Late Cretaceous–Paleogene Indian monsoon climate vis-à-vis movement of the Indian plate, and the birth of the South Asian Monsoon.

After India separated from Gondwana, its 9000 km northward voyage from the Southern Hemisphere to its modern position joined with Eurasia took 160 million years. During that journey, India experienced a range of climatic conditions due to secular climate variations and its changing latitudinal position. Documenting India's climate during its trans-equatorial journey allows us to sample climate across the low latitudes, at a time when global temperatures were exceptionally high, such as we might experience in the future. Here, we reconstruct, quantitatively, the palaeoclimate of India during its voyage, focussing on the latest Maastrichtian–earliest Danian, late Paleocene, early Eocene and late Oligocene timeslices. We exploit the relationship between fossil leaf form and climate and use the Climate-Leaf Analysis Multivariate Program to reconstruct 24 individual palaeoclimate parameters, while fossil leaf traits also allow us to identify different monsoon types. We find that throughout the Paleogene India persistently experienced a monsoon climate similar to that of modern Indonesia-Australia; a monsoon system that exists today primarily as a function of seasonal trans-equatorial migrations of the Inter-tropical Convergence Zone (ITCZ). The reconstructed near-equatorial thermal regime of India was cooler, and showed a greater seasonal temperature variation than at similar latitudes today, suggesting a wider seasonal latitudinal migration of the ITCZ throughout the Paleogene. Leaf traits showing adaptation to the South Asia Monsoon only developed after the end of the Paleogene. [Display omitted] • Fossil leaf form is used to reconstruct Paleogene climate as India moved northwards. • An Indonesia-Australia type ITCZ monsoon dominated until the late Oligocene. • The first signs of a South Asia Monsoon (SAM) appear in the late Oligocene. • SAM onset due to mechanical forcing of air flow by the rapidly rising Himalaya. • SAM origins pre-date Tibetan Plateau formation. [ABSTRACT FROM AUTHOR]