The black fine- grained mixed- siliciclastic- calcareous deposits series rich in organic matter are developed extensively in the Yangtze region in early Cambrian. The element geochemical study of the fine- grained mixed deposits series is of great theoretical and practical significance for restoring the provenance in depositional stage, background of source area, palaeoclimate, sedimentary environment and evolution, as well as the reservoir evaluation of the shale and shale gas exploration. Using the newly drilled XYZ- 1 well data in the Lower Yangtze area, based on systematic coring identification of 442. 5 m of Lower Cambrian Mufushan formation, rock thin section, XRD (X- Ray Diffraction), and ICP- MS analysis, the geochemistry of the fine- grained deposits series in Mufushan formation in the early Cambrian is studied in this study. The results show that the lithologic composition of the Mufushan formation is dominated by dark, black calcareous- carbonaceous mudstone, light gray argillaceous limestone, interbeded with dolomitic limestone, cryptite, dolomite, terrigenous carbonaceous limestone, andesite, breccia, etc., mainly composed of siliceous clay- mixed shale facies and siliceous clay- like shale facies, which formed in environment of limited gulf- carbonate platform- tidal systems. During the sedimentary period of the Mufushan formation, there was an alternate paleoclimate of arid- hot and warm- humid, shallow water and relatively deep water paleoceanographic environment indicating normal salinity in general, and showed the vertical direction evolution from oxygen- hypoxia to retained sulfide environment. The provenance of fine grain deposits of the Mufushan formation is derived from the Jiangnan orogenic belt and the Nanjing platform. The sediments in the source area have not undergone sedimentary recirculation and were formed in the tectonic setting of the continental island arc and active continental margin. The offshore confined bay with relatively high sea level, semi- enclosed and reductive environment, and richer TOC content and higher ancient productivity are favorable conditions for the formation of black fine grain mixed sedimentary rock series rich in organic matter.