柴达木盆地的最终定型期——第四纪

Quaternary:the time for Qaidam Basin fell into its final configuration

柴达木盆地发育在结晶基底与褶皱双层基底之上,经侏罗纪的拉张形成断陷、箕状断陷,白垩纪的挤压形成坳陷。早第三纪(古近纪)的拉张同样形成断陷、箕状断陷,晚第三纪(新近纪)—第四纪的挤压也形成坳陷式的沉积盆地。第四纪强挤形成柴达木统一的逆掩逆冲推覆体,在这多层结构的陆盆最终定型形成台南、涩北1号、涩北2号等第四系背斜构造和天然气藏。这些构造在含气部位地震剖面都呈现出"负背斜"异常,这是储层聚集了天然气之后速度变小的正常效应。这一类型天然气藏的发现,使得其他盆地不能忽视第四系油气藏的勘探。

Qaidam Basin was developed on the double basements of both crystal and fold. Fault depression and unsymmetrical fault- depression were formed during Jurassic extension evolution. Fault depression and unsymmetrical fault-depression were also formed during Paleogene extension evolution. Syndeposition type of sedimentary basin was formed during Neogene-Quaternary compressive evolution. The Quaternary strong squeeze caused the formation of unified overthrust and thrust nappes in Qaidam Basin. Finally Quaternary anticlines and gas reservoirs were formed to their final configuration in the continental basin with multiple structural layers, which are called Tainan, Sebei 1 and Sebei 2 and characterized with negative anticline configuration on seismic section due to chimney effect resulted from velocity reducing in the gas-filling-reservoir. The discovery of this type of gas reservoirs indicates that the exploration for gas and oil reservoirs of similar structural style in other basins should not be ignored.