The average thickness of Paleogene sandstones reaches about 3000–4000 m at the northern margin of the Qaidam Basin. However, the provenance and sedimentary environment of these sandstones are uncertain; thus, more comprehensive research is needed. Integrated research is conducted on the provenance and weathering process based on petrographic characteristics, clay minerals, and geochemical compositions of sandstones in the center of the northern Qaidam Basin. The results of lithofacies analysis show that the Paleogene sandstones were mainly derived from an active continental magmatic arc, subduction accretion, or a fold-thrust belt. The average illite content in the Paleogene clay minerals is more than 50%, followed by chlorite and smectite, which reflect climatic and environmental characteristics that were arid to semi-arid, whereas the characteristics of carbon–oxygen isotopes reveal a mainly freshwater sedimentary environment. The corrected chemical index of alteration (CIA_corr) is between 56.3 and 75.7, with an average value of 66.5. These results indicate that the provenance of the Paleogene sandstones in the center of the northern Qaidam Basin mainly formed under cold and dry climatic conditions and experienced limited chemical weathering with a small amount that underwent intermediate chemical weathering under warm and humid conditions.

中文翻译：

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柴达木盆地北缘中心古近系砂岩中粘土矿物和元素的地球化学意义

柴达木盆地北缘古近纪砂岩的平均厚度约为3000-4000 m。但是，这些砂岩的物源和沉积环境尚不确定。因此，需要更全面的研究。根据柴达木盆地北部中部的岩石学特征，粘土矿物和砂岩的地球化学组成，对物源和风化过程进行了综合研究。岩相分析结果表明，古近系砂岩主要来自活跃的大陆岩浆弧，俯冲增生或褶皱冲断带。古近纪粘土矿物中的伊利石平均含量超过50％，其次是绿泥石和绿土，它们反映了干旱至半干旱的气候和环境特征，而碳氧同位素的特征则揭示出主要是淡水沉积环境。校正后的化学变化指数（CIA_corr）在56.3和75.7之间，平均值为66.5。这些结果表明，柴达木盆地北部中部的古近纪砂岩的物源主要是在寒冷和干燥的气候条件下形成的，并且经历了有限的化学风化作用，少量经历了在温暖和潮湿条件下的中等化学风化作用。