Abstract: Through outcrop observation, thin section examination and physical property analysis, this paper studied the petrological and reservoir characteristics of the Upper Sinian microbial carbonates on the Shiairike section at the northwestern margin of the Tarim Basin and briefly discussed the origin of the microbial carbonate reservoirs.The microbial carbonates are dominated by microbial dolomites, accounting for 70.37% of the whole Sinian carbonates.Based on having stromatilithic structure or not, the microbial carbonates are divided into stromatolites and non-stromatolites.The stomatolites include stratiform, domal and small isolate columnar types, with the stratiform stromatolites as the main type and pelletoid and micritic lamination as their texture characteristics.In contrast, the non-stromatolites include non-stromatolic cynobactiarial pellet rock and cyanobacterial foam spongy rock, featuring in pelletoid and foam sponge textures.According to physical property, the Sinian microbial carbonate reservoir can be divided into two intervals, with the upper interval being better than the lower.Among the microbial carbonates, the stratiform stromatolites and non-stromatolitic cyanobacterial dolostones especially with foam sponge-like texture are the favorable reservoir rocks.The reservoirs are characterized by fenestal, pellet-associated, foam sponge-associated dissolved porosity as their main reservoir space.The formation and distribution of the microbial carbonate reservoirs are mainly controlled by microfabrics, dolomatization and dissolution.Of these influencing factors, the microfabicsisthe fundamental factor determining the types of the pore space and their texture;the dolomization and dissolution are the critical factors determining the formation of effective pore space.The higher quality of the upper microbial carbonate reservoirs is also attributed to the epigenetic kastification.

Key words: microbial, carboante reservoir, Upper Sinian, Tarim Basin