Lithology description of a 400 m-thick Paleocene strata borehole in the Xiaojinggu area, Yunnan

The most complete Early Cenozoic strata in the Simao Basin are located in Xiaojinggu Town, Jinggu County, which mainly includes the sedimentary strata of the Mengyejing Formation, the Denghei Formation and the Mengla Formation. Due to the tectonic uplifting of the mountain in the late Cenozoic, the syncline structure caused the top of the Mengyejing Formation, the Denghei Formation and the Mengla Formation to be exposed to the surface. However, a complete sedimentary profile containing the middle and lower part of the Mengyejing Formation could not be obtained due to vegetation cover and village construction. The chronological study of sedimentary strata in the Simao Basin is mainly concentrated in the Mengyejing Formation with potassium salt. However, there still has significant controversy about the deposition time of this group at this stage. Recently, a continuous and complete high-resolution sequence (361.86 m in thickness) of the Mengyejing Formation was obtained through the continuous drilling. Among them, the Mengyejing Formation (0-353.3 m) is mainly a set of purple-red muddy silt and mudstone combination, while the underlying Mangang Formation (353.3-361.86 m) is a set of gray-white sandstone.