南堡凹陷高北地区“异迁移”型层序构型成因及其对沉积的意义

Genetic Mechanism of Allogenic Migrated Sequence Stratigraphic Architecture in Gaobei Area of Nanpu Sag and Its Significance for Sedimentation

受到区域性幕式构造活动的影响,南堡凹陷高北地区沙河街组时期发育典型的"异迁移"型层序地层构型.充分利用钻井、测井和高分辨率三维地震等资料,运用层序地层学和沉积盆地分析相关理论和方法,系统地研究了"异迁移"型层序构型的特征和成因机制.结果表明,南堡凹陷高北地区沙河组为3个二级层序、7个三级层序(SQ1~SQ7),在地震剖面上呈现出独特的"跷跷板式"交替增厚的横向叠加特征.其中,SQ1~SQ2层序主要发育于盆地西侧,SQ3~SQ4层序在盆地两侧均匀发育,SQ5~SQ7层序主要发育于盆地东侧.多重因素相互叠加形成了这种独特的层序构型:(1)幕式运动造成边界断层活动性发生东西转换,从而导致层序沉积中心自西向东大范围迁移;(2)不同时期板块活动引起区域应力场的方向发生顺时针旋转,使得控凹断层由早期的NW-SE向逐渐变为N-S向;(3)不同类型的断层组合样式也影响着沉积中心发育的位置和规模,从而导致了研究区沙河街组时期层序发生大范围的迁移."异迁移"型层序在侧向迁移过程中,不同层序内发育的沉积相特征和充填样式均发生自西向东规律性的转移,提出"异迁移"型层序构型成因机制的研究可以更好地为幕式构造活动背景下陆相断陷湖盆沉积层序演化提供新的思路和见解.

Due to the effect of regional episodic tectonic activity,typical allogenic migrated sequence stratigraphic architecture is developed in the Shahejie Formation in Gaobei area of Nanpu sag.Based on the drilling,logging and high-resolution 3 D seismic data,the characteristics and genetic mechanism of allogenic migrated sequence stratigraphic architecture are systematically studied,using structural sedimentology and sequence stratigraphy theories and methods.The results show that Shahejie Formation in the Gaobei area of Nanpu sag can be divided into three second-level sequences,which can be subdivided into seven third-level sequences(from SQ1 to SQ7).The SQ1-SQ7 sequences of Shahejie Formation present a continuous lateral stacking patterns of"see-saw"alternating thickening in the seismic profile.Among them,SQ1-SQ2 sequences are mainly developed in the west side of the basin,SQ3-SQ4 sequences are evenly developed on both sides of the basin,and SQ5-SQ7 sequences are mainly developed in the east side of the basin.Multiple factors result in this unique sequence architecture.(1)Episodic movement causes east-west differences in boundary fault activity,which leads to a large scale migration of sedimentary center from west to east.(2)The direction of the regional stress field caused by plate activities in different periods rotates clockwise,making the subsag controlling fault gradually change from the NW-SE direction in the early stage to the N-S direction.(3)Different types of fault assemblage patterns affect the location and scale of depositional center development,and thus control the migration and evolution of allogenic sequence stratigraphic architecture.In the process of lateral migration,the characteristics of sedimentary facies and filling patterns under the control of sequence stratigraphic units in different transition stages all move from west to east regularly.It is concluded that research on the genetic mechanism of allogenic migrated sequence stratigraphic architecture can provide new insights into the evolution of lacustrine rift basin sedimentary sequence under the background of episodic tectonic activity.