The Time-Transgressive Deposition of the Utica Shale in New York Revealed Using Carbon Isotope Stratigraphy

Metzger, John G.; Fike, David; Smith, Taury

Carbon isotope ratios of dissolved inorganic carbon in the surface ocean are well-mixed and change through time. These trends are recorded in marine carbonates and carbonate cements (δ¹³Ccarb) and provide a means for high-resolution chronostratigraphic correlation in carbonates and carbonate-bearing siliclastic sequences. In contrast to absolute chronostratigraphy, which utilizes absolute ages obtained from radiogenic isotopes (e.g. U-Pb ages from volcanic ashes) a relative chronostratigrapy can be constructed for sections using δ¹³Ccarb, as this record is time-dependent and should vary synchronously between sections. The resulting level of temporal correlation (down to 10⁴ yrs) meets or exceeds the analytical precision of current radiogenic isotope based dating methods as well as biostratigraphic methods. Well-resolved δ¹³Ccarb trends reveal the time-transgressive relationship between the Utica Shale in eastern New York and the Trenton Limestone of western and central New York. Calculated sedimentation rates suggest that the onset of the carbonate-rich Utica Shale in the east falls chronologically earlier (by 10⁵ - 10⁶ yrs) than the carbonate-poor Utica in the west. Correlations show the Utica contact is increasingly younger across New York, consistent with a migrating depositional facies. This work, carried out using samples from well cuttings and cores, supports previous stratigraphic relationships proposed for the Utica-Trenton outcrop belt using detailed biostratigraphic and K-bentonite data. The successful demonstration of δ¹³Ccarb in producing robust correlations through the subsurface highlights the potential that δ¹³Ccarb chemostratigraphy may have for answering other high-resolution stratigraphic questions in areas where outcrops are stratigraphically incomplete, scarce, or absent.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013