Carboniferous- Middle Permian sedimentary- paleogeographic environment and source of the lithium- rich claystones in the Central Yunnan basin, SW China
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    Abstract:

    The Carboniferous- Middle Permian sedimentary sequences of the Central Yunnan basin, SW China, are rich in bauxite, coal, calcite, limestone, and other types of ore deposits associated with numerous lithium- rich claystones. Understanding the genesis of these ore deposits necessitates a comprehensive analysis of the spatial- temporal evolution of the sedimentary environments and the basin' s paleogeography. Systematic field investigations demonstrate that Carboniferous sedimentation in the Central Yunnan basin was dominated by terrigenous clastic and carbonate rocks deposited in a littoral tidal flat- lagoon environment. In contrast, the Lower- Middle Permian sedimentary rocks were mainly deposited in a lagoon- tidal flat- open platform environment. The Lower Carboniferous Datang Formation is characterized by carbonates with muddy shale interlayers, indicating deposition in a tidal flat environment. Lagoon deposition was restricted to areas adjacent to the Niushoushan paleo- uplift. The Middle Carboniferous Weining and Maping formations represent littoral- tidal flat deposits, sporadically exposed around this uplift. The Lower Permian Daoshitou Formation, composed of fine- grained terrigenous clastic rocks with minor limestone lenses, reflects deposition in a tidal flat- lagoon setting. This formation is particularly significant as it hosts the bauxite, coal ore deposits, and lithium- rich claystones. The Middle Permian Qixia and Maokou formations consist of algal clastic limestone, dolomitic leucoblastic bioclastic limestone, and medium- to coarse- grained dolomite, indicating an open- platform depositional environment. A distinct spatial pattern is observed in the thickness of the Datang and Daoshitou formations, with a pronounced thinning trend towards the south. This, coupled with a decrease in the number of coal and bauxite layers southward, suggests a gradual shallowing of seawater depth towards the south, bringing the deposits closer to their source area. Conversely, the Qixia and Maokou formations exhibit a widespread exposure in the north, with their thickness increasing northward. This observation is consistent with the SE- high and NW- low paleogeography of the Central Yunnan basin during the Early- Middle Permian, as evidenced by paleocurrent data. The Niushoushan paleo- uplift, a major source region of the Daoshitou Formation, played a pivotal role in shaping this paleogeographic setting. Geochemical data demonstrate that the Daoshitou Formation is rich in aluminum- and lithium- rich claystones. The concentrations of lithium and bauxite ore (Al2O3) are controlled by weathering processes in the source areas and sedimentary conditions. When Al2O3 content is less than 55% and the Al2O3/SiO2 ratio is less than 3, a positive correlation between lithium content and Al2O3 content is observed. This relationship becomes negative for other variation intervals. Regional geological data analysis demonstrates that the Niushoushan paleo- uplift mainly comprises Precambrian intermediate- mafic volcanic and sedimentary rocks. During the Early- Middle Permian, this region experienced a warm and humid environment. The continuous opening of the Paleo- Tethys during the Early Carboniferous to Middle Permian resulted in regional uplifting and erosion of the Paleo- uplift, exposing Precambrian volcanic rocks and related sedimentary rocks, leading to widespread volcanism. These eroded detritus and volcanic eruptions adjacent to the Niushoushan paleo- uplift are the important sources for the formation of bauxite ore deposits and lithium- rich claystones in the Central Yunnan basin.

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ZHANG Jiahui, YAN Zhen, XUE Chuandong, YU Liangjun, WEI Aiying, FU Changlei, WANG Wei, WANG Yu, ZHOU Honglin.2025. Carboniferous- Middle Permian sedimentary- paleogeographic environment and source of the lithium- rich claystones in the Central Yunnan basin, SW China[J]. Acta Geologica Sinica,99(4):1120-1133

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  • Online: April 27,2025