It is the first time that the super abnormal enrichment of lithium has been reported in the claystone at the bottom of the Middle-Late Triassic Xujiahe Formation in the Zhenba area, located on the northern margin of the Yangtze plate. The claystone, which contains Li₂O ranging from 0.08% to 0.11% (up to 0.22%), develops in the parallel unconformity interface of Guanling Formation (T₂g)/Xujiahe Formation (T₃x), representing ancient weathering crust sediments. The Li₂O content exceeds the boundary grade (0.06%) of this type of deposit. To further understand the petrological characteristics, mineral composition, and petrogenesis of the boundary claystone, this paper aims to identify the minerals composition, discuss the sedimentary environment and sediment source, and propose a comprehensive prospecting direction for key metal minerals using XRD analysis, TIMA analysis, and detailed geochemical research. The results demonstrate that the T₂/T₃ boundary claystone in the Zhenba area is mainly composed of quartz, illite, and kaolinite, with small amounts of chlorite, montmorillonite, and sudoite. The major elemental characteristics (SiO₂, Al₂O₃, ^TFe₂O₃, TiO₂) indicate that the boundary claystone belongs to bauxite mudstone. The CIA (chemical index of alteration) and ICV (index of compositional variability) values range from 85 to 93 and 0.22 to 0.46, respectively, indicating that the sedimentary parent rock has undergone significant chemical weathering processes. Currently, the claystone found in unconformities in China includes iron-aluminum claystone, aluminum claystone, and bauxite rock. These represent ancient weathering crust sediments, and important metal minerals such as lithium (Li), gallium (Ga), rare earth elements (REE), and niobium (Nb) are produced. The formation age is primarily Carboniferous-Permian, exhibiting characteristics of multi-element comprehensive mineralization. This paper suggests that comprehensive exploration of claystone on unconformity surfaces should be strengthened in the future to facilitate new breakthroughs in prospecting.