沾化凹陷孤岛西部斜坡带沙三段重力流沉积特征与源--汇体系

Depositional Characteristics and Source to Sink Systems of Gravity Flow of the Third Member of Shahejie Formation in Gudao West Slope Zone of Zhanhua Sag,Bohai Bay Basin,China

以岩芯观察、粒度分析、薄片鉴定、测井资料和地震资料解释等为主要手段,研究渤海湾盆地沾化凹陷孤岛西部斜坡带沙三段主要沉积物重力流类型及其沉积特征,探讨不同触发机制下的沉积物重力流演化过程和构造活动对重力流沉积过程及砂体展布的控制,总结源—汇耦合体系,建立斜坡带重力流砂体发育模式。结果表明:研究区沙三段沉积时期发育异重流、碎屑流、浊流、液化流和滑动—滑塌五种沉积物重力流,具有洪水型和滑塌型两种触发机制,流体演变总体处于碎屑流向浊流演化的早期阶段,推测研究区以北深水区仍发育碎屑流沉积且开始广泛发育浊流沉积。构造作用对研究区沙三段流体性质与演化、同生变形构造和重力流成因砂体的发育与分布具有明显的控制作用。总体上,研究区具有断槽沟谷、断裂坡折、断裂走向斜坡及缓坡沟谷等4种主要的源—汇耦合体系。纵向上,研究区沙三段自下而上由(半)深湖、近岸水下扇、滑塌扇沉积演变为滨浅湖、辫状河三角洲以及扇三角洲沉积;平面上,研究区东部主要发育来自孤岛凸起的扇三角洲前缘和近岸水下扇,西部主要发育来自陈家庄凸起的辫状河三角洲前缘,中部主要发育串珠状滑塌扇体。

By employing the main techniques of core observation, grain size analysis, thin section examination, logdata and seismic data interpretation etc., the major types and sedimentary characteristics of sediment gravity flows inthe third member of Shahejie Formation in Gudao west slope zone of Zhanhua sag in the Bobai Bay Basin were studiedin this paper. Their control factors under different triggering mechanisms and tectonic activities over the sedimentaryprocess of gravity flows and sand body distribution were discussed, the source-to-sink coupled systems were summa-rized and the development mode of gravity flow sand bodies in the slope zone were established. The results indicatedthat five types of sediment gravity flow, including hyperpycnal flows, debris flows, turbidity currents, fluidized flows,and slides-slumps were developed during the sedimentary period of the third member of Shahejie Formation in thestudy area, and involving two triggering mechanisms, namely, flood and slump. The fluid evolution was in general atthe early stage of evolution from debris flow to turbidity current, and it is predicted that in the deep waters to the northof the study area, debris flow sediments were still developed and turbidity current sediments started to develop exten-sively. Tectonic action exerts significant control over fluid property and evolution, development and distribution of con-temporaneous deformed structures and sand bodies of gravity flow origin in the third member of Shahejie formation inthe study area. In general, there are four major source-to-sink systems occurred, including fault trough gully, faultslope break, fault strike slope, and gentle slope gully, respectively. Vertically, the （semi） deep lake, nearshore sub-aqueous fan and slump fan deposition were evolved into shore-shallow lake, braided delta and fan delta depositionfrom the bottom up in the third member of Shahejie Formation. On the plane, fan delta front and nearshore subaqueousfan from Gudao uplift are mainly developed in the east part of the study area whereas braided delta fronts are mainlydeveloped in the west part of the study area, and slump fans in bead string pattern are mainly developed in the middlepart of the study area.