四棵树凹陷超深层裂谷盆地的厘定及油气勘探意义

准噶尔盆地南缘西段四棵树凹陷下部成藏组合获重大勘探突破,凹陷的深部构造、盆地结构和原型盆地备受关注。利用最新二维地震资料,解析凹陷深层地震反射和构造特征,厘定盆地性质,结合平衡剖面方法,恢复了盆地构造演化过程。研究表明,四棵树凹陷石炭系—新生界均有发育,由老至新地层展布范围逐渐扩大,厚度中心整体具有继承性。该凹陷具有裂谷盆地的断拗二元结构,以侏罗系底为界,其下为断陷结构,可见原型盆地的边界断层,沉积厚度大,范围小,发育火山—碎屑岩沉积组合;其上为拗陷结构,断层不发育,沉积厚度小,范围大,发育侏罗纪—白垩纪陆相碎屑沉积。结合区域构造演化史与局部地质结构特征,四棵树凹陷的演化可分为断陷和拗陷2个阶段,断陷阶段可能相对独立,拗陷阶段与准噶尔盆地主体连接为湖盆。高泉断裂属于裂谷盆地边界断裂之一,为同沉积正断层,持续活动,晚期遭受挤压反转。受裂谷盆地控制,断陷期二叠系—三叠系泥页岩和拗陷期侏罗系煤层,是四棵树凹陷超深层的重要烃源岩,油气勘探潜力大。

Discovery of Ultra?Deep Rift Basin and Its Petroleum Exploration Significance in Sikeshu Sag,Junggar Basin

A major breakthrough in petroleum exploration has been made in the Sikeshu sag of the southern margin of Junggar basin and the deep geological structures,basin framework and prototype basin in the sag have attracted much attention.Based on the latest 2D seis?mic data,this paper analyzes the seismic reflection and structural characteristics of the deep strata in the Sikeshu sag,determines the proto?type basin and restores the tectonic evolution process of the Sikeshu sag.The study results show that the Carboniferous-Cenozoic strata are widely developed in the Sikeshu sag and their thickness centers are inherited.The Sikeshu sag has a fault depression-depression structure.Taking the bottom of the Jurassic as the boundary,the structure under the boundary is a fault depression characterized by thick volcanic?clastic deposits with noted boundary faults of the prototype basin,whereas the structure above the boundary is a depression filled with ter?restrial debris deposits of Jurassic-Cretaceous,which is characterized by undeveloped faults,wide distribution range and thin sedimentary thickness.Combined with regional tectonic evolution and local geological structure,the evolution of the Sikeshu sag can be divided into two stages,namely rift and depression.The Sikeshu sag might have a relatively independent tectonic?sedimentary evolution during the rift stage,and was connected with Junggar basin during the depression stage.This paper believes that the syndepositional Gaoquan fault as one of the boundary faults of the rift basin,was an active normal fault and reversed to a thrust fault in the late stage.The Permian-Triassic shales and Jurassic coal seams controlled by the rift basin are the main source rocks of the ultra?deep strata in the Sikeshu sag and have great petroleum exploration potenital.