Catastrophic event sequences across the Permian-Triassic boundary in the ocean and on land

Abstract

This review forms the preface of a special issue dealing with Environmental stresses and biotic responses during the Palaeozoic-Mesozoic transition, and develops an improved understanding of the sequence of catastrophe events associated with the Permian-Triassic (P–Tr) transition in particular. The 16 papers that comprise this special issue mostly focus on the Paleo-Tethys and Panthalassia regions, and enable us to recognize seven distinct phases of biotic and environmental evolution that may be precisely correlated between marine and terrestrial environments. Phase 1 represents the normal marine environments and biota that existed at 252.104 Ma, prior to the onset of major environmental perturbation. Phase 2 is marked by the onset of a negative carbon (δ13Ccarb) isotopic excursion, and coincides with a significant decline in radiolarian diversity, the collapse of communities in shallow metazoan reefs and deep-water settings, and the loss of rainforests on land (including the disappearance of Gigantopteris flora). Phase 3 is characterized by a pulse of biodiversification on the eve of the end-Permian extinction (EPE). Phase 4 comprises the EPE event itself, dated to 251.941 Ma, and coincides with an extreme episode of widespread anoxia, biodiversity loss, community structural collapse, and volatile volcanic eruptions. Phase 5 is marked by the renewed onset of oxic conditions in all oceanic environments except those in microbialite-rich shallow platform settings where abundant pyrite framboids signal dysoxia. Phase 6 includes the earliest Triassic extinction (ETE) event, dated to 251.880 Ma, and associated with euxinic to anoxic conditions and ocean acidification. An extended phase of deoxygenation and acidification returned to the marine settings during Phase 7, possibly driving a calcium crisis. The terrestrial extinction event (Phase 2) probably commenced c. 60 kyrs (in South China) or 370 kyrs (in Sydney basin) before the marine P–Tr extinction, the latter consisting of two distinct events (Phases 4 and 6), spaced c. 60 kyr apart, each being marked by both a carbon isotope excursion and ecologic collapse. The environmental changes associated with these three extinction phases in the ocean and on land can be attributed to the effects of volcanic emissions (e.g., CO2, SO2, halogens and metals) during the eruption of the Siberian Traps Large Igneous Province and convergent margin volcanism related to Tethyan tectonics.