四川盆地井研地区麦地坪组-筇竹寺组高分辨率层序地层特征

Characteristics of high-resolution stratigraphic sequence of Maidiping Formation and Qiongzhusi Formation in Jingyan area,Sichuan,China

为了更准确地研究四川盆地井研地区下寒武统麦地坪组-筇竹寺组沉积的变化规律,将岩石学、常规测井分析方法与元素测井单元素、元素比值综合分析相结合,精细划分和研究其高分辨率层序地层特征。将麦地坪组-筇竹寺组划分出3个中期旋回(MSC)、20个短期旋回(SSC)。受构造运动影响,MSC2上升半旋回沉积时期,各井各短期旋回发育情况有所差异,JS1井和JY1井缺失SSC6~SSC9,JY2井缺失SSC6~SSC8。以此建立等时地层格架,分析发现MSC1沉积时期各井各短期旋回均正常发育,此时各井沉积古地理位置相当;MSC2上升半旋回时期井研地区底部SSC6~SSC9不同程度缺失,说明此时该区域沉积部位相对较高,位于拉张槽西侧斜坡带,且JS1井和JY1井高于JY2井,其沉积古地理明显呈阶梯状。以此建立沉积模式发现,研究区MSC1时期主要继承埃迪卡拉纪岩溶谷地古地貌,发育与ZY1井相似沉积;MSC2时期受兴凯地裂运动形成的拉张槽影响,研究区位于拉张槽西侧宽缓斜坡带中部,古地理位置较ZY1井略高,研究区内呈西高东低的阶梯状古地理格局,两个沉积时期沉积中心发生了部分偏移;在此填平补齐沉积阶段后,研究区在MSC3沉积时期进入正常宽缓的西浅东深的陆棚相沉积体系,研究区位于西侧较高部位,主要发育浅水陆棚沉积,海平面短时上升时,发育少量深水陆棚沉积。

Characteristics of high resolution stratigraphic sequence of lower Cambrian Maidiping Formation and Qiongzhusi Formation in Jingyan area of Sichuan Basin are meticulously divided and studied by analysis method of petrology and conventional logging and the comprehensive analysis of element and element ratio in elemental logging. The Maidiping Formation and Qiongzhusi Formation in the study area can be divided into 3 medium term cycles （MSC1-MSC3） and 20 short term cycles （SSC1-SSC20）. As for the medium term cycles, the MSC1 can be subdivided into 5 short-term cycles of SSC1-SSCS, the MSC2 can be subdivided into 8 short term cycles of SSC6-SSC13, and the MSC3 7 can be subdivided into 8 short-term cycles of SSC14-SSC20. Affected by tectonic movement, the development of short term cycles in different drilling wells in the study area is different during the period of MSC2 ascending hemicyclic sedimentation. SSC6-SSC9 short term cycles are absent in Well JS1 and Well JY1, and SSC6-SSC8 is absent in Well JY2. The established isochronous stratigraphic framework shows that the short-term cycles of all the drilling wells in the MSC1 sedimentary period are normally developed, and the location of sedimentary palaeogeography of each well is almost the same. There are different degrees of absence of SSC6-SSC9 in the Jingyan area in MSC2 medium term, indicating that the depostional area in this region is relatively high, and located in the west slope of the stretching trou JY2, displaying a ladder the dev gh. Moreover, the location of Well JS1 and Well JY1 are higher than We shaped sedimentary palaeogeomorphology. The established sedimentar elopment of MSC1 in the study area is similar to that of Well ZY1 an inherited the palaeogeomorphology of karst valley is located in the wide gentle slope belt, west taphro ladder genesis, and the location of palaeogeography paleogeographic pattern, with the west higher than the east. Partial shift of the sedimentary center occurred during the two sedimentary periods. A{ter this sedimentary stage of filling and leveling up, the sedimentary system of shelf sedimentary facies appears, characteristic of shallow relief in the west and deep relief in the east in MSC3 depositional stage, and the study area is located in the higher place of the west side, developed shallow water shelf deposits, with minor deep shelf deposition when short term sea level rises.