Abstract: In Tabei area adjacent to Northern Depression and Kuqa Depression, the Upper Cambrian Lower Qiulitage Formation is characterized by dual hydrocarbon source supply and favorable geological conditions for hydrocarbon accumulation, showing significant exploration potential indicated by breakthroughs in Well Xiongtan 1. However, there is a lack of study on the fine sedimentary characteristics, microfacies distribution pattern, and deposition mode in the sequence framework, which restricts further exploration of Lower Qiulitage Formation. Through field stratigraphic survey of six sections (2334.4 m) in Xiaoerblak outcrop area, GR and carbon isotope curves measurement of two sections, and thin section observation of 555 core samples, the stratigraphy and sequence characteristics, sedimentary characteristics, and deposition modes of Lower Qiulitage Formation are systematically analyzed. The correlation of lithology, GR curve and carbon isotope curve clarifies that Lower Qiulitage Formation in the study area corresponds to SQ7 and SQ8 (absence of the top) in the platform–basin region. The main rock types include granular dolomite, clotted dolomite, stromatolitic dolomite and laminated dolomite. The restricted platform facies was dominant, which was subdivided into five subfacies and six microfacies, forming seven types of typical sedimentary sequences. Influenced by Wensu-Yaha paleo uplift, SQ7 is composed of tidal flat subfacies sediments with frequent cyclic changes of various microfacies and minor lateral variation, and a deposition mode of supratidal zone–intertidal zone–subtidal zone from paleo uplift to the basin has been established. During the deposition period of SQ8, the sedimentary subfacies transitioned from tidal flat to intra-platform beach subfacies, with significant lateral differences in the proportion of mound and beach bodies, and a deposition mode of intertidal zone–subtidal high-energy zone–intra-platform beach from paleo uplift to the basin has been established. A total of 61–74 sedimentary sequences are observed in SQ7 in the outcrop area, with high-quality reservoir–cap rock combination developed in a single sedimentary sequence, and the successive sedimentary sequences in the over-100-meter strata have the potential to form superimposed and connected lithologic oil and gas reservoirs. SQ8 is characterized by widely developed reservoirs and has the potential to form high-quality structural oil and gas reservoirs. Controlled by Wensu–Yaha paleo uplift, the mound beach facies reservoirs are widely distributed in the western Tabei area, with good physical properties. In areas with overlying tight lithology and faults connecting to source rocks, high-quality oil and gas reservoirs were easy to form, showing a favorable area for exploration. The research results provide orientations for further exploration of Lower Qiulitage Formation in Tabei area.

Key words: Tabei area, Lower Qiulitage Formation, marine carbonate rock, dolomite, sedimentary characteristics, deposition mode