摘要： 构造活动是源-汇系统中形成古地貌和砂分散体系的重要影响因素。塔木察格盆地塔南凹陷在早白垩世是一个典型的断陷湖盆,经历了多期幕式断陷活动,但同沉积构造活动及其配置所产生的古地貌对层序结构特征、沉积体系及砂体分布的控制作用仍不明确。文中以地震、测井、岩心资料为基础,以层序地层学理论和古地貌控砂理论为指导,建立了塔南凹陷下白垩统层序地层格架;结合断层活动性分析,阐明了不同类型古地貌对沉积体系和砂体分布的控制作用和规律。构造演化和沉积充填的综合研究表明: 受控盆主断裂的幕式断陷活动及同沉积断裂的差异断陷活动影响,塔南凹陷发育横向凸起和走向斜坡2种类型的构造调节带,这些构造调节带是水系入盆的通道,控制着盆地的主体物源方向、沉积体系类型与分布特征;根据断层的几何形态及发育部位,共识别出4种类型构造坡折带,分别是陡坡断崖型坡折带、陡坡断阶型坡折带、缓坡反向断阶型坡折带和盆内坡折带,它们各自控制了不同类型沉积体系的形成与分布;沉积物入盆后,沉积物分散体系和砂体的分布特征受同沉积断裂的组合样式控制,研究区共发育梳状断裂系、叉状断裂系和平行断裂系3种同沉积断裂平面组合;与构造调节带相对应的断裂坡折带低部位是大型储层砂体,特别是低位扇三角洲或盆底扇砂体发育的有利部位,是寻找砂岩油气藏的有利区带。研究成果对于深化断陷湖盆源-汇系统理论、指导断陷湖盆砂体分布预测具有重要的理论意义和实际价值。

关键词: 同沉积构造活动, 构造调节带, 构造坡折带, 控砂机制, 下白垩统, 塔南凹陷

Abstract: The Ta'nan sag is a typical faulted lacustrine basin formed during the Early Cretaceous,which experienced multi-stage episodic faulting activities. Tectonic activities are an important factor for the formation of paleogeomorphology and sand distribution. However,the controls of paleogeomorphologies generated by synsedimentary tectonic activities on sequence architectures,sedimentary system and sand body distribution are still unclear. Based on seismic,well logging and core data,under the guidance of sequence stratigraphy theory and paleogeomorphic sand control theory,the sequence-stratigraphic frameworks of the Lower Cretaceous in the Ta'nan sag are established. Combined with the analysis of the major fault activity during different rifting stages,the controlling effects of different paleogeomorphologies on sedimentary system and sand body distribution are clarified. The investigation of the tectonic evolution and sediment fill of the Ta'nan sag during the Early Cretaceous suggests that the episodic rifting and various activities of major faults created complex paleogeomorphologies including transfer zones and structural slope-break zones,which significantly controlled the development and distribution of both depositional systems and sand bodies. The transfer zones including transverse uplift and relay ramp were the sites for drainage catchment,and controlled the locations of sedimentary provenances,entry points of sedimentary material into the basin,and the resultant development of depositional systems. According to fault geometry and the location of the slope-break zones,the structural slope-break zones of the Ta'nan sag during the climax rifting stage were subdivided into four types: fault scarp zone,fault terrace zone,gentle slope zone and intrabasinal fault break zone,which played significant roles in controlling the changes in accommodation and the distribution of depositional systems and sand bodies. Three syndepostional fault arrangement patterns were identified according to their distribution on the structural map,which are “comb-like”,“fork-like and “parallel”faults. Areas where the structural slope-break zone overlapped with transfer zones are sites for major drainage systems and the optimum locations of fan deltas and sublacustrine fans. The sand bodies deposited here are favorable targets for the exploration of litho-stratigraphic traps in the Ta'nan sag. The results have important theoretical significance and practical value for deepening the theory of source-to-sink system and guiding the prediction of sand body distribution in faulted lacustrine basins.

Key words: syndepositional faulting movement, transfer zones, structural slope-break zones, control mechanism of sand distribution, Lower Cretaceous, Ta'nan sag;

中图分类号: 

• P548