A carbon-isotope perturbation at the Pliensbachian-Toarcian boundary: evidence from the Lias Group, NE England

A perturbation in the carbon-isotope record at the time of the Pliensbachian-Toarcian boundary (~ 184 Ma) in the Early Jurassic is reported, based on new data from Yorkshire, England. Two sharp [delta][sup.13][C.sub.org] negative excursions, each with a magnitude of ~ -2.5 [per thousand] and reaching minimum values of -28.5 %o, are recorded in the bulk organic-matter record in sediments of latest Pliensbachian to earliest Toarcian age. A similar pattern of negative carbon-isotope excursions has been observed at the stage boundary in the SW European section at Peniche, Portugal in [delta][sup.13][C.sub.carbonate], [delta][sup.13][C.sub.wood] and [delta][sup.13][C.sub.brachiopod] records. The isotopic excursion is of interest when considering the genesis and development of the later Toarcian Oceanic Anoxic Event (OAE), as well as the second-order global extinction event that spans the stage boundary. Furthermore, the isotope excursion potentially provides a chemostratigraphic marker for recognition of the stage boundary, which is currently achieved on the basis of different ammonite faunas in the NW European and Tethyan realms. Keywords: Jurassic, Toarcian, Pliensbachian, carbon-isotope, excursion. doi: 10.1017/S0016756809990458