鄂尔多斯盆地东缘保德地区上古生界层序地层与沉积相特征

摘要

为了揭示鄂尔多斯盆地东缘层序地层与沉积相特征,以层序地层学和沉积学理论为指导,对鄂尔多斯盆地东缘保德扒楼沟剖面及周缘上古生界的层序与体系域界面类型、层序结构、沉积相类型及沉积演化进行研究.依据区域性不整合面、下切谷冲刷面、海侵方向转换面和区域性海退面等层序界面将研究区上古生界划分为7个三级层序,分别对应于本溪组、太原组2段、太原组1段、山西组、下石盒子组、上石盒子组和石千峰组.保德扒楼沟及周缘上古生界剖面发育16种岩石类型和8种岩石组合.区内上古生界发育障壁海岸相、碳酸盐岩台地相、辫状河相和曲流河相.SQ1-SQ3中低位体系域发育风化壳和潮道亚相,海侵体系域发育潮坪亚相和潟湖亚相,高位体系域发育碳酸盐岩台地相、潟湖亚相和潮坪亚相;SQ4-SQ7中低位体系域发育辫状河河床亚相,海侵体系域主要发育曲流河泛滥平原亚相,高位体系域主要发育多期曲流河河床亚相—堤岸亚相—泛滥平原亚相的演化序列.区内上古生界经历了由障壁海岸相和碳酸盐岩台地相向河流相的演化过程,沉积演化主要受物源供给、海平面变化和构造活动的控制.%In order to reveal the characteristics of sequence stratigraphy and sedimentary facies of the east margin of Ordos Basin,based on theories of sequence stratigraphy and sedimentology,the sequence and system tract boundary types,sequence structure,sedimentary facies types and sedimentary evolution of the Upper Paleozoic in the Palougou section of Baode area and peripheral sections in eastern margin of Ordos Basin were analysed.According to the several sequence boundaries such as regional unconformity surface,incised valley erosional surface,transgressive direction conversion surface and regional regression surface,the Upper Paleozoic in study area was divided into 7 third-order sequences,corresponding to Benxi Formation,the Second Member of Taiyuan Formation,the First Member of Taiyuan Formation,Shanxi Formation,Xiashihezi Formation,Shangshihezi Formation and Shiqianfeng Formation,respectively.The Palougou and peripheral Upper Paleozoic sections developed 16 rock types and 8 rock association types. The Upper Paleozoic developed barrier coast facies,carbonate platform facies,braided river facies and meandering river facies in the Palougou and peripheral sections.In SQ1-SQ3,the lowstand systems tract developed weathering crust and tidal channel subfacies,the transgressive systems tract developed tidal flat subfacies and lagoon subfacies,the highstand systems tract developed platform facies,lagoon subfacies and flat subfacies.In SQ4-SQ7,the lowstand systems tract developed braided river bed subfacies,the transgressive systems tract developed meandering river floodplain subfacies,the highstand systems tract developed multi-period evolutionary series of meandering river,including river bed subfacies,rive bank subfacies and floodplain subfacies.The sedimentary facies of the Upper Paleozoic in study area shifted from barrier coast facies,carbonate platform facies to fluvial facies,which was mainly affected by provenance supply,sea-level change and tectonic activity.