LATE PERMIAN DOUBLE MASS EXTINCTION AND DOUBLE FELSIC VOLCANISM: G-L AND P-T BOUNDARY RECORD IN NORTHERN SICHUAN, SOUTH CHINA

Detailed stratigraphic analysis on the fossiliferous Middle-Upper Permian and Lower Triassic sequence at Chaotian in Sichuan, South China, identified two remarkable mass extinction horizons; i.e., the Guadalupian-Lopingian (G-L) and the Lopingian-Griesbachian (Permo-Triassic; P-T) boundaries. Across the G-L and P-T boundaries, biodiversity declined sharply in fusulinid, rugose coral, brachiopod, ammonite, conodont, and radiolaria. Both boundaries are characterized by two significant biohorizons, i.e., a major extinction level of pre-existing fauna (event horizon) and the first appearance datum (FAD) of younger fauna. The event horizons of both boundaries are intimately associated with peculiar fine-grained tuff beds with euhedral quartz, plagioclase, apatite, and zircon that suggest air-borne ash origin from felsic (rhyo-dacitic) source. At the G-L boundary, 2 m thick acidic tuff bed occurs, while 12 thin (several centimeter thick for each) tuff beds across the P-T boundary. These suggest that the Late Permian biosphere may have been perturbed twice by severe volcanism of felsic (non-basaltic) nature. Good regional correlation of the G-L and P-T boundary tuff beds among many sections in South China, and partly in Japan, strongly suggests a possible cause-effect relationship between the large-scale felsic thus explosive volcanism and mass extinction at the two boundaries. The apparently coeval Siberian and Emeishan trap volcanism of basaltic nature were often nominated for cause of these extinction events, however, direct link between these basaltic volcanisms and extinctions has not yet been fully documented.