Discovery of One-and-a-Half Million Yearlong Aridity in the Tibetan Plateau Eocene Red Clays

Over the past five years, J.-P. Valet actively collaborated with the authors on studying long-term climate variations recorded in Chinese red clay deposits. Notably, our joint research identified the 1.2 Myr band of Earth-Mars obliquity modulation in the Late Miocene. Building on this foundation, we extend our investigation to red clay sequences in Tibet, employing magnetostratigraphy and rock-magnetic analyses to date the sections and extract paleoclimate signals influenced by orbital parameters.

The Eocene epoch witnessed significant global climate cooling and aridification, particularly near the Tibetan Plateau. Previously, the aridification was attributed primarily to the plateau’s uplift. However, recent studies suggest that global climate trends played a more substantial role. Here, we present new paleoclimate data from the Altun Shan red clay sequence, deposited between 40 and 50 Ma at the northeastern edge of the Tibetan Plateau. By constructing an age model using a synthesis of magnetostratigraphy and cyclostratigraphy, we show that variations in magnetic susceptibility in the Altun Shan sequence are linked to eccentricity cycles. The ~100-kyr short eccentricity cycle can be compared to marine climate proxy records, with 405-kyr eccentricity and 173-kyr obliquity cycles modulating the record amplitudes. The amplitude of the short eccentricity cycles decreased starting at the onset of global cooling at 49.1 Ma. Furthermore, we demonstrate that the aridification event in Altun Shan aligns with several key climate records: a cooling interval in the global oxygen isotope record, a sea surface temperature drop on the east Tasmanian Plateau, and increased aridity in Central Asian sedimentary basins. The middle Eocene aridity and cooling peaked between 45.5 and 44 Ma, marking a critical phase in the interplay between orbital forcing and global climate trends.