Late Pliocene Monsoonal Rainfall Gradients in Western China Recorded by the Eolian Deposits From the Linxia Basin, NE Tibetan Plateau

Abstract

AbstractLoess and red clay sediments from the Chinese Loess Plateau (CLP) contain a wealth of information about variations in the Asian monsoon and the aridification history of the Asian interior. However, relatively little is known about late Pliocene palaeoenvironmental evolution and the variations in the gradients of monsoonal rainfall in the western part of the CLP, due to the poor exposure of pre‐Quaternary eolian deposits and uncertainties in the interpretation of paleoclimatic proxies in most parts of the region. To address these issues, we conducted a detailed rock magnetic investigation of newly drilled eolian sequences (spanning 3.7–2.4 Ma) from the Linxia Basin, NE Tibetan Plateau. Our results demonstrate that pedogenically formed fine magnetic grains are responsible for the magnetic enhancement of loess‐red clay sediments from the basin. Spatially, a clear decrease in magnetic susceptibility and its frequency dependence is observed between the central and western CLP, indicating that the East Asian summer monsoon already exerted a major influence on the amount and distribution of late Pliocene rainfall in the Linxia Basin. After evaluating the validity of magneto‐climofunctions, we attempt to reconstruct late Pliocene‐early Pleistocene monsoonal precipitation in the NE margin of the Tibetan Plateau. The results demonstrate that the difference in late Pliocene monsoonal rainfall between the study area and Chaona in the central CLP was about 300–400 mm. This value is higher than that of the present day, indicating a steepened gradient in monsoonal rainfall between the central and western CLP during the late Pliocene.