柴达木西部南翼山构造地表混积岩岩石学特征及沉积环境讨论

南翼山构造地表狮子沟组发育混积岩，作为一种特殊类型的沉积岩，其研究具有一定的实际意义和科学价值。本文在野外观察和镜下鉴定的基础上，对南翼山混积岩样品进行了X衍射、主微量元素及碳氧同位素测试，分析了混积岩的岩石学特征，考虑到其成分和成因的复杂性，通过数据分析排除了多种干扰因素，最后利用有效指标综合判断了其沉积环境。结果显示：南翼山构造地表混积岩中陆源碎屑平均含量为58.7%，碳酸盐矿物含量为31.0%，属于碳酸盐质陆源碎屑岩，主要为钙质泥岩，其中碎屑矿物以细粉砂级石英为主，碳酸盐矿物主要为泥晶方解石，黏土矿物组合为伊利石和有序伊蒙混层，且三者呈均匀混合的特征。数据分析表明Ca、Na、Mn、Sr、Ba等元素主要来源于自生矿物，稀土元素及碳氧同位素组成未受成岩作用影响，可以作为判断沉积时水体盐度和氧化还原条件的指标。根据Sr/Cu比值和K2 O/Al 2O3比值，结合黏土矿物组合及伊利石结晶度和化学指数，判断地表混积岩沉积时为寒冷干旱的气候条件；Sr/Ba比值和Z值表明古水体介质为咸水环境；U/Th比值、自生U含量和Ce轻微负异常等指标综合判定其形成于弱氧化环境。以上研究表明，南翼山构造地表混积岩主要为陆源碎屑和碳酸盐矿物均匀混合的钙质泥岩，形成于寒冷干旱气候条件下的弱氧化咸水湖泊环境中。

Petrological Characteristics and Sedimentary Environment of the Surface Mixed Rocks in Nanyishan Structure, Western Qaidam Basin

Mixed rocks were developed in the Shizigou Formation of Nanyishan Structure surface. As a special type of the sedimentary rocks, its research has some practical significance and scientific value. Based on field observation and microscopic identification, this paper analyzed petrological characteristics of the mixed rock in Nanyishan using X- ray diffraction, major and trace elements, carbon and oxygen isotope test of mixed rock. Considering the complexity of compositions and genesis, this paper employed the effective indicators to determine the sedimentary environment plus excluding a variety of interference factors through data analysis. The results show that the average contents of terrigenous clastics and carbonate minerals in the mixed rocks are 58.7% and 31.0%, respectively, implying that the mixed rocks belong to carbonatic terrigenous clastic rock. Among them, the terrigenous clastic rock is dominantly calcareous mudstones, with detrital minerals consisting mainly of fine silt grade quartz; the carbonate minerals are mainly micritic calcite and clay minerals assemblages are illite and ordered illite/smectite mixed layer; and above three rokcs are mixed homogeneously. Data analysis shows that elements (such as Ca, Na, Mn, Sr, Ba et al.) mainly derived from authigenic minerals. REE, carbon and oxygen isotopic compositions, which were not affected by diagenesis, can be used to determine the salinity and redox conditions of waters during deposition. Combined with assemblage of clay minerals, crystallinity of illite, and chemical index, Sr/Cu and K2O/Al2O3 ratios suggest a cold and arid climate for the depositional period of the mixed rocks; Sr/Ba ratio and Z value indicate a salt water environment; and U/Th ratio, authigenic U and Ce negative anomaly synthetically show a weak oxidizing environment. The results above show that the mixed rocks in Nanyishan are dominantly calcareous mudstones consisting of terrigenous clastic and carbonate minerals, which formed in weak oxidizing saline lacustrine basin under the conditions of cold and dry climate.