深水环境下古水流方向分析和阻塞浊流沉积的识别——以鄂尔多斯盆地桌子山地区上奥陶统拉什仲组为例  

Analysis of paleocurrent direction and identification of ponded turbidity current deposits in deep water environment:a case study of the Upper Ordovician Lashenzhong Formation in Zhuozishan area,Ordos Basin

作　　者：李向东[1] 陈海燕 Li Xiangdong;Chen Haiyan(School of Land Resource Engineering,Kunming University of Science and Technology,Yunnan Kunming 650093,China)

机构地区：[1]昆明理工大学国土资源工程学院,云南昆明650093

出　　处：《石油学报》2020年第11期1348-1365,共18页Acta Petrolei Sinica

基　　金：国家自然科学基金项目(No.41272119)资助。

摘　　要：鄂尔多斯盆地西缘北部桌子山地区上奥陶统拉什仲组中发育深水浊流沉积,对其展开沉积学研究具有重要的油气地质意义。在详细的野外观察基础上,结合岩性特征与沉积构造(特别是包卷层理),对拉什仲组浊流沉积中指向性沉积构造(大槽模和小型交错层理)进行了详细的古水流分析。结果表明:大槽模的古水流方向主要为SW向,平均方位为230°,可代表沉积时的区域斜坡方向;小型交错层理具有复杂的古水流样式,依据主、次优势古水流方向与区域斜坡方向的关系,可将古水流划分为顺坡流(浊流)、偏转叠加流、斜反射流和正反射流等区域。综合岩性特征、包卷层理的成因和复杂的古水流样式,可判断桌子山地区拉什仲组具有阻塞浊流的沉积特征。阻塞浊流沉积的发现对于更好地指导鄂尔多斯盆地西缘深水油气勘探具有重要意义。Deep-water turbidity deposits developed in the Upper Ordovician Lashenzhong Formation of Zhuozishan area,northern part of western margin of Ordos Basin,and its sedimentological study is of great significance in oil and gas geology.Based on detailed field observations,in combination with lithological characteristics and sedimentary structures(especially convolute lamination),this study performs the fine paleocurrent analysis of directional sedimentary structures(large flute cast and small cross lamination)in the turbidity current deposits of Lashenzhong Formation.The results show that the paleocurrent of large flute cast flows mainly to the southwest,with the average azimuth of 230°,which can represent the direction of regional slope during deposition;the small cross lamination has complex paleocurrent patterns.Based on the relationships between principal and secondary dominant paleocurrent directions and the direction of regional slope,the paleocurrent can be divided into downslope current(turbidity current),deflecting superposition current,oblique reflection current,and normal reflection current.Comprehensively based on the lithological characteristics,the geneses of convolute laminations and the complex paleocurrent patterns,it can be judged that Lashenzhong Formation in Zhuozishan area presents the sedimentary characteristics of ponded turbidity.The discovery of ponded turbidity current deposits is of great significance to better guide deep-water oil and gas exploration in the western margin of Ordos Basin.

关 键 词：阻塞浊流 古水流 沉积构造 上奥陶统 鄂尔多斯盆地 

分 类 号：TE121.3[石油与天然气工程—油气勘探]