Climatic oscillations at the onset of the Mesozoic inferred from palynological records from the North Indian Margin

The beginning of the Mesozoic, the Early Triassic, is characterized by several ecological perturbations following the end-Permian mass extinction. They are reflected in multiple C-isotope excursions coupled with climatic changes. Here we present palynological data from two accurately dated sections from the North Indian Margin (Pakistan and South Tibet). The climate of the Early Triassic was controlled by persistent monsoon circulation. The spore/pollen ratios, used as a proxy for humidity changes, indicate several significant climatic changes coinciding with C-isotope excursions. Comparison with published climate model simulations reveals that the climatic shifts were induced by orbital forcing and probably represent eccentricity cycles. Humidity peaks indicate an insolation forced shift of the intertropical convergence zone towards the North Indian Margin. Comparison with palynological data from Norway and other proxies reveal that the profound climatic change from humid to drier climate across the Smithian-Spathian boundary represents a global event, which affected southern and northern mid-latitudes and coincided with major ammonoid and conodont extinction events. This implies that increased greenhouse gas concentrations owing to recurring volcanic pulses increased the climate system sensitivity, resulting in climatic changes in distant parts of the world. Our data strongly support a link between C-isotope excursions, climatic changes and biotic responses.