Evolving sources of eolian detritus on the Chinese Loess Plateau since early Miocene: Tectonic and climatic controls

The thick deposits of eolian dust on the Chinese Loess Plateau provide a rare opportunity to explore the past changes of surface processes in response to climatic and tectonic oscillations. Here we report a 22 Ma-long Nd and Sr isotopic records of the eolian sources. Decreasing epsilon(Nd) values and increasing Sr-86/Sr-87 ratios of the eolian deposits has been observed from early Miocene to about 7 Ma, which indicates growing material contribution from Qilian Mountains relative to the Gobi Altay Mountains. The source shift during 22-7 Ma is interpreted to reflect the erosional response of the Qilian Mountains to its surface uplift. Between 7 Ma and 12 Ma, the results show relative constant Nd and Sr isotopic compositions of the eolian deposits, and thus suggest a constant source contribution between Qilian Mountains and Gobi Altay Mountains. Synchronized uplift of the two mountain ranges during this period may explain the constant ratio of source contribution. Since 1.2 Ma, Nd and Sr isotopic records indicate that the relative debris input from Qilian Mountains drops rapidly. As large-scale topographic changes would not be expected in such a short time period, the source shift since 1.2 Ma might be by the differing erosional responses in Qilian Mountains and Gobi Altay Mountains to the development of full glacial climate after the middle Pleistocene transition. This work shows that combined Nd and Sr isotopic signatures of the dust records are valuable proxies to monitoring past surface processes on the million years time scale. (C) 2013 Elsevier B.V. All rights reserved.