INFLUENCES OF ENVIRONMENTAL VARIATION AND SEDIMENTATION RATE ON THE RECORDING OF THE STEPTOEAN POSITIVE CARBON ISOTOPE EXCURSION (SPICE) IN MISSOURI

Carbon isotope compositions of marine limestone are thought to record perturbations of the global dissolved inorganic carbon reservoir. While pelagic limestones may best document the global open-ocean signal, in many cases, rocks available for study comprise shallow water carbonate environments in which local syn- and post-depositional processes may have complicated the temporal and stratigraphic patterns (Saltzman and Edwards, 2017; Schiffbauer et al., 2017; Yager et al., 2017). Examination of cores across a paleodepth gradient has revealed the time-transgressive, facies-dependent nature of the SPICE within upper Cambrian (Furongian) carbonates of the Central Missouri Intrashelf Basin. In the current study, we present new data (n = 132) from drill cores that reflect disparate depositional environments outside, but proximal to this basin: a thinner accumulation of platform carbonates deposited on the bathymetric high of the Lebanon Arch to the west of the basin and a thicker stratigraphic section of deep-ramp carbonates deposited on a fault block southeast of the basin, proximal to the Reelfoot Rift. The magnitudes of the SPICE offset (~ 5.5 ‰) and the maximum δ¹³C values of the SPICE (~ 4.5‰) in these cores are comparable to those documented for cores within the intrashelf basin (Schiffbauer et al., 2017). Initiation of the positive excursion coincides with an up-section shift to more shale-dominated lithologies, which appears to correspond to the transition from Sauk II to Sauk III transgression. Despite these similarities, the stratigraphic thicknesses over which the SPICE signal are expressed (rising and falling limb) vary by nearly an order of magnitude between the Lebanon Arch (5.2 and 7.6 m) and the fault block adjacent to the rift (48.8 and 70.3 m). This may suggest that sedimentation rate is a primary control on the manner in which the carbon isotopic signal is recorded in southern Missouri as deeper water bodies impinged on carbonate factories of the shallower environment.