MARINE ENVIRONMENTAL RESPONSES TO VOLCANISM IN THE LATEST CHANGHSINGIAN OF SOUTH CHINA: EVIDENCE FROM PENGLAITAN, GUANGXI

The Penglaitan section, located in Guangxi, China, experienced extremely rapid sedimentation in the last 200 kyr of the Permian, making it among the highest-resolution extant records of marine conditions leading up to the end-Permian extinction. The Changhsingian section, exposed along the bank of the Hongshui River, is approximately 700 meters. While most of the section is composed of decimeter-scale distal turbidites of mixed carbonate and clastic composition, reflecting a submarine distributary fan, a general shallowing-upward sequence culminates in an interval of subaerial deposition, followed by a final 70 meters of marine sedimentation preceding the main extinction horizon. This study will focus on the rare earth, trace element, and isotopic geochemistry of this final marine interval representing approximately 100 kyr of latest Changhsingian deposition in a relatively shallow platform-top environment. The Eu anomaly and Th/Sc ratio of sediments identify intervals of increased rhyolitic ash input which, as they are interbedded with massive, immature coarse sandstones composed largely of mafic minerals, likely reflect local volcanism along the subduction margin of the South China microcontinent. These inputs of ash are associated with numerous disturbances to the marine ecosystem, including evidence for suboxic bottom water conditions. Minor positive organic carbon isotope excursions, and disturbances to the nitrogen cycle, suggest that this intermittent suboxia may have been driven by transient increases in marine productivity or the flux of terrestrial organic material to the basin, driving increased biological oxygen demand in the porewater environment and increased sedimentary denitrification. While no evidence for lethally euxinic conditions is detected prior to the main extinction horizon, the section reflects processes that may have stressed shallow-water environments and contributed to shoaling of the chemocline prior to the end-Permian extinction.