CONODONTS AS PALEOTHERMOMETERS: HOW HOT WERE EARLY TRIASSIC OCEANS?

The end-Permian event (~252.6 million years ago) was the largest biotic crisis of the Phanerozoic. The ultimate cause of this mass extinction is still debated, but extensive volcanic degassing from the Siberian Traps Large Igneous Province and induced climatic and environmental changes probably triggered both marine and terrestrial extinctions. The tempo and pattern of the subsequent biotic recovery during the Early Triassic has been the subject of several controversies.

Biodiversity dynamics and the carbon isotope record show large fluctuations during the Early Triassic and these variances have been interpreted as evidence for climate instabilities. This was confirmed recently by a few studies (e.g. Sun et al. 2012, Romano et al. 2013) that presented high-resolution records of Early Triassic seawater paleotemperatures based on oxygen isotope compositions of conodont elements. In particular we observed an ocean warming at the end of the Smithian, followed by a cooling in the early Spathian. This global warming was presumably a major cause of the end-Smithian extinction and the cooling presumably correlates the early Spathian rediversification.

We performed some new SHRIMP in situ measurements of δ¹⁸O ratios on conodont elements from the Smithian-Spathian boundary. In the light of our new high-resolution results, we review the timing of these temperature fluctuations and their implications for our understanding of the relationship between climate and biodiversity.