渤中西环古近系东营组物源转换与沉积充填响应

通过砂岩中碎屑锆石U-Pb年龄分析、火山碎屑组分含量变化、地震多属性分析、层序地层格架与沉积充填特征综合分析,认为东二段沉积时期渤中西环的物源供给方式、层序地层格架及沉积充填特征发生明显的变化.东二下段沉积期前,湖盆处于强烈裂陷期,中-深湖相泥岩发育,物源主要为盆地内部的中生代火成岩基底,沉积层序明显受盆内低凸起控制,在盆内低凸起四周发育一系列近源的扇三角洲朵体;东二下段沉积期后,湖盆处于断-坳过渡期,盆内低凸起四周的断裂活动减弱,沉积层序逐渐向盆内低凸起超覆,盆外太古代-元古代变质岩物源供给不断加强,近源的扇三角洲砂体逐渐向远源的辫状河三角洲砂体转化,同时发育宽广的滨浅湖环境.渤中西环古近纪沉积充填过程中,地层样式、沉积模式与物源供给方式的一致性变化,体现了裂陷湖盆充填演化的内在规律,为我国东部裂陷盆地演化及裂陷旋回划分提供了新的线索.

The Provenance Transformation and Sedimentary Filling Response of Paleogene Dongying Formation in Western Slope of Bozhong Sag

Through comprehensive analysis of U-Pb age analysis of detrital zircons in sandstones, change of the content of tephra component, seismic multi-attributes analysis, sequence stratigraphic framework and sedimentary filling, considering that in the Donger member sedimentary period, the provenance supply mode, the sequence stratigraphic framework and sedimentary filling characteristics of the west of Bozhong sag changed obviously. In the sedimentation of SQd_2L and it's earlier stage, lake basin was in the intense rift stage, structure activities were intense, basin was interphase concave-convex, sedimentation rate of the basin was accelerated, depth of water deepened, stratum deposited thickly as a whole, lithology were mainly gray-dark grey mudstones conainning lamina medium-fine sandstones and siltstones, granularity was fine as a whole, provenance was mainly the local provenance like Shijiutuo uplift and Shaleitian uplift and Mesozoic igneous rock basement inside the basin, et al, content of tephra in sandstones was high, Mesozoic zircons were also rich, seismic multi-attributes ichnography show that sandstones in the Shijiutuo uplift and Shaleitian uplift two sides were rich, area of red zone is large, sedimentary sequence was obviously controlled by the lower uplifts inside the basin and faults around them, sequence characteristics have remarkable differences between the direction parallel and perpendicular to the provenance, in the direction parallel to the provenance, sequence at Shaleitian side was ansymmetrical cycle which took declining half cycle as principal, it's GR electrical characteristics were smooth finger, the braided river delta sand bodies which distributed approximately to EW were developed, however, sequence at Shijiutuo uplift side took LST which was rising half cycle as principal, it's GR electrical characteristics were infundibulate and box combination, multi-phase fan delta lobes were developed, in the seismic section passing the fan along the provenance direction at the two uplifts, typical foreset features were visible. In the direction perpendicular to the provenance, however, there mainly no significant difference, sequence was ansymmetrical cycle which took declining half cycle mainly, it's GR electrical characteristics were medium-high amplitude finger, shore shallow lake-braided river delta facies were developed; After the sedimentation of SQd_2L, lake basin was in the fault depression-depression transition period, area of lake basin was large, depth of water was shallow, fault activities around the lower uplifts inside the basin weakened obviously, stratum was thin as a whole, lithology were primarily conglomeratic sandstones, medium-fine sandstones and siltstones, monolithic granularity was fine, clastics inside basin were mainly came from Yanshan tectonic belt (regional provenance) in the northwest part of the sag, content of tephra in sandstones reduced visibly, detrital zircons in sandstones were primarily Proterozoic zircons, seismic multi-attributes ichnography show that distribution area of red zone decreased obviously, depositional sequence overlapped toward low uplifts inside basin, sequence characeristics have little differences between the direction parallel and perpendicular to the provenance, sequence was primarily ansymmetrical cycle which took declining half cycle chiefly, it's GR electrical characteristics were low amplitude finger and dentation, proximal fan delta sand bodies transformed gradually to distal braided river delta sand bodies, at the same time, broad shore shallow lake environment was developed. In Paleogene sedimentary filling process of the western slope of Bozhong sag, the consistent changes of the stratigraphic pattern, sedimentary mode and provenance supply mode reflect the inherent law of filling evolution of the rifted basin, provide new clues for evolution and division of rift-subsidence cycles of the rifted basins in the eastern part of our country.