The causes and dynamics of the Permian-Triassic boundary (PTB) mass extinction, the largest in Earth history, remain uncertain. Gradual deterioration of marine and terrestrial environments during the Late Permian and persistence of inhospitable conditions through the Early Triassic suggest that intrinsic factors were important, but an extinction rate peak, abrupt lithofacies changes, and geochemical anomalies associated with the end-Permian event horizon are evidence of a catastrophic event (e.g., massive volcanic eruption, bolide impact, and/or large-scale oceanic overturn). Despite long study of the PTB, there are remarkably few integrated, high-resolution chemostratigraphic studies of marine boundary sections that can address critical questions related to the extent and intensity of Permo-Triassic deep-ocean anoxia, patterns of upwelling of toxic deep-ocean waters onto shallow-marine shelves and platforms, the relationship of such events to contemporaneous changes in seawater carbonate saturation and to the delayed recovery of marine biotas, controls on the post-extinction global negative C-isotope shift, and the relative timing and causal relationship of PTB crises in the marine and terrestrial realms. In this project, we propose to generate geochemical proxy datasets consisting of magnetic susceptibility, elemental concentrations, TOC-TIC, ?Ô13Ccarb-?Ô13Corg, S-Fe speciation, ?Ô34Ssulfide-?Ô34Ssulfate, REEs, and biomarkers for a total of 19 sections in eight study areas, including 8 sections in four areas of the former Panthalassic Ocean (the Cache Creek terrane, Western Sedimentary Basin, and Sverdrup Basin of Canada, and the Maitai-Waipapa terranes of New Zealand) and 11 sections in four areas of the former Tethys Ocean (Vietnam-China, India, Iran, and Italy). Conodont biostratigraphy combined with C-isotope and MS event stratigraphy will facilitate correlations within and between study areas. Paleoceanographic modeling will be used to investigate the effects of potential forcings on Permo-Triassic ocean chemistry and sedimentary fluxes, and comparisons with globally integrated chemostratigraphic datasets will allow refinement of model simulations. This project has the potential to yield important new findings regarding events at the Permian-Triassic boundary and key insights regarding proximate and ultimate controls on contemporaneous chemical oceanographic perturbations. Investigation of catastrophic climate and environmental change associated with the largest mass extinction in Earth history should be of considerable interest to both the Earth-science community and the scientifically literate public. The broader impacts of the project are varied and include public outreach and dissemination of project results, mentoring of undergraduate and graduate students, development of research synergies among a diverse group of geoscience professionals, and the potential for results of broad scientific significance. The PIs are committed to training the next generation of scientists (they have collectively supervised ~60 graduate students, and all are actively engaged in advising and training undergraduate students), to advancing science education in the public schools, and to achieving greater ethnic and gender diversity among these future scholars (Algeo and Ellwood are both involved in programs to recruit minority students). Project datasets funded through NSF will be made available to the larger scientific community through CHRONOS and PaleoStrat.
Project Summary: The causes and dynamics of the Permian-Triassic boundary (PTB) mass extinction, the largest biocrisis in Earth history, during which ~90% of marine species disappeared, remain incompletely understood. This project investigated changes in marine environmental conditions during the crisis and the prolonged (~5-million-year) interval of recovery of marine ecosystems following the mass extinction. The project analyzed about 30 PTB sections with a near-global distribution in order to document environmental changes during this crisis. Among the key findings of this study are evidence of (1) sustained euxinia in intermediate-depth settings prior to the mass extinction, probably due to an expansion of oceanic oxygen-minimum zones, (2) brief episodes of euxinia in shallow-marine settings at the PTB, (3) increased erosion in land areas and flux of nutrients to coastal seas, and (4) intensified water-column stratification, resulting in reduced vertical overturning circulation (Figures 1-2). All of these oceanographic changes were probably linked to rapid buildup of greenhouse gases (principally CO2 and CH4) in the latest Permian atmosphere, probably as a consequence of massive eruptions of flood basalts in the Siberian Traps province and concurrent magmatic intrusions into the West Siberian Coal Basin. The climatic and environmental consequences of these eruptions persisted strongly for ~2 million years, before partially abating during the late Early Triassic and then disappearing in the Middle Triassic. Intellectual Merit: The broader significance of this problem is that it is likely to provide insights into ecosystem changes that may result from modern-day climatic and environmental changes of anthropogenic origin. Changes in nutrient fluxes related to agricultural runoff and pollution have begun to have a large impact on coastal marine environments, leading to (among other effects) more than 400 coastal ‘dead zones’ globally. Whereas the consequences of climate change on the physical and chemical conditions of the world’s oceans can be modeled on the basis of first principles, the biotic consequences of such change are unpredictable and not readily amenable to study through modeling. Our best guide to the potential effects on marine organisms and ecosystems is the geologic record of major environmental perturbations and mass extinctions in the Earth’s past. The Permian-Triassic boundary biocrisis represents the largest such crisis in the geologic record, and it shares some important characteristics with the unfolding modern environmental crisis, including major perturbations to nutrient cycles, fluctuations in marine productivity, and expanded areas of oceanic anoxia. Broader Impacts: The results of this study provide significant new insights regarding the nature of marine environmental deterioration that led to a 90% kill rate during the PTB mass extinction (see above). Project results were made public in a series of 43 technical papers and 68 presentations at professional meetings, and the datasets generated during this study will be made available to the larger scientific community through PaleoStrat and ResearchGate. The project provided research opportunities for about 10 graduate students and 25 undergraduate students, and, thus, served to help train the next generation of geoscientists. The PIs also sought to advance science education in the public schools through public outreach activities.
