2001 Volume 77 Issue 6 Pages 104-109
Nearly 10 million years before the Permo-Triassic boundary (PTB; ca. 251 Ma) characterized by the greatest mass extinction in the Phanerozoic, the Middle-Upper Permian boundary marked another big biotic decline almost comparable in magnitude to the PTB event. Two stratigraphic sections spanning across the Maokouan (Middle Permian)-Wuchiapingian (Upper Permian) boundary (MWB) were newly found in paleo-atoll limestone within the Jurassic accretionary complex in Kamura and Akasaka, Japan. These two sections share almost identical litho- and biostratigraphy that records a remarkable biotic extinction of large-shelled fusultnids and a sharp lithologic change exactly across the MWB. These new data, as the first evidence from the shallow-water mid-oceanic realm, suggest that a quick environmental change occurred in a global scale across the MWB. A thin, acidic tuff recognized at the MWB horizon in the paleoatoll limestone has a potential utility as a key bed for global correlation and suggests a possible link between the end-Permian biosphere crisis and the explosive acidic volcanism.