鄂尔多斯盆地南部中寒武统张夏组颗粒滩沉积特征及控制因素*
Sedimentary characteristics and controlling factors of grain banks of the Middle Cambrian Zhangxia Formation in southern Ordos Basin

碳酸盐岩颗粒滩是一种十分重要的油气储集体。综合野外露头剖面、岩心、测井、录井及薄片资料,对鄂尔多斯盆地南部地区中寒武统张夏组颗粒滩沉积特征、分布规律及控制因素进行分析。结果表明:研究区张夏组碳酸盐岩颗粒滩沉积广泛发育,以鲕粒滩为典型代表的颗粒滩沉积占绝对优势;颗粒滩岩性主要为颗粒石灰岩、颗粒白云岩和晶粒白云岩3种,颗粒类型主要有鲕粒、生屑、砾屑和砂屑等;颗粒滩纵向上通常表现为下细上粗的反旋回序列,多期旋回垂向叠置,形成相当厚度规模的颗粒滩沉积。结合鄂尔多斯盆地寒武纪岩相古地理特征,认为研究区颗粒滩发育特征及平面展布规律受海平面相对变化、基底古地貌及构造活动综合控制,尤其是鄂尔多斯盆地南部寒武纪近北东向裂陷槽的发育,对张夏组台地边缘带鲕粒滩发育及分布的控制作用更为显著。
The carbonate grain banks serve as important oil and gas reservoirs. In this paper,the sedimentary characteristics,distribution and controlling factors of the grain banks of the Middle Cambrian Zhangxia Formation in southern Ordos Basin were studied by integration of outcrop,core,logging and thin section data. Results show that the carbonate grain banks,dominated by oolitic beach,are extensively developed in the Zhangxia Formation in the study area. The rock types of grain banks commonly encompass grain limestone,grain dolomite and crystalline dolomite,and the grain types primarily consist of oolitic,bioclast,gravel-sized debris and sand-sized debris in the Zhangxia Formation in southern Ordos Basin. The grain banks are characterized by vertically superposed coarsening-upword cycles,which form the grain bank deposition with a considerable thickness. Combined with the Cambrian lithofacies palaeogeographic characteristics in the Ordos Basin,it is considered that the characteristics and planar-distribution of the grain banks are comprehensively controlled by relative sea level change,palaeogeomorphology and tectonic activity. Particularly,the rift trough roughly in NE direction significantly controlled the development and distribution of oolitic beaches in the platform of Zhangxia Formation in southern Ordos Basin