准噶尔盆地二叠纪盆地属性的再认识及其构造意义

New view on the Permian evolution of the Junggar basin and its implications for tectonic evolution

准噶尔盆地及其邻区野外剖面、钻井剖面的系统对比和地震剖面的精细解释表明,二叠系沉积演化、断裂控制沉积、箕状断-超反射特征及大地构造背景均显示,二叠纪准噶尔盆地是形成于张性背景下的断陷-裂陷盆地。准噶尔盆地及邻区火山岩地化特征、年代学数据及区域构造研究成果也证明,二叠纪是张性的大地构造背景。早二叠世—中二叠世早期以发育冲积扇沉积为特征,各构造部位的沉积环境差异较大,强烈断陷并逐渐形成坳隆相间的沉积格局,为断陷盆地的裂陷期;中二叠统中晚期由早二叠世隆坳分割的局面逐渐转化为统一的大型内陆湖盆,吐哈盆地与准噶尔盆地水体相通,形成统一的沉积体系,为断陷盆地扩张期;晚二叠世时期以出现冲积-河流相红色粗碎屑沉积为特征,准噶尔盆地和吐哈盆地分割自成沉积体系,是断陷盆地的萎缩期。因此,中生代盆地演化是建立在二叠纪张性背景的基础之上,二叠纪断陷-裂陷盆地的提出对重新认识中生代盆地演化历程将具有重要启示意义,也将对今后的油气勘探具有重要指导意义,值得进一步研究。

By making full use of field sections, drilling well sections, and seismic sections in the Junggar basin and adjacent areas, northwest China, we have studied the Permian sedimentary evolution, faults, and characteristics of seismic reflection profiles in detail. The Permian sedimentary record, fault-controlled sedimentation, and half graben-structures revealed in the seismic profiles, show that the Junggar basin is a fault-controlled depression that was formed during an extensional tectonic regime in the Permian. This conclusion is confirmed by the recent geochemical and chronologic evidence from volcanic rocks. The first evolutionary stage of the basin spans the period from the Early Permian to the early Middle Permian. This period was characterized by faulting and sediments deposited in alluvial fans. This period also led to the formation of a basin pattern characterized by alternating depressions and uplifts. An extensional stage followed during the middle to late stages of the Middle Permian, which was characterized by widespread sedimentary lacustrine facies. Similar sedimentary successions and geodynamic characteristics in the Turpan-Hami basin suggest that it and the Junggar probably formed as a single basin. The appearance of coarse clastic sediments of alluvial fan-fluvial facies in the Late Permian heralded a compression stage in the evolution of the basins, when different sedimentary successions in the two basins suggest that the Junggar and Turpan-Hami basins became separated. This new view of the Permian Junggar basin is different from previous models of foreland basin accepted by most geologists. Our new model provides further insights into the Mesozoic evolution of the Junggar basin and future petroleum exploration.