This paper presents detrital modes, clay and carbonate cements and major and trace element contents of the sandstones from the lower Xiaganchaigou formation deposited during the Eocene/Oligocene transition in the Lenghu tectonic belt on the northern margin of the Qaidam Basin, NW Qinghai–Tibetan plateau. Our results show that the sandstones are mainly lithic feldspathic, with clay content varying from 4.1 to 42.5 vol. % (average 13.7 vol. %). These sandstones have low contents of Na₂O, MgO, Al₂O₃, K₂O, CaO and TiO₂, with the average contents of 2.14 wt%, 0.78 wt%, 7.96 wt%, 2.11 wt%, 6.14 wt% and 0.15 wt%, respectively. The total content of major elements is < 30 wt%, indicating that the pore water was in an alkaline environment with high pressure, so that the decarboxylation reaction of the organic matter took place to generate a large amount of carbon dioxide with a loss of ¹³C. Consequently, the δ¹³C of the carbonate cement is negatively biased to − 6.4‰; the deep high temperature environment and the external fresh water leaching make the δ¹⁸O value of the carbonate cement gradually lose, reaching − 13.19‰, according to its precipitation temperature (78–108 °C) and pore water salinity (104–110), it is judged that carbonate cement is mainly formed in the middle diagenetic stage and early diagenetic stage. The rare earth elements are mainly authigenic by the results of ∑REE and Y/Ho, and the deposition characteristics of trace elements such as Zn, Th, U, Ni, Co, Cr, Sr/Cu, Ce_anom, Ce/La, ∑REE, Eu/Eu*, La/Yb, V/(V + Ni) and the transformation of later diagenesis, combining the characteristic of the global climate and the influence of uplifting of the Qinghai–Tibetan Plateau, indicate that the lower Xiaganchaigou formation was in a dry, cold and anoxic reducing environment.

中文翻译：

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柴达木盆地冷湖构造带始新世-渐新世过渡期下关断沟组下部成岩作用及沉积环境

本文介绍了西北西北部柴达木盆地北缘冷湖构造带始新世-渐新世过渡期沉积的下关断沟组下层砂岩的碎屑模式，粘土和碳酸盐胶结物以及主要和微量元素含量。 。我们的研究结果表明，砂岩主要为岩性长石质，粘土含量为4.1至42.5 vol。％（平均13.7体积％）。这些砂岩的Na ₂ O，MgO，Al ₂ O ₃，K ₂ O，CaO和TiO ₂含量低的平均含量分别为2.14 wt％，0.78 wt％，7.96 wt％，2.11 wt％，6.14 wt％和0.15 wt％。主要元素的总含量<30 wt％，表明孔隙水处于高压的碱性环境中，因此发生了有机物的脱羧反应，生成大量二氧化碳，损失了¹³ C.因此，δ ¹³碳酸盐水泥的C被负偏置到- 6.4‰; 深的高温环境和外部淡水淋滤使所述δ ¹⁸碳酸盐水泥的O值逐渐下降，达到− 13.19‰，根据其降水温度（78–108°C）和孔隙水盐度（104–110），判断碳酸盐水泥主要形成于中成岩阶段。和成岩早期。稀土元素主要是通过∑REE和Y / Ho的结果而自生，以及微量元素如Zn，Th，U，Ni，Co，Cr，Sr / Cu，Ce _anom，Ce / La， ∑REE，Eu / Eu *，La / Yb，V /（V + Ni）以及后期成岩作用的转变，结合全球气候特征和青藏高原的隆升影响，表明下霞差沟地层处于干燥，寒冷和缺氧的还原环境中。