KILLER VOLCANISM AT THE GUADALUPIAN-LOPINGIAN BOUNDARY (PERMIAN): NOT BASALTIC BUT ACIDIC

The greatest mass extinction in the Phanerozoic occurred at the end of the Paleozoic in a double-phased manner, i.e., first at the Guadalupian-Lopingian (or Middle-Late Permian) boundary (GLB) and second at the bona fide Permo-Triassic (Lopingian-Griesbachian) boundary (PTB). The greatest magnitude of the end-Paleozoic catastrophe throughout the Phanerozoic may have resulted from two distinct biospheric perturbations within a short time interval less than 10 m.y., although the ultimate cause is still unknown. Finding a unique acidic tuff bed at the GLB horizon both in South China and Japan suggests the enrollment of a violent volcanism to the global environmental change across the GLB. An acidic tuff bed (ca. 2 meter thick) is observed exactly at the GLB horizon in many sections in South China including Shansi, Huanying (Sichuan), Laibin (Guanxi) etc. The occurrence of the acidic tuff bed in 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 Jurassic, the paleo-seamount with atoll limestone on top of it was located in the mid-oceanic domain at the GLB timing, probably more than 3000 km away from the continental margin. Thus the source volcanism should have been violent enough to cover with ash the western superocean Panthalassa in addition to the whole South China in the eastern Pangea. The geochemistry of this volcanism appears concordant with the supposed violent eruption but is quite distinct from those of the continental flood basalt such as the Siberian Traps that has been often nominated as one of the favorite candidates for the cause of the PTB event. From a paleoenvironmental aspect, it is noteworthy that the PTB superanoxia in the deep superocean started at this timing of the GLB volcanism.