Duration of and decoupling between carbon isotope excursions during the end-Triassic mass extinction and Central Atlantic Magmatic Province emplacement

Changes in δ¹³C_carb and δ¹³C_org from marine strata occur globally in association with the end-Triassic mass extinction and the emplacement of the Central Atlantic Magmatic Province (CAMP) during the break up of Pangea. As is typical in deep time, the timing and duration of these isotopic excursions has remained elusive, hampering attempts to link carbon cycle perturbations to specific processes. Here, we report δ¹³C_carb and δ¹³C_org from Late Triassic and Early Jurassic strata near Levanto, Peru, where intercalated dated ash beds permit temporal calibration of the carbon isotope record. Both δ¹³C_carb and δ¹³C_org exhibit a broad positive excursion through the latest Triassic into the earliest Jurassic. The first order positive excursion in δ¹³C_org is interrupted by a negative shift noted in many sections around the world coincident with the extinction horizon. Our data indicate that the negative excursion lasts 85±25 kyrs, longer than inferred by previous studies based on cyclostratigraphy. A 260±80 kyr positive δ¹³C_org shift follows, during which the first Jurassic ammonites appear. The overall excursion culminates in a return to pre-perturbation carbon isotopic values over the next 1090±70 kyrs. Via chronologic, isotopic, and biostratigraphic correlation to other successions, we find that δ¹³C_carb and δ¹³C_org return to pre-perturbation values as CAMP volcanism ceases and in association with the recovery of pelagic and benthic biota. However, the initiation of the carbon isotope excursion at Levanto predates the well-dated CAMP sills from North America, indicating that CAMP may have started earlier than thought based on these exposures, or that the onset of carbon cycle perturbations was not related to CAMP.