塔北-塔中盆地三叠纪陆相层序地层划分及沉积演化

Continental sequence stratigraphy and sedimentary evolution of the Triassic strata in the North-Central Tarim Basin, Xinjiang

关键词:  塔北-塔中盆地  三叠纪  陆相层序地层  内陆盆地

Key words:  North Central Tarim Basin  Triassic  continental sequence stratigraphy  inland basin

摘要:

塔里木盆地的三叠纪除早三叠世有短暂的海侵外,其余时间均表现为典型的内陆盆地,发育扇-扇三角洲-湖泊沉积体系。三叠纪的塔里木盆地被北部的沙雅隆起剥蚀区和中、西部的塔中剥蚀区分割成南天山前的库车盆地,昆仑山前的塔西南盆地,阿尔金山前的塔东南盆地和中央的塔北-塔中盆地。前三个盆地的三叠系的残留面积不大,其石油地质意义仅表现在生烃方面。而塔北-塔中盆地的三叠系的残留面积大,构成了塔里木盆地三叠系分布的主体,也成为塔里木盆地油气勘探的主要目的层之一。
塔北-塔中盆地的三叠系包含了长周期、中周期和短周期三个级别的基准旋回,其包含有由不整合限定Ⅰ、Ⅱ两个长周期,长周期Ⅰ中可识别一个中周期(Ⅰ₁);长周期Ⅱ中可识别出三个中周期(Ⅱ₁,Ⅱ₂,Ⅱ₃)。塔北-塔中盆地三叠系-侏罗系的有利储集相带与中周期低水位体系域关系密切。盆地中三叠系的3套重要含油气储层Ⅲ油组(T₂a),Ⅱ油组(T₂a)和Ⅰ油组(T₃h),分别对应三个中周期的Ⅱ₁,Ⅱ₂和Ⅱ₃。

Abstract:

Apart from a short period of transgression during the Early Triassic, the Tarim Basin was once a typical nonmarine basin during the rest of the Triassic. In this basin, the fan-fan delta-lacustrine sedimentary systems are well developed. The basin is separated by the Xayar uplift in the north and central Tarim erosional area in the central and western parts into four subbasins:Kuqa Basin at the piedmont zone of the South Tianshan, Southwest Tarim Basin at the piedmont zone of the Kunlun Mountains, Southeast Tarim Basin at the piedmont zone of the Altun Mountains and North-Central Tarim Basin in the central part of Tarim Basin. The emphasis will be placed on the last one in this study because of the widespread occurrence of the Triassic strata as the principal target levels in the North-Central Tarim Basin. These Triassic strata consist of three base-level cycles including long-, medium- and short-period cycles. The long-period cycles Ⅰ and Ⅱ are unconformity-bounded cycles. One medium-period cycle (Ⅰ₁) has been identified in the long-period cycle Ⅰ, while the other three medium-period cycles (Ⅱ₁, Ⅱ₂ and Ⅱ₃) are involved in the long-period cycle Ⅱ. The best reservoir facies zones of the Triassic-Jurassic strata in the North-Central Tarim Basin are closely related to the lowstand systems tract of the medium-period cycles. The Ⅲ oil formation (T₂a), Ⅱ oil formation (T₂a) and Ⅰ oil formation (T₃h) correspond to the medium-period cycles Ⅱ₁, Ⅱ₂ and Ⅱ₃, respectively.