Long-term cycles of Triassic climate change: a new δ18O record from conodont apatite

A new oxygen isotope (δ18O) record derived from conodont apatite reveals variable long-term climate trends throughout the Triassic period. This record shows several major, first order, negative shifts reflecting intense warming episodes, not only the well-known extreme PTB–Early Triassic event ( ∼ 5 ‰ ), but also two large cycles of similar magnitude (∼1.5, ∼ 1.7 ‰ ) and duration (∼7 Myrs) during the late Carnian and late Norian. Between the PTB–Early Triassic and Carnian major episodes, three rapid shorter-term warming events of decreasing magnitude punctuate the mid–late Anisian, early Ladinian, and latest Ladinian, with distinct cooler (i.e. favourable) intervals characterising the early Anisian and early Carnian, indicating a fluctuating but ameliorating Middle Triassic climate trend. Two long periods of sustained cooler conditions occurred during the Late Triassic, for much of the Norian and Rhaetian. The five humid events previously recognised from the geological record, including the Carnian Pluvial Episode, are associated with the low δ18O warming phases. The magnitudes of these first order warming cycles, together with widespread geological and palaeontological evidence, suggest they were at least Tethyan-wide events.