Multistratigraphic Constraints on the Nw Tethyan “carnian Crisis”

The “Carnian Crisis” is documented in basinal, shallow-marine and epicontinental northwestern Tethyan facies areas by, successively, (1) a demise of carbonate platforms and reefs in the Julian 1/IIc, (2) a major faunal and floral turnover in the Late Julian and (3) a significant extinction event affecting conodonts and ammonoids at the Julian/Tuvalian boundary. Based on the study of 19 successions from the NW Tethys, the presence of short-lived ammonoid and conodont taxa and the sudden absence of reef-derived debris in basinal and shallow-marine successions document a strict synchroneity in latest Julian 1 of a carbonate productivity crisis. Ophos values measured on conodont apatite display a major negative shift of 2.0 ‰ [V-SMOW] in the latest Julian 1 and Julian 2 indicating climate warming and a change in seawater salinity. This interpretation fits with changes in lithofacies and argues for humidification and enhanced freshwater runoff (sensu Simms and Ruffell, 1989), resulting in higher nutrient levels as the main factors of both reef disease and decline of nektonic biodiversity in late Early Carnian time.