涠西南凹陷流沙港组二段至一段构造特征及其对沉积的控制作用

Structure characteristics of Weixi'nan sag during Liushagang-2 member to Liushagang-1 member depositional period and its control on sedimentary fill

根据断裂体系和盆地构造格局,分析涠西南凹陷流沙港组二段至一段构造特征;结合沉积相带展布,研究研究区构造对沉积充填的控制作用。结果表明:涠西南凹陷流沙港组二段至一段沉积期主要受NE-NEE向1号断裂控制,2号断裂由相对连续的NEE向大型断裂转变为多条小型的近EW向雁列式断裂,同时次级断裂数量明显减少,断裂方向由NE、NE-NEE向转变为近EW向,与太平洋板块俯冲方向由NNW向转变为NWW向、印度—澳大利亚板块与欧亚板块由软碰撞转变为硬碰撞密切相关;构造格局表现为北西断、南东超特征,流沙港组二段沉积期盆地内沉积水体、沉积范围明显较流沙港组一段沉积期的更深、更广,且在凹陷内2号断裂转变形成多个近EW向的构造转换带,成为沉积物有利搬运通道;半深湖亚相沉积范围明显减小,扇体沉积范围明显增加,且2号断裂转变形成的构造转换带对凹陷内湖底扇展布具有明显控制作用。该结果揭示涠西南凹陷流沙港组二段至一段构造—沉积耦合关系,可为研究区油气勘探实践提供参考。

Through comprehensive analyses of fault system and basin structure framework,this paper studied structural characteristics of the Weixi’nan sag during Liushangang-2 member to Liushagang-1member depositional period.And based on the study of sedimentary fill characteristics,this paper tried to unravel the control of structural characteristics on sedimentary fill in Weixi’nan sag.The result shows that during Liushangang-2member to Liushagang-1member depositional period Weixi’nan sag was dominantly controlled by NE-NEE trending boundary fault,named No.1fault,whereas large,relative continuous No.2fault that was NEE trending became en echelon faults arranged by many small,discontinuous EW trending secondary faults.Meanwhile,the number of secondary faults decreased significantly,and fault directions were mainly transferred from NE and NE-NEE trending into EW trending,which was closely related to the transition of subduction direction of Pacific Ocean from NNW trending into NWW trending,the transition of collision between India-Australia plate and Eurasian plate from soft collision to hard collision.During Liushagang-2member to Liushagang-1member depositional period,the structure framework of Weixi’nan sag was NE trending half-graben basin that faulted in the northwest part and overlapped in the southeast part.The sedimentary water depth and areas of Liushagang-2 member depositional period were deeper and wider than Liushagang-1member depositional period,and the transition of No.2fault formed many EW trending structural transfer zones within sag,which was helpful to the sedimentary transportation.The sedimentary characteristics of study area were corresponding to the basin structure characteristics.From Liushagang-2 member to Liushagang-1 member depositional period the areas of semi-deep lacustrine facies sediment decreased obviously,while the areas of fan sediment increased significantly,and structural transfer zones formed by the transition of No.2fault played a great role in controlling the distributions of sub-lacustrine fan within sag.The study results reveals the interaction between structure characteristics and sedimentary fill in Weixi’nan sag during Liushangang-2member to Liushagang-1member depositional period,which provides the oilfield exploration and development with a degree of instructions in study area.