Was a global Carnian Pluvial Event responsible for the origin of the dinosaurs?

MANCUSO, ADRIANA CECILIA; MUNDIL, ROLAND; IRMIS, RANDALL B.; WHITESIDE; BENAVENTE, CECILIA ANDREA

Congreso; EGU General Assembly 2019; 2019

EGU

The Late Triassic Period was a pivotal time in Earth history during a hothouse world with high atmospheric CO2,and included the origin of many animal groups that dominated ecosystems for the rest of the Mesozoic. One suddenclimate event during this time that has received renewed attention is the Carnian Pluvial Event (CPE) (orHumid Phase/Wet Intermezzo), which some recent authors suggest was responsible for the origin and early diversificationof dinosaurs. The CPE began during the middle Julian (>231 Ma), and is associated with warming,increased precipitation, perturbation of the carbon cycle, enhanced weathering, and disruption of the carbonatefactory. Most of this evidence comes from marine sections in the Tethys region, so the global extent of the CPEis poorly supported. Furthermore, precise and accurate absolute age constraints for key CPE sections are lacking.To help rectify this situation, we present new multiproxy paleoenvironmental evidence from Carnian lacustrinestrata in Argentina (45S paleolatitude) calibrated by a new high-precision U-Pb CA-TIMS zircon age from aninterbedded tuff. These data (sedimentology, clay mineralogy, carbon and oxygen stable isotopes from carbonatesand organic matter, and fossils) indicate that the middle Carnian portion of the section possessed particularlywarm and wet conditions associated with a dynamic carbon cycle, consistent with the effects and timing of theCPE. Furthermore, these strata also contain fossil evidence for the presence of early dinosaurs or their closest relatives.Nonetheless, the global evidence for dinosaur origins at the CPE remains weak given that all unambiguousdinosaur fossils either post-date the event or are poorly dated. Resolving these issues will require more detailedpaleoenvironmental proxy data from many sequences outside of the Tethys, and more precise geochronology forboth Tethyan marine successions and dinosaur-bearing strata worldwide.