Through core observation, thin section identification, and X-ray diffraction mineral analysis, the rock types and characteristics, and the genesis were studied. The results show that the core section of Liujiagou Formation develops grayish purple siltstone, rudaceous mixed rock and black mudstone. The siltstone was mainly composed of quartz, rock debris, feldspar, micrite calcite, and matrix, with a matrix-supported fabric, and developed turbidite sedimentary characteristics such as groove casts, graded bedding, flame structures, convolute bedding, and Bouma sequences, identifying it as turbidite. The mixed rock contained a large amount of gravel intraclast and interstitial material, with the latter composed of terrigenous clastic particles, intraclasts, and matrix. It exhibited sedimentary characteristics such as muddy tear-shaped clasts, matrix-supported structure, randomly oriented particles, and abrupt contact with the overlying and underlying mudstones, suggesting it was debris flow deposition. The study suggests that the Mianlue Ocean during the Early Triassic was not completely closed and had a marine transgression impact on the southwestern margin of the Erdos Basin, forming mixed rock strata. Lagoon sediments developed in the Zhengning area, with slopes present, and gravity flow sediments dominated by debris flow-turbidity current were developed at the place of Well C3.

The kaolinite claystone in the coal-bearing strata is a characteristic coal associated mineral resource in China, with various types of genesis, which can provide geological significance such as stratigraphy, chronology or tectonic geology. A set of thick-bedded grayish-white kaolinite claystone is developed in the coal-bearing strata of Shanxi Formation, Longdong area, Ordos Basin. The mineral composition and rock type were identified by core observation, thin section identification, scanning electron microscope analysis, X-ray diffraction (XRD) analysis and major element analysis. And the genetic type was preliminarily identified. The results show that the gray-white kaolinite claystone is mainly composed of clay minerals (74.96% on average), followed by quartz (14.28% on average) and siderite (10.46% on average). The clay minerals contained are dominated by kaolinite (76.2% on average) which is mostly cryptocrystalline aggregates. Quartz is mostly microcrystalline. And siderite is mostly lumped, oolitic, and disseminated. It can be further divided into three categories: gray-white siderite-bearing kaolinite claystone, gray-white sideritic kaolinite claystone and gray-white kaolinite claystone. The Hinckley index (Hi) of the grayish-white kaolinite claystone is low (0.25 on average), reflecting the genesis of redeposition after continental transport. The peak half height width (FWHM) of peak (001) is 0.269~0.567, and the calculated crystallinity ranges from 1.68 to 3.23, which is low overall, reflecting the the genesis of redeposition after continental transport or the genesis of redeposition after continental transport genesis of volcanic material alteration type. The ratio of major elements SiO₂/Al₂O₃ of is 2.02, which is characterized by high SiO₂, high Al₂O₃, high TFe₂O₃, and very low TiO₂, K₂O, MgO, CaO, and Na₂O, reflecting that it is not of volcanic ash alteration. The distribution of major elements contents is different from that of weathering residual sedimentary rocks. It is believed that the grayish white kaolinite claystone is formed by transport and redeposition after weathering, and belongs to the sedimentary genesis type. The high chemical alteration index (CIA) reflects the high intensity of chemical weathering and the tropical climate conditions in the sediment source areas of the rocks at the time of formation. The development of grayish white kaolinite claystone reflects the presence of tectonic activities in the late depositional stage of the Shanxi Formation and the transformation of the humid and hot climate in the source area of Longdong region, which can be used as a marker layer for the contrasting division of small layers and has geological significance of event stratigraphy. The development of siderite also provides evidence for the development of weakly reducing environment of delta front-shallow lake deposition in the study area.