青海湖种羊场风成沉积的常量元素组成及其化学风化指示

Major Elements of the Eolian Deposits at Zhongyangchang Site in the Qinghai Lake and Their Implication on Chemical Weathering Change

青海湖区是研究亚洲季风和西风环流强度变化和相互作用的良好区域。与青海湖湖泊钻孔沉积物一样,青海湖岸边广泛堆积的陆相风成沉积独立地记录了青海湖区晚第四纪以来的环境演变。过去对青海湖风成沉积的元素地球化学特征虽有过一些研究,但对于这套风成沉积的化学风化研究相当薄弱。通过对青海湖东岸种羊场剖面晚第四纪风成沉积的常量元素组成及主要的化学风化指标进行研究,结果表明：1）化学风化指标CIA（化学蚀变指数）、CIW（化学风化指数）、K2O/Na2O和Fe2O3/Mg O比值均反映了种羊场风成沉积经历了早期化学风化强度弱、中期强和晚期再度变弱的变化特征;2）在距今~5 ka时,风化指标显示化学风化作用最强,可能记录了青海湖区暖湿的气候特征;3）种羊场风成沉积的Fe2O3/Mg O比值与!fd%（频率磁化率的百分比）呈显著线性正相关（相关系数R2为0.939）,指示在化学风化过程中Fe元素的富集对于磁化率增强具有重要贡献。

Qinghai cluding East Asian sediments from the Lake is a pivotal region for researching the interactions between Asian monsoons （in- monsoon and Indian monsoon） and the Westerlies. Independent to the drilling core Qinghai Lake ,the eolian deposits around the Qinghai Lake are another environmentalarchive in the Qinghai Lake region. Continuous eolian deposition in the Qinghai Lake region probably star- ted at 16 - 14 ka. Though a few studies on the element geochemistry of the eolian deposits in the Qinghai Lake region have been investigated, the study of the chemical weathering change conducted on eolian de- posits is very limited. This study investigated the major elemental compositions of the eolian deposits at Zhongyangchang site （ZYC section） in the Qinghai Lake region and their implication on chemical weath- ering change. The following conclusions were drawn ： （ 1 ） Chemical weathering indexes CIA （ chemical in- dex of alteration） ,CIW（ chemical index of weathering） ,K/O/Na2O and Fe2O3/MgO mole ratios indicate that the Holocene eolian deposits at ZYC section experienced weak chemical weathering in the early stage,strong chemical weathering in the middle stage and weak again in the late stage. （2） about 5 ka ago, all indexes recorded the strongest chemical weathering, showing that the climate of this period was probably warm and wet, consistent with the high lake level in the Hurleg Lake occurred at 5.0 - 4.7 ka in the Qaidam basin;（3 ） Fe2O3/MgO ratio is highly positively correlated with χfd% （frequency-dependent mass magnetic susceptibility as a percentage）with a linear correlation coefficient R2 of 0. 939 for the eoli- an deposits at ZYC section, indicating that the enrichment of element Fe significantly contributes to the magnetic susceptibility enhancement during the process of chemical weathering.