END-PERMIAN DOUBLE-PHASED MASS EXTINCTION AND KILLER VOLCANISM

The end-Permian mass extinction actually comprises two distinct events occurred back to back; the first one at the Guadalupian-Lopingian (or Middle-Late Permian) boundary (GLB) and the second at the bona fide Permo-Triassic boundary (PTB). The greatest magnitude of the catastrophe throughout the Phanerozoic may have resulted from two distinct biospheric perturbations within a short time interval less than 10 m.y. The occurrence of acidic tuffs not only at the PTB but also at the GLB suggests the enrollment of violent volcanism to the global environmental change across the two remarkable extinction horizons. For example, an acidic tuff bed (ca. 2 meter thick) is observed exactly at the GLB horizon in many sections in South China. The occurrence of acidic tuff bed from a mid-oceanic paleo-atoll limestone in Japan at the same horizon suggests extensive distribution of air-borne ash over thousands of kilometer. Before the tectonic accretion to the Japan margin in the Middle Jurassic, the atoll-capped paleo-seamount was located somewhere in mid-ocean of the Late Permian Panthalassa, probably more than 3000 km away from the continental margin. Thus the source volcanism of acidic nature should have been violent enough to spread ash over the western superocean Panthalassa, in addition to the whole South China on the eastern Pangea. The geochemistry of this volcanism supports the violent eruption scenario but it is quite distinct from those of the continental flood basalt such as the Siberian Traps and Emeishan flood basalt that have been often nominated as favorite candidates for the cause of the GLB and PTB events. From a paleoenvironmental aspect, it is noteworthy that the superanoxia in the deep superocean started from the GLB and culminated across the PTB.