南襄盆地南阳凹陷地质结构与形成演化

Geologic architecture and tectonic evolution of Nanyang Sag,Nanxiang Basin

南阳凹陷属南襄盆地次级构造单元,是发育在秦岭-大别褶皱造山带之上的富油气断陷。研究其地质结构特征和形成演化过程,对凹陷油气勘探和认识秦岭-大别褶皱造山带晚白垩世以来隆升剥蚀作用的盆地构造-沉积响应均具有重要意义。综合利用凹陷内2/3D地震、钻井、测录井资料,识别区域性不整合面,划分构造-地层层序,刻画主要断裂的构造特征及凹陷平、剖面形态;运用平衡剖面技术,恢复南阳凹陷晚白垩世以来的形成演化过程。结果表明,南阳凹陷发育胡岗组底部(T_(g))、玉皇顶组底部(T_(7))、核桃园组底部(T_(5))、上寺组底部(T_(1))4个区域性不整合面,将凹陷地层划分为基底构造层、胡岗组构造层、玉皇顶组-大仓房组构造层、核桃园组-廖庄组构造层、上寺组-平原组构造层共5套构造-地层层序。受新野断层、禹桐断层、师岗断层等基底断层控制,南阳凹陷表现出南北分带、东西分块、隆凹相间的构造格局。凹陷经历了初始断陷期、持续断陷期、强烈断陷期、断-拗转换期和拗陷期共5期构造演化阶段。基底结构复杂、边界断层形态差异及分段差异沉降是凹陷地质结构的主要控制因素。

Nanyang Depression,a secondary structural unit to the Nanxiang Basin,is a petroliferous fault depression developed in the Qinling-Dabie fold orogenic belt.The study on its geological structure features is of great significance to the hydrocarbon exploration in the depression and the understanding of basional structural-sedimentary responses by the uplifting and denudation of Qinling-Dabie fold orogenic belt.Based on 2D and 3D seismic survey results as well as drilling and log data of the area,this study identified regional unconformities,divided structural-stratigraphic sequences,and characterized the main faults as well as the planar and sectional features of the depression.The evolution process of the depression was also rebuilt with balanced section restoration.The results show that the Nanyang Sag has four regional unconformities at the bottom of Hugang(T_(g)),Yuhuangding(T_(7)),Hetaoyuan(T_(5))and Shangsi Formations(T_(1)),and five recognizable structural-stratigraphic sequences,namely the basement,Hugang Formation,Yuhuangding-Dacangfang Formations,Hetaoyuan-Liaozhuang Formations and Shangsi-Pingyuan Formations.Controlled by several basement faults,i.e.the Xinye Fault,Yutong Fault and Shigang Fault,the Sag is characterized by a tectonic pattern of NS zonation,EW partition and alternate uplift and sag.Five tectonic evolution stages are suggested to have successively shaped the Sag from the initial rift depression to continuous fault depression,strong fault depression,fault-depression transition and final depression.It is therefore concluded that the Nanyang Sag is structurally controlled by its complex basement structure,boundary fault variations and sectional subsidence differentiations.