蒙古国塔木察格盆地塔南凹陷下白垩统构造层序地层学的初步研究

Abstract

基于钻井地质分层、地震反射界面波组特征并结合沉积学的成果，以构造层序地层学为指导，研究并划分了塔南凹陷下白垩统的地层层序。铜钵庙组是初始裂陷期的沉积，岩性上分为两段，对应2个三级层序SQ1和SQ2。南屯组是主裂陷期的记录，对应1个三级层序，可划分出3个四级层序(Sq31、Sq32和Sq33)，进一步划分出7个五级层序。Sq32的顶面是最大湖泛面，标志凹陷范围在此时达到最大，7个次级构造单元在南屯组沉积期形成。大磨拐河组是断坳转换期的沉积，对应1个三级层序SQ4，划分出2个四级层序。伊敏组是坳陷期的记录，对应的三级层序为SQ5。同生断层活动在层序发育中起了重要作用，按规模分为三级，按展布分为两套。铜钵庙组–南屯组沉积期北东走向的正断层活动，其上盘可容空间明显增大；大磨拐河组–伊敏组沉积早期北北东–近南北向的走滑(或张扭)断层活动。剖面上这两套断层以T22界面(南屯组顶面)为分界。 Based on the drilling data, seismic reflecting horizons, together with sedimentological achievements, in the light of the tectonic sequence stratigraphy, the sequences in the Lower Cretaceous of the Tanan Sag are studied and discriminated. The Tongbomiao Formation, as deposits of the initial rifting stage and being divided into two members lithologically, is correlated to two third-order sequences (SQ1 and SQ2). The Nantun Formation, record of the main rifting stage, is correlated to third-order sequence SQ3, in which three forth-order sequences (Sq31, Sq32 and Sq33), and furthermore, seven fifth-order sequences, are identified. The superface of Sq32 represents the largest lacustrine overflow, which marks blossom phase of the basin developing, and the seven suborder tectonic units formed during this period. The Damoguaihe Formation, as deposits of the stage from fault-depressing to down-warping, is correlated to third-order sequence SQ4, in which two forth- order sequences are identified. The Yimin Formation, record of down-warping stage, is correlated to third-order sequence SQ5. The contemporaneous faulting plays an important role in the sequence developing, which can be separated into three grades and two systems. The NE-orientated normal faulting activates during sedimentary period of the Tongbomiao and Nantun Formations, which results in the containing space enlarged on the upper side. The strike-slip (or transtensile) faulting, with NEN-striking or approximate longitude-striking, moves during sedimentary period of the Damoguaihe Formation and lower part of the Yimin Formation. Vertically, the both fault systems are bounded by the T22 seismic reflecting horizon (the top surface of Nantun Formation).