Progressive development of ocean anoxia in the end-Permian pelagic Panthalassa

Abstract

The end-Permian mass extinction (EPME) has been linked with the widespread development of oxygen-poor oceanic conditions. However, information on the spatial extent of anoxia in the Panthalassa super-ocean has been limited. This study reports oceanic redox records from a deep-sea chert succession (the Waiheke 1 section, WHK 1, New Zealand) that was located in southern mid-latitudes of Panthalassa. High-resolution carbon isotope (δ13C) correlation between Waiheke and the Permian-Triassic boundary (PTB) type section indicates that the EPME is recorded in a thin black claystone interbedded between siliceous mudstone beds at WHK 1. Pyrite-dominated enrichment in highly reactive iron, coupled with elevated U/Al and Mo/Al ratios, are prevalent through this black claystone bed and the overlying Permo-Triassic transition strata, suggesting the development of euxinic water column conditions. Similar redox variations across the EPME horizon have been reported from other Panthalassic deep-sea PTB sections. Comparison with these PTB sections indicates that euxinic conditions were widespread in low-latitude regions of the Panthalassan ocean, and such conditions developed earlier than in mid-latitude settings, up to 100,000 years before the EPME. This suggests there was a gradual expansion of ocean anoxia from low to middle-high latitude regions during the Permo-Triassic transition. The extent of ocean anoxia resulted in a decrease in the seawater inventory of redox sensitive trace metals (e.g., Mo), which is evident in the earliest Triassic strata of the studied section and other PTB sections. Panthalassic anoxia during the EPME coincides with extreme climate warming and the associated effects (e.g., changes in ocean circulation, marine eutrophication intensified by terrestrial weathering) were likely critical triggers for ocean deoxygenation.