川北前陆盆地上三叠统须家河组陆相层序地层

中国中西部前陆盆地大多具有陆内俯冲造山形成的特点,层序地层学在这类前陆盆地中的应用是一个值得研究的新领域。对川北前陆盆地上三叠统须家河组5条露头剖面和1条测井剖面进行详细沉积相分析和层序地层划分,同时阐述了沉积相迁移规律、层序界面类型、层序发育特征及基准面变化;将川北前陆盆地上三叠统须家河组划分为4个三级层序(TS1,TS2,TS3和TS4)。大竹、开江一带须家河组沉积厚度为400～600m,4个层序发育完整;向北东至万源一带地层变薄至100余m,保存残留不全的须家河组只能归为1个三级层序(TS4)。在露头剖面和测井剖面层序地层划分的基础上建立的层序地层格架表明:TS1—TS2以曲流河及曲流河三角洲沉积体系为主,盆地处于稳定坳陷和慢速充填的欠补偿状态,TS3—TS4以冲积扇、辫状河及辫状河三角洲沉积体系为主,盆地处于强烈坳陷和快速充填的过补偿状态。沉积相的时空叠置样式受北部秦岭造山带构造活动的制约作用较为明显。

Continental Sequence Stratigraphic Research of the Upper Triassic Xujiahe Formation, Northern Sichuan Foreland Basin, China

The foreland basins of central-western China are mostly characterized by intracontinental-subduction,so the application of sequence stratigraphy to these basins is a new research field.Sedimentary facies analysis and sequence stratigraphic division of five measured outcrop sections and one well log arecarried out in detail.The patterns of sedimentary facies transformation,the types of sequence boundaries,sequence characteristics and the related base level changes are described as well.The result suggests that the Upper Triassic Xujiahe Formation of the northern Sichuan foreland basin be divided into four third-order sequences(TS1,TS2,TS3 and TS4).The thickness of Xujiahe Formation is about 400-600 m in Dazhu-Kaijiang basin where the four sequences are relatively complete.In contrast,the Xujiahe Formation tends to thin westward to less than 100 m in Wanyuan area where only one sequence could be recognized.Sequence stratigraphic framework is constructed based on the above sequence stratigraphic division of the six sections.TS1-TS2 is dominated by meandering river and delta depositional system,which implied stable subsidence and an underfilled basin.In contrast,TS3-TS4 is characterized by alluvial fan and braided river depositional system,which showed strong subsidence and an overfilled basin.The spatial and temporal distribution of sedimentary facies and stacking patterns were restrained and controlled by tectonics of northern Qinling orogenic belt.