The Xiaochayuan and Bijiashan manganese deposits in the Xiushan area, Chongqing, are located within the Chongqing-Hunan-Guizhou manganese ore belt. They occur in the center of a NE-SW trending secondary graben basin, with ore bodies hosted in black shales of the first member of the Datangpo Formation in the upper Nanhua System, collectively referred to as the "Datangpo-type" manganese deposits. This study investigates the geochemical characteristics and genesis of the Datangpo Formation manganese deposits by focusing on the Xiaochayuan and Bijiashan deposits. Analytical methods includes scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), elemental geochemistry, total organic carbon (TOC) content, and thallium speciation. The results indicate that the Xiaochayuan and Bijiashan deposits share comparable geochemical characteristics. In manganese ores, the concentrations of MnO, CaO, MgO, FeO, and P2O5 are relatively high, while those of Al2O3, K2O, Na2O and TiO2 are relatively low. After Al normalization, trace elements such as Co, Cu, Ga, Mo, Sr, Zn and Ni exhibit varying degrees of enrichment. The manganese deposits display features indicative of hydrothermal sedimentation and are influenced by hydrothermal activities. The scanning electron microscopy images of rhodochrosite ore surfaces reveal a significant positive correlation between the elements Mn and Eu, further indicating that the manganese originates from a hydrothermal system. During the deposition of manganese deposits, the water environment was anoxic, which was conducive to the preservation and evolution of organic matter and the release of large amounts of CO2 through anaerobic oxidation. The concentration of CO32- in seawater reached saturation, leading to direct precipitation of MnCO3 with enriched Mn2+ ions in the sedimentary basin. The discovery provides new evidence for the analysis of the genesis of manganese deposits.