ROLE OF TEMPERATURE CHANGE DURING INITIATION OF THE END-TRIASSIC MASS EXTINCTION (Invited Presentation)

The end-Triassic mass extinction coincided with the eruption of the Central Atlantic Magmatic Province (CAMP), a large igneous province capable of providing a massive input of climate-altering volatile compounds to the atmosphere. The extinction mechanism is debated, but both short-term cooling from volcanically-sourced sulfur aerosols and longer-term warming from CAMP-related CO₂ emissions—essentially opposite hypotheses—are suggested triggers. The extinction interval is well-preserved in the uppermost Triassic strata of the Lilstock Formation, southwest United Kingdom, and marked in some areas by a notable deposit of stromatolitic carbonate known as the Cotham Marble (CM). The CM was deposited in the shallow Tethys Sea between the paleocontinents of Laurasia and Gondwana, though the specific paleoenvironment (e.g. open ocean vs. restricted basin/lagoon) is debated. Here, we report clumped-isotope paleothermometry from the CM microbialites, coupled with climate modeling and rare earth elemental abundances to reconstruct ocean temperature and geochemical conditions during the extinction interval. We find mild to warm ocean temperatures during the extinction interval and evidence for repeated temperature swings of 15ºC. Climate models suggest the temperature record is best interpreted as a signature of strong seasonality during the deposition of the CM. Thus, the results may constitute the oldest non-skeletal marine seasonal temperature record, to date. High-precision trace element data from weak leaching of carbonate reveal rare earth element (REE) spectra broadly similar to modern seawater, with positive La anomalies, supra-chondritic Y/Ho ratios, and mild light-to-heavy REE enrichment. We resolve no apparent evidence for cooling or initial warming across the 1-40kyr of the extinction event our record captures, implying that the initial onset of the biodiversity crisis may necessitate another mechanism.