STRONTIUM ISOTOPE STRATIGRAPHY THROUGH THE LATEST PERMIAN MASS EXTINCTION EVENT AND PERMIAN/TRIASSIC BOUNDARY AT DAWEN, GREAT BANK OF GUIZHOU, SOUTH CHINA

One of the largest increases in seawater ⁸⁷Sr/⁸⁶Sr during the Phanerozoic occurred during the Late Permian and Early Triassic. Within this overall ⁸⁷Sr/⁸⁶Sr rise, the rate of change appears to be much greater for the Early Triassic compared to the Late Permian. However, improved calibration of the ⁸⁷Sr/⁸⁶Sr curve to biostratigraphy and geochronology in the Permian-Triassic boundary transition is needed to test hypotheses for what may have caused rates of rise to change. Several recent studies linked changes in the rate of ⁸⁷Sr/⁸⁶Sr increase to environmental perturbations during the extinction and Early Triassic recovery interval. In the present study, bulk carbonate samples from the Permian-Triassic boundary interval of Dawen, Great Bank of Guizhou, South China were analyzed for ⁸⁷Sr/⁸⁶Sr. These data are compared with other ⁸⁷Sr/⁸⁶Sr records from biostratigraphically constrained Permian-Triassic boundary sections. At Dawen, the least radiogenic ⁸⁷Sr/⁸⁶Sr values fluctuated between ~ 0.7071 in the late Changhsingian Clarkina changxingensis-deflecta conodont Zone and ~ 0.7072 in the Hindeodus parvus Zone. Our results are consistent with other studies and indicate that the rate of seawater ⁸⁷Sr/⁸⁶Sr rise increased significantly sometime after the start of the Triassic rather than at the latest Permian mass extinction horizon. Although this lag may be due to the long residence time of Sr in seawater, it also seems plausible that weathering of non-radiogenic basalt impacted the global seawater ⁸⁷Sr/⁸⁶Sr.