断陷湖盆斜坡带重力流砂体沉积特征及沉积模式——以沾化凹陷渤南洼陷南部斜坡带沙三段为例

Characteristics and model of gravity flow sand body deposition in the slope zone of rifted lacustrine basin:A case study from the Sha3 member in the south slope zone of Bonan Sag,Zhanhua Depression

以沾化凹陷渤南洼陷南部斜坡带沙三段为研究对象,综合中外重力流沉积理论的最新研究成果,根据岩心、粒度和测井等资料,对研究区重力流砂体的沉积特征、形成机制和沉积模式进行研究。结果表明:依据流变学特征和沉积物支撑机制可以将渤南洼陷南部斜坡带重力流砂体划分为滑动-滑塌砂体、砂质碎屑流砂体和浊流砂体3种类型。其中滑动-滑塌砂体呈孤立状发育,具有丰富的同沉积变形构造;砂质碎屑流砂体呈厚层块状,内部常发育漂浮的泥砾;浊流砂体以薄层砂、泥岩互层为主,具有正粒序。研究区斜坡带上部以滑动-滑塌砂体为主,中、下部发育以砂质碎屑流砂体为主的沟道微相和以浊流砂体为主的沟道侧缘微相,整体呈条带状展布;洼陷带发育以砂质碎屑流砂体为主的沟道末端微相和以浊流砂体为主的沟道间及席状砂微相,整体呈扇状展布。依据研究区重力流砂体的分布规律及形成机制,建立多物源、富泥贫砂条件下的断陷湖盆斜坡带重力流砂体沉积模式。

Combined with the latest research progress of gravity flow deposition theory at home and abroad,the sedimentary characteristics,formation mechanism and sedimentary models of the gravity flow sand bodies in the Sha3 member of the slope zone in the southern part of the Bonan Sag in Zhanhua Depression were studied systematically using core data,granular analysis,well logging and other information. The research shows that the gravity flow sand bodies mainly include sliding-slump sand bodies,sandy debris flow sand bodies and turbidite sand bodies based on the rheological characteristics and sediment support mechanism in the study area. The sliding-slump sand bodies distribute dispersedly with abundant synsedimentary deformation structures;the sandy debris flow sand bodies are thick and massive with floating mud gravel inside;the turbidite sand bodies area mainly composed of thin layer sand and mudstone with the coarsening upward succession. The sliding-slumping sand bodies are mainly distributed at the upper part of the slope zone;the channel microfacies dominated by sandy debris flow sand bodies and the channel edge microfacies dominated by turbidite sand bodies develop at the middle and lower part of the slope zone,which presents a belt-like distribution. The channel end microfacies dominated by sandy debris flow sand bodies and the interchannel and the sheet sands microfacies dominated by turbidity sandbodies distribute in the sag zone,which presents a fan-like distribution. According to the distribution law and formation mechanism of gravity flow sand bodies in the study area,the sedimentary model of gravity flow sand bodies in the slope zone of rifted lacustrine basin was established under a multi-source,mud-rich and sand-less condition.