局限湖盆滨浅湖滩坝砂体沉积特征——以东营凹陷青南洼陷沙四上亚段为例

滨浅湖滩坝砂体是陆相断陷湖盆最主要的砂体之一,前人对开阔湖盆滨浅湖滩坝砂体的分布规律已有非常深入的研究,但缺少对局限湖盆滨浅湖滩坝砂体分布规律的研究。文中以东营凹陷青南洼陷沙四上亚段为例,利用岩心观察、粒度概率累积曲线等方法,分析了青南洼陷滩坝砂体的沉积特征,剖析了滩坝砂体分布的主控因素,建立了双物源控制下的局限湖盆滨浅湖滩坝砂体沉积模式。研究表明:青南洼陷沙四上亚段沉积时期,滩坝砂体的岩石类型以中砂岩和粉细砂岩为主,成分和结构成熟度中等,沉积构造以反映弱水动力的块状层理和生物扰动构造为主;古物源控制了滩坝砂体的沉积特征,古水动力控制了滩坝砂体的发育规模,由于波浪和沿岸流作用较弱,滩坝砂体的纵向和横向分布距离均较短。

Sedimentary characteristics of shore-shallow lake-beach bar in limited lacustrine basin:taking upper part of fourth Member of Shahejie Formation of Qingnan Sag in Dongying Depression as an example

The shore-shallow lake-beach bar sand is one exploration focus in recent year.Previous studies on the distribution of beach bar sand in wide and slow lacustrine basin have been very thorough,but in restricted lake basins it still needs work.Taking the the upper part of the fourth Member of Shahejie Formation(Es4s)in Qingnan Sag,Dongying Depression as example and using the core observation and analysis of grain size probability curves,the paper demonstrates the sedimentary characteristics and main controlled factors,and sets up a sedimentary model for shore-shallow lake beach bar sand controlled by two types of material sources.The results show that the sand of the lake basin beach bar of Es4s in Qingnan Sag is mainly dominated by medium sandstone and siltstone,and it has medium compositional and structural maturity.The main sedimentary structures are massive bedding and biological disturbance reflecting the weak hydrodynamic conditions.The supplies of material sources and paleohydrodynamic condition control the development characteristics and scales of the beach bar sands respectively.As a result of weaker wave and coastal current action,the longitudinal and transverse distribution distances of beach bar sand are shorter.