Abstract
Cenozoic climate cooling at the advent of the Eocene-Oligocene transition (EOT), ~33.7 Ma ago, was stamped in the ocean by a series of climatic events albeit the impact of this global climatic transition on terrestrial environments is still fragmentary. Yet archival constraints on Late Eocene atmospheric circulation are scarce in (tropical) monsoonal Asia, and the paucity of terrestrial records hampers a meaningful comparison of the long-term climatic trends between oceanic and continental realms. Here we report new sedimentological data from the Jianchuan basin (SE Tibet) arguing for wetter climatic conditions in monsoonal Asia at ~35.5 Ma almost coevally to the aridification recognized northwards in the Xining basin. We show that the occurrence of flash-flood events in semi-arid to sub-humid palustrine-sublacustrine settings preceded the development of coal-bearing deposits in swampy-like environments, thus paving the way to a more humid climate in SE Tibet ahead from the EOT. We suggest that this moisture redistribution possibly reflects more northern and intensified ITCZ-induced tropical rainfall in monsoonal Asia around 35.5 Ma, in accordance with recent sea-surface temperature reconstructions from equatorial oceanic records. Our findings thus highlight an important period of climatic upheaval in terrestrial Asian environments ~2–4 millions years prior to the EOT.
Highlights
Cenozoic climate cooling at the advent of the Eocene-Oligocene transition (EOT), ~33.7 Ma ago, was stamped in the ocean by a series of climatic events albeit the impact of this global climatic transition on terrestrial environments is still fragmentary
Our results reveal a prominent environmental shift from palustrine-lacustrine sedimentary signatures to more humid conditions around ~35.5 Ma, as revealed by regular occurrences of coal-bearing deposits (Shuanghe Fm.), providing regional lines of evidence that SE Tibet experienced a marked climatic change associated with amplified precipitation during the Late Eocene
This possibly includes a decline of the dry season duration, but more likely enhanced annual precipitation and a waning of the continentality in SE Tibet around ~35.5 Ma
Summary
Cenozoic climate cooling at the advent of the Eocene-Oligocene transition (EOT), ~33.7 Ma ago, was stamped in the ocean by a series of climatic events albeit the impact of this global climatic transition on terrestrial environments is still fragmentary. We show that the occurrence of flash-flood events in semi-arid to sub-humid palustrine-sublacustrine settings preceded the development of coal-bearing deposits in swampylike environments, paving the way to a more humid climate in SE Tibet ahead from the EOT We suggest that this moisture redistribution possibly reflects more northern and intensified ITCZ-induced tropical rainfall in monsoonal Asia around 35.5 Ma, in accordance with recent sea-surface temperature reconstructions from equatorial oceanic records. The paucity of paleoenvironmental data in the tropical latitude zone, especially from well-dated terrestrial records, hampers the evaluation of the response of continental settings to global climatic change during the LED, much needed for the understanding (and modelling) of processes leading to the transition from greenhouse to icehouse conditions. We focus on the sections in the eastern part of the Jianchuan basin, with a particular emphasis on the Jiuziyan and Shuanghe Fms. deposited between ~37 and 35 Ma
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