A NEW TRIASSIC CLIMATE (δ18O) RECORD FROM CONODONT APATITE AND IMPLICATIONS FOR MAJOR BIO-EVENTS

We have established a new and comprehensive record of long-term climate change for the Triassic period. The record was determined from the oxygen isotope compositions of conodont apatite (δ¹⁸O_phos) using secondary ion mass spectrometry (SHRIMP II). Notably, this method permits spatially targeted and multiple in-situ spot (30μm) analyses of individual conodont specimens, as well as species-based comparisons, the latter being useful for discriminating taxon-specific effects (eg. biofacies). The δ¹⁸O_phos record was determined from 98 samples (>1600 spot analyses from >500 conodonts) from the western and central Tethys, which span the Early-Late Triassic. Our δ¹⁸O_phos record reveals that the Triassic climate was not as static or gradual as previously thought. There were three major, first-order negative shifts reflecting intense warming episodes, not only the well-known PTB-Early Triassic event, but also two large cycles of similar magnitude and duration during the late Carnian and late Norian. A series of alternating short-term cooling-warming cycles occurred throughout the Middle Triassic that decreased in magnitude reflecting an unstable but ameliorating climate. Three distinct short-term warming events occurred during the mid-late Anisian, early Ladinian, and latest Ladinian. In contrast, following each of the two major Late Triassic warming cycles, the Norian and Rhaetian experienced cooler (ie. mild) periods of sustained climate stability representing much more favourable climatic conditions. Notably, the five humid episodes recognized from the geological record are all associated with negative δ¹⁸O_phos (warming) events. Our δ¹⁸O_phos record thus provides a very new perspective on Triassic climate, which will also be discussed in the context of known geological and biological events.