The Permian-Triassic transition in ocean island setting: Environmental disturbances and new high-resolution carbon-isotope record from the Qiangtang Basin, NW China

Abstract

The Permian-Triassic boundary (PTB) events such as carbon-isotope excursion, volcanism, and environmental disturbances are not well understood in an ocean island setting. Here, we develop a new case study for the Permian-Triassic transition in the Qiangtang Basin, Tibet, by combining existing biostratigraphy, new carbon-isotope data, sedimentological data, UPb zircon age, mineralogical and geochemical data. These new data defined the Permian-Triassic transition age as about 252.3 ± 0.9 Ma, corresponding to the lowermost sea level. A long-term negative carbonate carbon isotope trend is present at the same stratigraphic level in different depositional environments, strongly suggesting its global nature. However, our new ocean island setting is characterized by an abrupt shift in carbon isotope values across the level, which is different from many chemostrtigraphic studies that show a gradual shift in carbon isotope values across the event horizon. The most likely explanation for the abrupt shift in δ13C values is a sedimentary hiatus at this level in the study section. Three-stage climatic models through the PTB in the ocean island setting are identified: Stage 1 is characterized by a warm and humid climate with moderate chemical weathering; while a hot and humid climate with intense chemical weathering dominates stage 2; the climate in stage 3 is a relatively hot and arid climatic condition with weak chemical weathering.