陆相前陆盆地层序结构特征研究-以准噶尔南缘晚期前陆盆地为例

Research on sequence architectures of continental foreland basins——a case study of the late stage of the southern Junggar foreland basin

陆相前陆盆地层序地层学是目前层序地层学的一个重要研究领域和方向。准噶尔南缘为一两期叠加的复合再生型前陆盆地,综合地震、测井、钻井、露头资料对晚期前陆层序进行了划分,共划分出1个一级层序,3个二级层序,5个三级层序以及15个四级层序。依据前陆盆地构造-沉积演化的旋回性及层序的内部发育特征,将各个二级层序划分出4个体系域。建立了准南前陆盆地层序地层模式,探讨了构造活动的层序地层响应。构造活动控制层序界面的形成,一次逆冲末期的回弹隆升和下一次逆冲引起的变形是形成构造层序界面的主要原因。随着造山带前缘推覆的不断向前发展,前陆盆地的沉降中心和沉积中心向斜坡带方向迁移。构造层序的发育具有旋回性和阶段性,每一层序始于沉降速率迅速加快。

The sequence stratigraphy of continental foreland basins is an important domain in current research. The southern Junggar basin is a regenerated compound foreland basin resulted from two-phase superimposition. The sequences of the late phase foreland basin can be divided into 1 first-order sequence, 3 second-order sequences,5 third-order sequences and 15 fourth-order sequences in accordance with analyses results of outcrops, cores, seismic data, and well logs. Four systems tracts are recognized in each second-order sequences based on the cyclicity of tectonic and sedimentary evolution and the internal architectures of the sequences. The sequence stratigraphic model of southern Junggar foreland basin is established and sequence-stratigraphic responses to tectonics are discussed in this paper. Tectonic activity controls the formation of sequence boundary, which is formed mainly by the resilient uplift at the end of a thrusting and the deformation caused by the following thrusting. With continuous advancement of the orogenic belt front, the center of subsidence and depocenter of the foreland basin migrate toward the ramp region. The tectonic sequences are developed cyclically and periodically, and each sequence begins with a speeding up of subsidence.