Middle Permian (Capitanian) seawater 87Sr/86Sr minimum coincided with disappearance of tropical biota and reef collapse in NE Japan and Primorye (Far East Russia)

Abstract

To investigate the secular changes in Permian seawater chemistry and to constrain the global environmental changes during the end-Guadalupian (Middle Permian) extinction, we analyzed 87Sr/86Sr ratios in Capitanian (Upper Guadalupian) shallow-marine limestones in NE Japan and in southern Primorye, Far East Russia. These limestones were deposited on the continental shelf/platform of the northern part of Greater South China, which faced the northern connecting seaway between the Tethys and Panthalassa. The measured limestone samples were collected from the Capitanian fusuline (Lepidolina)-bearing intervals and overlying beds at Iwaizaki in the South Kitakami belt, NE Japan, and at Senkina Shapka in the Sergeevka belt, southern Primorye. The present analysis of bulk 87Sr/86Sr ratios clarified extremely low 87Sr/86Sr ratios of 0.7068–0.7070 from all measured samples. These Sr isotopic values support a Capitanian age for these strata. The topmost 30 m-thick interval of the Iwaizaki Limestone, in particular, witnessed a stepwise biodiversity decline in the shallow marine warm-water biota and the collapse of the carbonate factory after the reef development during the Capitanian in the northern part of Greater South China. The disappearance of the tropical biota and the collapse of the reef during the late Capitanian suggest that the biotic responses to a significant environmental change appeared relatively earlier at mid-latitudes than in the tropical regions.