REEF ECOSYSTEM COLLAPSE AND BIOTIC EXTINCTION COINCIDE WITH VOLATILE VOLCANISMS AND ANOXIA OVER GUADALUPIAN-LOPINGIAN (PERMIAN) TRANSITION

The Captanian mass extinction is actively debated, with its timing, validity, and causality all questioned. Here we show, based on detailed sedimentary, petrographic, palaeoecologic and geochemical analyses of the Guadalupian–Lopingian (Middle–Late Permian) Global Stratotype Section and Point (GSSP) at Penglaitan (South China) that the Guadalupian–Lopingian Boundary (GLB) crisis is characterized by a slightly earlier collapse of reef systems followed by benthic extinction. This disaster is separated from the mid-Capitanian extinction by an interlude phase when an extraordinarily diverse reef ecosystem was developed. This contains diverse bryozoans and coral frame-builders along with the youngest occurrence of the giant, aberrant alatoconchid bivalves, a group that had been thought extinct by mid-Capitanian. This group, and perhaps some of the bryozoans, brachiopods, corals, and foraminifers, went extinct at the end of the Capitanian. Mercury concentration/Total organic content (Hg/TOC) ratios show two anomalies, revealing the possible eruption pattern of the Emeishan Large Igneous Province (ELIP) near the GLB. The first Hg/TOC peak is moderate and represents the onset of reactivation of ELIP after mid-Capitanian, which coincided with the collapse of the end-Capitanian reef ecosystem, a large positive shift in Chemical Index Alteration (CIA), and onset of a microbial bloom. A much larger Hg/TOC peak occurs just above the GLB and represents the main eruption episode of ELIP. This volatile volcanism coincided with benthic extinction, large negative carbon isotope excursion, oceanic anoxia as indicated by both sulfur isotopes and pyrite framboid analysis, and abrupt rise in sea-level. The temporal coincidence of these phenomena supports the idea of a cause-and-effect relationship, and that the volatile eruption of ELIP during the Guadalupian–Lopingian transition likely triggered the GLB extinction.