Middle-Upper Permian (Maokouan-Wuchiapingian) boundary in mid-oceanic paleo-atoll limestone of Kamura and Akasaka, Japan

Nearly 10 million years before the Permo-Triassic boundary (PTB; ca. 251 Ma ) characterized by the greatest mass extinction in the Phanerozoic, the Mid dle-Upper Permian boundary marked another big biotic decline almost compara ble in magnitude to the PTB event. Two stratigraphic sections spanning acro ss the Maokouan (Middle Permian)-Wuchiapingian (Upper Permian) boundary (MW B) were. newly found in paleo-atoll limestone within the Jurassic accretion ary complex in Kamura and Akasaka, Japan, These two sections share almost i dentical litho- and biostratigraphy that records a remarkable biotic extinc tion of large-shelled fusulinids and a sharp lithologic change exactly acro ss the MWB. These new data, as the first evidence from the shallow-water mi d-oceanic realm, suggest that a quick environmental change occurred in a gl obal scale across the MWB. A thin, acidic tuff recognized at the MWB horizo n in the paleoatoll limestone has a potential utility as a key bed for glob al correlation and suggests a possible link between the end-Permian biosphe re crisis and the explosive acidic volcanism.