塔里木盆地塔中-古城地区寒武系沉积体系发育特征与演化

Development Characteristics and Evolution of the Cambrian Sedimentary System in Tazhong and Gucheng Area,Tarim Basin

塔里木盆地寒武系油气勘探在塔中与古城地区相继获得较大发现,但对该地区沉积体系的刻画仍以盆地尺度的岩相古地理编图为依据,缺乏多资料约束下的精细研究。通过岩石学分析对塔中—古城地区寒武系白云岩的原岩进行了细致恢复,其中塔中中下寒武统原岩以泥灰岩、(含膏)粒泥灰岩为主,上寒武统则以粒泥灰岩及颗粒灰岩为主;古城地区原岩多为粒泥灰岩、泥粒灰岩及颗粒灰岩。以地球化学研究为手段,恢复了寒武纪碳酸盐岩沉积期古环境,总体上从早寒武世到晚寒武世,水体深度逐渐增加,盐度降低,蒸发作用减弱。在此基础上,以威尔逊碳酸盐岩综合相模式为指导,划分出了3类沉积相、4类亚相、6类微相。利用三维地震资料的精细解释,刻画了古城地区台缘带礁滩体的发育特征及演化规律,4期礁滩体呈进积式向盆地方向迁移。台缘带礁滩体的迁移演化与台内沉积物的发育特征表明古城台缘带的礁滩体的发育与消亡对塔中台内沉积环境存在较大影响。台缘带的快速生长对台内水体形成围陷,造成了含膏碳酸盐岩的沉积,台内与台缘沉积物形成了良好的对应关系。

The hydrocarbon exploration in Tazhong and Gucheng area in Tarim Basin has made great breakthroughs,but the identification of sedimentary system is still based on the mapping of lithofacies and paleogeography on basin scale,lacking the detailed regional research with the constraints of multiple data.Petrological analysis was used to recover the precursor limestone of the Cambrian in Tazhong and Gucheng area.The lower and middle Cambrian in Tazhong area is dominated by mudstone,wackestone and gypsum-bearing wackestone,while the upper Cambrian mainly developed grainstone and wackestone;and the Cambrian in Gucheng area is dominated by wackestone,packstone and grainstone.The reconstruction of the paleo-environment of the Cambrian in Tazhong and Gucheng area by geochemical analysis shows that the sea water was deepening and the salinity and evaporation was decreasing during the deposition of Cambrian.With the guidance of carbonate comprehensive facies model of Wilson,this area has been divided respectively into 3facies,4subfacies and 6mircrofacies.Based on the interpretation of 3Dseismic data,the development and evolution of the reef-beach bodies of platform margin in Gucheng area was described,showing that the reef-beach bodies of four stages migrated towards the basin in progadation.In stagesⅠandⅡreef-beach bodies developed during the transgression process while in stages Ⅲ and Ⅳ reef-beach bodies developed during the regression process,presenting progradation sedimentary style.The migration characteristics analysis of reef-beach bodies and the development character of inner platform deposits show that the reef-beach bodies of Gucheng platform margin had great influence on the inner platform environment.The quick deposition of carbonate in platform margin resulted in the enclosing of inner platform water and the deposition of gypsum-bearing carbonate rocks.The deposits in inner platform and platform margin have good correspondence.