A Study On Sedimentary Sequence Evolution Of The Middle-Lower Ordovician In Shunbei-Shunnan Area In Tarim

Based on the core,thin section,well logging,geochemistry,and seismic data,combined with previous research,the author analyzed the development of sedimentary facies and the division of sequence boundaries in the research area,and introduces a numerical simulation software-Dionisos to study on the deposition process of the Penglaiba Formation to the Yijianfang Formation of the Middle-Lower Ordovician in the Tarim Shuntuo area.The results show that there are five types of sedimentary facies: the restricted platform,open platform,platform margin,platform slope,and slope foot in the Middle-Lower Ordovician of Shunbei-Shunnan area in the Tarim Basin,further subdivided into nine sub-phases: the confined sub-facies,the restricted intra-platform granular beach sub-facies,the open intra-platform granular sub-facies,the open subtropical facies,the intra-tidal tidal flats,the sub-facies subfacies,and the sub-facies Fringe reef subfacies,platform marginal shoal subfacies,and tidal marginal subfacies.Sequence stratigraphic comparison shows that there were five third-order sequences developed in the Middle-Lower Ordovician in Shunbei-Shunnan area,of which the Penglaiba Formation developed two third-order sequences and the Yingshan Formation developed two third-order sequences.Yijianfang Formation developed a third-order sequence.The sedimentary forward modeling results showed that the Middle-Lower Ordovician in the study area experienced a total of five depositional cycles,of which five regional unconformity exposures occurred.A large-scale retreat occurred in Penglaiba in the early stage,which led to the formation of uncovered regional unconformity;and during the Yingshan Formation,there were four local unexploitation exposures along the platform margin;the sea level of the whole area continued to rise during the Yijianfang Formation,and local small-scale unconformity due to structural extrusion.The distribution of the sedimentary facies of the Middle-Lower Ordovician in the study area guides the development and distribution of high-energy facies belts in this area,which lays the foundation for the development of facies-controlled reservoirs;the multi-period short-term exposure is the non-fault controlled surface in this area.