Disentangling the Hettangian carbon isotope record: Implications for the aftermath of the end-Triassic mass extinction

This study provides an organic carbon stable isotope (delta C-13(org)) record calibrated with detailed ammonite biostratigraphy, following the end-Triassic biological crisis. Precise correlation between this crucial fossil group and the delta C-13(org) record is key to understanding feedbacks between biological and environmental events following mass extinction. The latest Triassic and Hettangian delta C-13(org) record shows several negative and positive excursions. The end-Triassic negative shift coinciding with the mass extinction interval is followed by a positive excursion in the earliest Hettangian Psiloceras spelae beds, which marks the onset of recovery in the marine ecosystem. This positive trend is interrupted by a second negative delta C-13(org) excursion in the P. pacificum beds related to a minor ammonite extinction event. This pattern of the delta C-13(org) curve culminates in the uppermost Hettangian Angulata Zone major positive excursion. This indicates that both the ecosystem and the carbon cycle remained in a state of perturbation for at least 2 Ma, although the recovery of some pelagic taxa already began at the base of Jurassic. The early and late Hettangian positive delta C-13(org) excursions have been confused in several recent papers. Here, we show that during the Hettangian there are indeed two distinct positive delta C-13(org) excursions. Phases of anoxia and further pulses of Central Atlantic Magmatic Province volcanism during the Hettangian might have inhibited the full recovery for that interval of time. The main Liasicus-Angulata organic positive CIE (carbon isotope excursion) during the Late Hettangian might be related to gradual decreasing of pCO(2) due to protracted high organic burial, and coincides with a second phase of recovery, as indicated by a pulse of ammonoid diversification.