Astronomical Time Scale Calibration of the Early Jurassic Sinemurian-Pliensbachian Boundary Event and Global Carbon Cycle Perturbation: Prees Core, Cheshire Basin, Uk (icdp Jet Project)

Large Igneous Province volcanism profoundly influenced the Earth system, driving recurrent episodes of global climatic, environmental, and palaeoceanographic instability during the early Jurassic. The carbon cycle perturbations at the Triassic–Jurassic transition and during the Toarcian Oceanic Anoxic Event (T-OAE) are relatively well constrained, the timing, duration, and underlying mechanisms of intervening early Jurassic carbon cycle perturbations remain poorly resolved. In particular, the cause and magnitude and timing of the Sinemurian–Pliensbachian (S–P) negative carbon isotope excursion (CIE), globally observed in marine and continental sedimentary archives and concomitant with geographically widespread environmental and depositional changes remains unconstrained. Here, we present new data from a ~271 m thick stratigraphic interval in the Prees–2 core of the Cheshire Basin (England, UK), spanning the S–P transition including Upper Sinemurian topmost semicostatum, turneri, obtusum, oxynotum and raricostatum ammonite zones as well as the Lower Pliensbachian jamesoni and ibex ammonite zones. The δ13Corg and δ13Cwood data obtained in this study shows a ~3‰ negative CIE in across the S–P transition. ITRAX X-ray fluorescence (XRF) elemental data records from Prees–2 was cyclostratigraphically analyzed, and shows a hierarchy of dominant periodic variations, module by the Milankovitch frequencies. A meta-analysis of Sinemurian and Pliensbachian ammonite zonal duration estimates of Prees–2 this study and previously published studies, used to construct a robust global Astronomical Time Scale (ATS), yielding durations of ~7±0.25 Myr and ~8.2±0.31 Myr, respectively. The duration of the S–P negative CIE duration obtained as ~4.6 Myr. Combined with published radio-isotopic age constraints for the Triassic–Jurassic and Pliensbachian–Toarcian stage boundaries, we here constrain the ages of the Hettangian–Sinemurian and Sinemurian–Pliensbachian boundaries as 198.89 ±0.55 Ma and 191.88±0.46 Ma, respectively.