柴达木盆地西部地区新生代盆地性质

The Nature of the Cenozoic Western Qaidam Basin

含油气盆地不同阶段的性质对于恢复盆地的演化过程、评价油气资源生储运条件具有重要意义。本文在总结前人关于新生代柴达木盆地西部地区性质与演化研究的基础上,重新解译现有地震剖面,系统地开展了盆地构造几何形态、沉积速率、沉积相、沉积旋回、沉积中心迁移以及盆地内不整合的接触关系等方面研究。研究表明:作为陆内挤压背景下的巨大坳陷,新生代的柴达木盆地西部地区具有几何剖面形态不对称、沉积速率较高但又低于西部典型前陆盆地、过补偿状态下强烈缩短致使沉积中心迁移、沉积-构造反旋回性质明显发育等特点。柴达木盆地西部地区以狮子沟组为界线,前期发育细粒远源沉积,属压陷盆地;后期沉积速率显著增加,粗颗粒沉积发育,具有非典型的类前陆盆地性质,并由周缘山体构造活动及盆地过补偿状态共同控制。

The characteristics of different stages of petroliferous basins are of great significance for the restoration of basin evolution and the evaluation of hydrocarbon generation,storage and transportation conditions.In this study,we systematically reviewed previous studies on the nature and evolution of the Cenozoic western Qaidam basin.Based on the interpretation of seismic profiles combining with the basin tectonic geometry,sedimentation rate,sedimentation phase,sedimentation cycle,sedimentation center migration and unconformity contact relationship within the basin,we concluded that the Cenozoic western Qaidam basin,as a large intracontinental depression in a compressional environment,has an asymmetric geometric configuration in the seismic section,high deposition rate but slightly lower than the western typical foreland basin,and migration of sediment centers due to strong shortening under overcompensation,with obvious reverse cycling sedimentary-tectonic development.Importantly,the deposition of Shizigou Formation is considered as the sedimentary boundary of the Cenozoic western Qaidam basin,showing that in the early stage,fine-grained far-source sediments were developed,belonging to a depression basin;While,in the later period,the sedimentation rate increased significantly,and the coarse-grained deposition developed,which had the characteristics of atypical foreland basin.The fact significantly suggests that it’s controlled by the combination of tectonic activity of the surrounding mountains and overcompensation state of the basin.