East Asian hydroclimate responses to the Eocene-Oligocene transition in the Weihe Basin, central China

Abstract

The Eocene-Oligocene transition (EOT) at ∼34 Ma marked a significant global cooling on Earth when the ice cover in the Antarctic was formed. How the regional hydroclimate responded to this global cooling event has been extensively investigated, but the specific processes in the Asian monsoon dominated regions are still elusive, due to the lack of independent and detailed timescales. Moreover, previous sedimentary records are mainly from the Asian interior and the influence of tectonic deformation/uplifts in northeastern Tibetan Plateau on the deposit records has not been effectively separated. Here, we present a high-resolution hydroclimate record from a fluvial-lacustrine sequence in the Weihe Basin, central China, which is dated from ∼34.9 to 31.5 Ma by a high-resolution magnetostratigraphy with age controls of mammal fossil assemblages and apatite fission track (AFT) chronometry. This record shows a remarkable hydroclimatic shift occurred at ∼33.7 Ma, as manifested by a sedimentary environment change from lakeshore to lake-delta. The associated significant changes in sediment grain size and magnetic susceptibility exhibit responses of regional drying to the EOT and the Early Oligocene Glacial Maximum (EOGM). In addition, spectral analyses of the time series of paleoenvironmental proxies reveal that the hydroclimate also varied at orbital frequencies with relatively persistent eccentricity cycles (∼100 kyr), accompanied by precession (∼20 kyr) and obliquity (∼ 40 kyr) cycles after the formation of the Antarctic ice sheet at ∼33.2 Ma. Our results suggest that the monsoon-like paleoclimate variations in the mid-latitude northern Hemisphere during the EOT were partly modulated by high-latitude temperature and insolation variations.