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.
The mass extinction at the Permian/Triassic boundary about 252 million years ago is the largest of the last half-billion years. It is famously defined by the loss of roughly 90% of all species in the ocean and a large fraction of life on land. Although there is still no agreement over the cause of this event, the favored opinions center on large-scale volcanism, climate change, loss of oxygen in the ocean—or a combination of these potentially coupled factors. Our work, which has involved the use of diverse geochemical tracers that allow us to interpret the conditions in the early ocean, is helping to resolve this debate. Specifically, our results for samples from central Japan reveal that oxygen-poor marine conditions occurred at least in this region well before the mass extinction but that those conditions intensified during the event. While the biotic impact of this intensification could have been significant, our data also reveal that severe oxygen loss was still limited to the mid depths of the water column, much like the oxygen minimum zones we see on biologically productive ocean margins today. Although deoxygenation was likely much more intense than in analogous modern settings, our findings challenge the popular idea of extreme, whole-ocean stagnation and anoxia at the Permian/Triassic boundary. Our research is challenging and refining other popular ideas about the loss of animal life at the Permian/Triassic boundary. Specially, data from northern Canada show that environmental changes, including the early impacts of volcanism and oxygen loss, were already having a deleterious effect on life at least in some regions well before the main event, which is marked by much larger-scale volcanism and anoxia. Most importantly, this research suggests that the Permian/Triassic boundary ‘event’ was more complicated than a single, brief episode. Instead, steps of environmental change seem to have occurred at different times at different locations across the globe. Now, we can better understand the ‘killing mechanisms’ behind Earth’s most famous and perhaps largest episode of extinction and the general ecological consequences of environmental changes throughout history, including those we face today.
