Constraining the cause of the end-Guadalupian extinction with coupled records of carbon and calcium isotopes

A negative δ C 13 excursion in carbonate sediments near the Guadalupian/Lopingian (Middle/Late Permian) boundary has been interpreted to have resulted from a large carbon cycle disturbance during the end-Guadalupian extinction event (ca. 260 Ma). However, the carbon isotope data alone are insufficient to uniquely determine the type and magnitude of perturbation to the global carbon cycle. Calcium isotopes can be used to further constrain the cause of a carbon isotope excursion because the carbon and calcium cycles are coupled via CaCO3 burial. In this study, we present coupled carbon and calcium isotope records from three Guadalupian–Lopingian (G/L) sections in China (Penglaitan and Chaotian) and Turkey (Köserelik Tepe). The δ C 13 and δ Ca 44 / 40 records differ among our studied sections and do not co-vary in the same manner. No section shows δ C 13 and δ Ca 44 / 40 changes consistent with massive, rapid volcanic CO2 emissions or methane clathrate destabilization. Additionally, many sections with large ( > 3 ‰ ) changes in δ C 13 exhibit δ O 18 evidence for diagenetic alteration. Only one section exhibits a large excursion in the δ Ca 44 / 40 of limestone but the absence of a similar excursion in the δ Ca 44 / 40 of conodont apatite suggests that the limestone excursion reflects a mineralogical control rather than a perturbation to the global calcium cycle. Hence, we interpret the large isotopic changes observed in some sections to have resulted from local burial conditions or diagenetic effects, rather than from a large carbon and calcium cycle disturbance. Perturbations to the global carbon and calcium cycles across the G/L transition were much less intense than the disturbances that occurred across the subsequent Permian–Triassic boundary. This finding is consistent with the much smaller magnitude of the end-Guadalupian extinction relative to the end-Permian.