摘要： 桂西地区二叠系合山组铝土岩的沉积环境存在海相、陆相之争。通过对桂西二叠系铝土岩的区域调查及钻孔样品微量元素地球化学数据的分析,认为桂西二叠系铝土岩产出于陆相环境。从铝土岩分布情况看,桂西二叠纪各孤立碳酸盐岩台地上均广泛分布铝土岩沉积,该区域产出特征证明矿层是在碳酸盐岩台地全部暴露地表的环境下形成的。从铝土岩层与下伏茅口组灰岩的接触关系来看,铝土岩层底部存在茅口组灰岩砾石,在部分剖面尚见下伏茅口组灰岩中充填铝土岩等现象,说明铝土岩矿化过程直接于茅口组灰岩的古喀斯特面上完成。此外,在矿层中发现古植物根茎化石也是铝土岩形成于陆相环境的有力证据。从微量元素地球化学结果来看,来自铝土岩层样品的硼含量均小于10×10^-6,Sr/Ba值范围为0.29~1.61,平均值为0.92,Rb/K值范围为0.0011~0.0025,平均值为0.0017,以上指标结合V/Zr-Zr/Cu图解的判别,结果均指示铝土岩形成于陆相淡水环境。

关键词: 桂西, 合山组, 铝土岩, 沉积环境, 古盐度

Abstract: There exists a controversy about the sedimentary environment of the allites in the Permian Heshan Formation in western Guangxi: Land environment or marine environment? Based on the field investigation and geochemical data of samples from the Permian allites, we believed that the Permian allites in western Guangxi were deposited in the land environment. That the allites distributed continuously and widely on the isolated carbonate platforms in the Permian in western Guangxi indicated that the bausite ore beds were formed in an exposed carbonate platform environment. According to the contact between the allites and the carbonate substratum of the Maokou Formation, there existed carbonate gravels in the bottom of allites formation, and it could be seen that the allites filled the carbonate substratum in some sections, and this indicated that the bauxitization occured directly on the ancient karst surface. Additionally, the acient plant fossils in the bauxite ore beds also revealed the allites were formed in land environment. Combined with the V/Zr-Zr/Cu discriminant plot, the geochemical data of the allite samples, Boron contents lower than 10×10-6, Sr/Ba range of 0.291.61 with the mean of 0.92, Rb/K range of 0.00110.0025 with the mean of 0.0017, indicated that the allites in the Permian Heshan Formation in western Guangxi were formed in the land freshwater environment.

Key words: western Guangxi, Heshan Formation, allite, sedimentary environment, paleosalinity

中图分类号: 

• P588.24

• P611.2