondary) diagenetic alteration, it is possible to identify spatially and stratigraphically coherent patterns in delta C-13(carb), which can be used to effectively correlate time-equivalent strata on a basin-wide (or even global) scale, including across lithologies (e.g., between limestone and calcareous shale). The present study emphasizes the use of well cuttings, as these are commonly collected during drilling and can provide the maximum lateral resolution for subsurface correlation. Parallel geochemical (percent carbonate and total organic carbon) and isotopic (delta O-18(carb) and delta C-13(org)) data are used to understand the origin of stratigraphic and spatial variability in the delta C-13(carb) signal and to identify diagenetic alteration. Stratigraphically coherent delta C-13(carb) trends across New York were used to identify six isotopically distinct packages of time-equivalent strata within these formations. Pairing chemostratigraphic and lithostratigraphic data improves our ability to document the diachronous nature of lithologic contacts, including the base of the Utica Shale, which is progressively younger moving west through New York.