Sedimentary record of climate change across the Eocene/Oligocene transition from the Qaidam Basin, northeastern Tibetan Plateau

Abstract

The Eocene/Oligocene transition (EOT) was marked by a major environmental reorganization accompanied by an abrupt shift of the Earth system from “greenhouse” to “icehouse” conditions, which is well documented in marine sedimentary records. Although there are an increasing number of terrestrial records documenting this major climatic reorganization, high-resolution sedimentologic and petrographic evidence from terrestrial contexts is sparse, and the processes driving the EOT which affected the formation of continental detrital sediments are unclear. Here we present evidence from lithofacies, lithology, sediment color, and sediment grain size from a section in the northern part of the NE Tibetan Plateau (Tibetan Plateau), which spans the EOT. The results indicate that major changes in the grain size (coarsening), chromaticity a* (redness increasing), thick gypsum layers (disappearance), structural maturity (decreasing roundness and sorting), sediment compositional maturity (increasing content of lithic, feldspar and mafic minerals) of silt and sandstone occurred at ~33.8 Ma, which were considered to be a response to the EOT. The synchronous changes in sedimentological and petrological characteristics and weathering proxies in the Qaidam Basin (Qaidam Basin) and neighboring basins suggest that the climate-forced weakening of weathering and erosion may have been the direct cause of those proxy changes the direct cause of those proxy change. Global cooling is speculated to have been the first-order driving factor in regulating climatic evolution and weathering responses in the Qaidam Basin and even the Asian interior at the EOT. A conceptual model is presented which summarizes the mechanisms responsible for the observed changes in sedimentary characteristics across the EOT.