Abstract: In the Sichuan Basin, the Sinian Dengying Formation contains multiple types of dolomite, with micritic dolomite being the dominant type. The origin of micritic dolomite is conducive to the understanding of the dolomitization process and related reservoir evolution of the Dengying Formation. This study investigates the spatial heterogeneity of micritic dolomite, indicating that it is a product of early (syn-depositional and penecontemporaneous) marine diagenesis. In different sedimentary environments, micritic dolomite shows various features: In an environment of restricted platform, micritic dolomite shows lower crystallinity and δ¹³C_carb values, while in an environment of platform margin, dolomite shows higher crystallinity and δ¹³C_carb values, reflecting various dolomitization processes in different settings. In the restricted platform, dolomitization is mainly related to evaporation and early marine diagenetic organic decomposition; in the platform margin and adjacent areas, it may result from microbial sulfate reduction under low-sulfate anoxic conditions. This spatial heterogeneity exerts influence on crystal and related reservoir features.