渤海湾盆地沙南凹陷构造发育与演化特征

沙南凹陷一直是渤海海域油气勘探的难点和热点，盆内油气分布表现出极强的不均衡性，复杂的构造特征成为制约油气差异成藏的关键。为探讨沙南凹陷构造演化特征，本文首次利用新三维地震及钻井资料，对地层展布特点、断裂体系特征进行精细刻画，新识别出中生代逆冲构造体系，并结合区域地球动力学背景，对新生界沉积-沉降中心迁移规律及全区构造发育演化特征等方面进行了详细分析。研究表明，沙南凹陷盆地结构表现为“三段式”，中、新生代断裂体系主要发育3期，即中生代逆冲断裂系、古近纪伸展断裂系和新近纪晚期共轭走滑断裂系，控制了盆地4个主要构造变革期，分别为早剥晚沉(中生代)、初始强裂陷(沙河街组沉积时期)、二次强裂陷-断坳过渡(东营组沉积时期)以及热沉降-共轭走滑阶段(新近纪)。沙南凹陷的2个沉积-沉降中心——东、西两洼的演化过程(尤其是东营组沉积时期)具有较大差异，控制了两洼烃源岩生烃规模和成熟度的差异，对油气的区域分布起到关键控制作用。地幔热隆起和板块的重组是控制断陷盆地演化的深层动力因素。该研究可为沙南凹陷进一步的油气勘探提供一定借鉴和指导。

STRUCTURAL CHARACTERISTICS AND EVOLUTION OF THE SHANAN SAG OF BOHAI GULF BASIN

The Shanan Sag is a difficult and hot spot in oil and gas exploration of the Bohai Sea area, and the distribution of oil and gas in the basin is extremely unbalanced. Complex tectonics is supposed to be the key factors restricting hydrocarbon accumulation. In order to research the tectonic evolution characteristics of the Shanan Sag, this paper meticulously depicted the stratigraphic characteristics and faults distribution of the sag, based on the newly acquired 3D seismic data and drilling data. Newly identified are the Mesozoic thrusts and the evolution of the tectonic characteristics in the Mesozoic-Cenozoic as well as the Cenozoic subsidence and sedimentation center of the Shanan Sag. The results show that the Shanan Sag consists of three parts from west to east, i.e. the western sag, the central ridge and the eastern sag. The faults in the study area are predominantly in NW trending, subparallel in EW and NE trending. There are three stages of fault systems developed in the Mesozoic and Cenozoic, which are the thrust fault system in Paleozoic, the extensional fracture system in Paleogene and the conjugate slip fault series in late Neogene. On the control of these faults, four stages of tectonic evolution can be recognized from Mesozoic to Cenozoic, including the Mesozoic denudation-subsidence stage, the initial strong chasmic stage (E2s3-E3s1), the transitional period from the second strong chasmic to depression (Ed3-Ed1), and the thermal subsidence and conjugate strike-slip period (Neogene). The change of the Paleogene stress field suggests that the bottom of the Dongying Formation is the essential tectonic boundary. The evolution of the two subsidence and sedimentation centers of the Shanan Sag (the eastern sag and the western sag respectively) is very different, especially in the depositional period of Dongying Formation, which controls the scale and maturity of the source rocks in the two centers mentioned above. Basin structures and tectonic evolution, as well as the regional dynamics background demonstrate that the mantle upwelling may be the direct cause for the basin rifting. The configuration of the periphery plates controlled the evolution of the faulted basin and the directions of fault systems. This study can provide some reference and guidance for further oil and gas exploration in the Shanan Sag.