湖盆扇三角洲河口坝发育程度及粒度韵律特征:以滦平盆地桑园剖面下白垩统西瓜园组为例  

Sedimentary characteristics of mouth bar within lacustrine fan delta: insights from the Lower Cretaceous Xiguayuan Formation of Sangyuan outcrop, Luanping Basin

作　　者：张可[1] 吴胜和[1] 许允杰 熊绮聪 高子杰 余季陶 Zhang Ke;Wu Sheng-He;Xu Yun-Jie;Xiong Qi-Cong;Gao Zi-Jie;Yu Ji-Tao(College of Geosciences,State Key Laboratory of Petroleum Resources and Prospecting,China University of Petroleum(Beijing),Beijing 102249,China)

机构地区：[1]中国石油大学(北京)地球科学学院,油气资源与探测国家重点实验室,北京102249

出　　处：《古地理学报》2022年第3期415-432,共18页Journal of Palaeogeography：Chinese Edition

基　　金：国家自然科学基金项目(编号:42002112)资助。

摘　　要：扇三角洲作为重要的油气储集场所,其成因单元类型及分布特征控制着油气的差异分布及采出效率。关于扇三角洲分流河道沉积特征已有共识,但河口坝沉积特征尤其是韵律特征尚存在争议。以滦平盆地桑园剖面下白垩统西瓜园组湖盆扇三角洲沉积体为例,通过人工实测及无人机观测相结合的方法,对河口坝沉积特征、尤其是韵律特征进行研究,利用水槽模拟实验阐明河口坝韵律特征的形成机理。结果表明,河口坝在整个剖面中占砂(砾)岩体的45.27%,分流河道和席状砂分别占53.42%和1.31%。河口坝在剖面上呈底平顶凸状,通常由多期增生体组成。当增生体主要由砂岩组成时,呈粒度反韵律特征;而当增生体主要由砾岩组成时,呈粒度正韵律特征。河口坝整体韵律受控于增生体的垂向叠置样式,既可呈反韵律特征又可呈正韵律特征。当流量、沉积底形坡度等地质条件一定时,河口坝内部增生体韵律性主要受沉积物粒度控制。当沉积物粒度较细时,河口水流扩散模式为底床摩擦力主控,增生体呈现反韵律特征;而当沉积物粒度较粗时,河口水流扩散模式为惯性力主控,河口坝增生体则呈现正韵律特征。Fan delta is an important hydrocarbon reservoir and its genetic unit type and distribution strongly influence the hydrocarbon distribution and recovery efficiency. Although there is a consensus on the sedimentary characteristics of distributary channels, the sedimentary characteristics of mouth bar, especially the vertical grain-size trend, are still controversial. Field survey and unmanned aerial vehicle(UAV)observation were used to investigate the lacustrine fan delta of the Xiguayuan Formation of Lower Cretaceous in Sangyuan outcrop, Luanping Basin, and flume simulation experiment was done aiming to analyze the sedimentary characteristics of mouth bar and reveal the formation mechanism of vertical grain-size trend. The mouth bars account for 45.27% of glute nite bodies, while the distributary channels and sheet sand account for 53.42% and 1.31% of glutenite bodies, respectively. The mouth bar with a flat bottom and convex top mainly consists of sandy and gravelly accretions. The sandy accretion shows an overall coarsening upward trend, and gravelly accretion shows the fining upward trend. The vertical grain-size trend of mouth bar is controlled by superposition patterns of the accretion bodies, which shows either coarsening upward trend or fining upward trend. Under constant discharge and slope of depositional bedform conditions, finer sediment induces a coarsening upward trend of accretion within the mouth bar dominated by the friction-dominated effluent, while the accretion with coarser sediment results in the coarsening upward accretion controlled by the inertia-dominated effluent diffusion.

关 键 词：扇三角洲 河口坝增生体 韵律特征 西瓜园组 下白垩统 桑园剖面 滦平盆地 

分 类 号：P588.2[天文地球—岩石学]