黄土高原风尘沉积的物质来源研究:回顾与展望

黄土高原风尘沉积是青藏高原构造隆升和东亚季风系统共同影响下的产物。由于风尘物质的来源变化,不仅反映了亚洲内陆的干旱化过程,而且同过去大气环流格局变迁关系密切,因而,风尘物质来源的示踪一直是黄土研究的热点问题之一。文章首先回顾黄土来源的示踪方法、黄土物质的可能源区以及黄土物源在构造和轨道时间尺度上的变化特征3个方面取得的研究进展,然后探讨目前物源研究存在的问题及未来的研究展望。

STUDY ON PROVENANCE OF EOLIAN DUST DEPOSITS ON THE CHINESE LOESS PLATEAU: RETROSPECTS AND PROSPECTS

Eolian deposits on the Chinese Loess Plateau are considered as the products of coupled interactions between Tibet uplift and Asian monsoon systems.Changes in the provenance of Chinese loess not only reflect the Asian inland drying history but also link to fluctuations of the past atmospheric circulations.Thus,tracing the sources of eolian dust is one of the hotspots of current loess research.In this study,we briefly review previous provenance studies in the following three aspects:(1)provenance tracers such as elemental ratios,isotopic compositions,ESR signal intensity,and crystallinity of quartz;(2)potential sources of loess deposits on the Chinese Loess Plateau,including Gobi and sandy deserts in Northern China and Southern Mongolia;and(3)fluctuations of the loess provenance at tectonic to orbital time scales.Both meteorological observation data and simulation results indicate that over the past four decades Asian dust originates mainly from three major source areas including the Gobi desert in Southern Mongolia,deserts in Northern China(mainly Badain Jaran and Tengger deserts),and Taklamakan Desert in Western China.However,relative contribution of the three major dust sources to the loess accumulation on the Chinese Loess Plateau is still controversial,particularly regarding the dust source in Western China(e.g.,Taklamakan Desert and Qaidam Basin).Moreover,extant provenance studies have yielded differing viewpoints on whether the dust provenances have experienced significant shifts or are more uniform at orbital to tectonic time scales.Possible origin for these discrepancies is because some of these provenance tracers might be influenced by physical and chemical weathering during dust transportation and after dust deposition,and therefore cannot effectively differentiate the potential dust sources.To better determine the dominant sources of Chinese loess and evaluate provenance variations of Late Cenozoic loess deposits,further remarks on the loess provenance study are listed as follows:(1)systematic investigation on the dust source areas including the surrounding high-altitude terrains;(2)looking for new provenance tracers;(3)evaluating the potential sources of fine-and coarse-grained dust deposits separately;and(4)comparison between eolian dust depositions on the land and in the ocean.