Abstract: The Lower Qiulitag Formation of the Upper Cambrian in Tabei area is adjacent to the Northern Depression and the Kuche Depression, with dual hydrocarbon supply conditions and favorable petroleum geological conditions. The breakthrough in the Xiongtan 1 well had revealed its significant exploration potential. The researches of the detailed sedimentary characteristics, micro-facies distribution patterns, and sedimentary models within a sequence framework were lack in the Lower Qiulitage Formation, which restrict the further exploration of the Lower Qiulitage Formation. Through the measurement of 2334.4 meters of strata in six sections in the Xiaoerblak outcrop area, as well as the measurement of GR curves and carbon isotope curves in two sections, 555 samples collection and making thin sections for analysis, the stratigraphic and sequence characteristics, sedimentary features, and depositional models of the Lower Qiulitag Formation were systematically identified. Based on the comparison of lithology, GR curves and carbon isotope curves, it has been clarified that the Lower Qiulitage Formation in the study area corresponds to SQ7 and the top-missing SQ8 in the platform-basin region. The main rock types include granular dolomite, thrombolite dolomite, stromatolite dolomiteand laminated dolomite. The overall depositional environment was a restricted platform facies, comprising 5 subfacies and 6 microfacies，which grouped into 7 typical sedimentary sequences. Influenced by the Wensu-Yaha paleo-uplift, during the SQ7 period, the deposition was characterized by tidal flat subface with frequent cyclic changes of various microfacies, showing minor lateral variations. And a depositional model was established, that the supratidal zone, intertidal zone, and subtidal zone developed sequentially from the paleo-uplift toward the basin. During the SQ8 period, the deposition transitioned from tidal flat subface to intra-platform shoal subface, with significant lateral differences in the proportions of mound and shoal，And a depositional model was established, that the intertidal zone, subtidal high-energy zone, and intra-platform shoal developed sequentially from the paleo-uplift toward the basin. There wewe 61~74 sedimentary sequences developed inside the outcrop area of SQ7, and a single sedimentary sequence can form a high-quality reservoer-cap combination. The sedimentary sequences developed continuously in the over-100-meter stratum have the potential to form an overlapping and contiguous lithologic reservoir.The reservoir is widely developed in SQ8 and has the potential to form high-quality structural oil and gas reservoirs. The west Tabei area, controlled by Wenshu-Yahagu uplift, widely developped mound and shoal reservoirs with high quality. When somewhere was overlaid by tight lithology and existing fractures of connected source rock, high-quality oil and gas reservoirs were easy to form, which is a favorable area for exploration.The research results provide the direction for the next oil and gas exploration of Lower Qiulitag Formation in Tabei area.

Key words: Tabei Area, Lower Qiulitage Formation, marine carbonate rock, dolomite, sedimentary characteristics, depositional model