This paper systematically discusses the multiple source characteristics and formation mechanisms of carbonate-rich fine-grained sedimentary rocks through the analysis of material source and rock formation. The hydrocarbon accumulation characteristics of carbonate-rich fine-grained sedimentary rocks are also summarized. The results show that the main reason for the enrichment of fine-grained carbonate materials in rift lake basins was the supply of multiple material sources, including terrestrial material input, formation of intrabasinal authigenic carbonate, volcanic-hydrothermal material feeding and mixed source. The development of carbonate bedrock in the provenance area controlled the filling scale of carbonate materials in rift lake basins. The volcanic-hydrothermal activity might provide an alkaline fluid to the lake basins to strengthen the material supply for the formation of carbonate crystals. Authigenic carbonate crystals induced by biological processes were the main source of long-term accumulation of fine-grained carbonate materials in the lake basins. Carbonate-rich fine-grained sedimentary rocks with multiple features were formed through the interaction of physical, biochemical and chemical processes during the deposition and post-deposition stages. The source and sedimentary origin of the fine-grained carbonate rock controlled the hydrocarbon accumulation in it. In the multi-source system, the types of “sweet spots” of continental shale oil and gas include endogenous type, terrigenous type, volcanic-hydrothermal type and mixed source type.