Dynamic anoxic ferruginous conditions during the end-Permian mass extinction and recovery

M O Clarkson,S A Kasemann,F Bowyer,S Richoz,R A Wood,S W Poulton,L Krystyn,R J Newton

doi:10.1038/ncomms12236

Abstract

The end-Permian mass extinction, ∼252 million years ago, is notable for a complex recovery period of ∼5 Myr. Widespread euxinic (anoxic and sulfidic) oceanic conditions have been proposed as both extinction mechanism and explanation for the protracted recovery period, yet the vertical distribution of anoxia in the water column and its temporal dynamics through this time period are poorly constrained. Here we utilize Fe–S–C systematics integrated with palaeontological observations to reconstruct a complete ocean redox history for the Late Permian to Early Triassic, using multiple sections across a shelf-to-basin transect on the Arabian Margin (Neo-Tethyan Ocean). In contrast to elsewhere, we show that anoxic non-sulfidic (ferruginous), rather than euxinic, conditions were prevalent in the Neo-Tethys. The Arabian Margin record demonstrates the repeated expansion of ferruginous conditions with the distal slope being the focus of anoxia at these times, as well as short-lived episodes of oxia that supported diverse biota.

Highlights

The end-Permian mass extinction, B252 million years ago, is notable for a complex recovery period of B5 Myr
This unique depth transect allows for a well-resolved vertical and temporal record of regional redox dynamics within an established carbon isotope and biostratigraphic framework[20,23,24,27].We identify a temporally and spatially dynamic redox system that shows expansions of anoxic ferruginous conditions across the Arabian Margin
FeHR refers to Fe minerals that are considered highly reactive towards biological and abiological reduction under anoxic conditions, and includes carbonate-associated Fe (Fecarb; for example, ankerite and siderite), ferricoxides (Feox; for example, goethite and haematite), magnetite Fe (Femag) and Fe sulfide minerals (Fepy; for example, makinawite and pyrite)

Summary

Introduction

The end-Permian mass extinction, B252 million years ago, is notable for a complex recovery period of B5 Myr. Despite suggestions of the extreme redox state of euxinia[4,6], no redox studies have yet employed methods capable of distinguishing anoxic ferruginous conditions from euxinic conditions across the full Permo-Triassic extinction and recovery interval This is critical as the precise nature of water column chemistry during periods of anoxia has profound implications for the evolution of the biosphere and for feedbacks associated with the biogeochemical cycling of elements such as nitrogen[16] and phosphorus[14] in the sediment and water column. Our samples primarily span from the Late Permian (B260 Ma), across the extinction interval (EI) and the Permian Triassic Boundary (PTB), to the Late Spathian This unique depth transect allows for a well-resolved vertical and temporal record of regional redox dynamics within an established carbon isotope and biostratigraphic framework[20,23,24,27].We identify a temporally and spatially dynamic redox system that shows expansions of anoxic ferruginous conditions across the Arabian Margin. Our data demonstrate short-lived interludes of oxic water column conditions, which in contrast to ferruginous episodes are characterized by a diverse fossil record, suggesting that biotic recovery in the Neo-Tethys was rapid during these oxygenation episodes

Methods

Results

Conclusion