龙门山前带中侏罗统近源冲积体系砂体展布与叠置模式

川西坳陷龙门山前带在中侏罗统沙溪庙组沉积时期，发育一套以冲积扇-辫状河三角洲为主的近源冲积体系。基于 高分辨率层序地层学理论，通过对野外露头、岩心、分析化验、地球物理和钻井资料的综合分析，阐明发育在山前带的近 源冲积体系的砂体成因类型，总结砂体垂向叠置关系和平面分布规律，建立近源冲积体系砂体叠置模式。结果表明，河道 和席化滩坝是研究区内主要的砂体成因类型，其中河道较为发育；物源和湖平面升降是影响砂体展布的重要因素，物源控 制河道砂体的展布，湖平面升降控制滩坝砂体的展布和河道砂体的质量；砂体叠置模式可以分为4种，分别是超低可容空 间叠置河道砂砾岩体、低可容空间叠置河道砂体、高可容空间叠置河道砂体和高可容空间河道叠置席化滩坝砂体。

Sand-body Distribution and Superposed Patterns of Alluvial Deposits in the Middle Jurassic in the Piedmont Zone of the Longmen Mountain Trust Belt

The Middle Jurassic Shaximiao Formation in the piedmont zone of the Longmen Mountain Trust Belt (LMTB) consists of a set of alluvial deposits, including alluvial fan and braided river delta. Based on the theory of high-resolution sequence stratigraphy, we studied sand-body types of alluvial deposits in the piedmont zone by a comprehensive analysis of outcrop profiles, seismic section, seismic amplitude image, core, and drilling data, summarized its vertical stacking patterns as well as horizontal distribution characteristics. The results show that channel and sheet-like bar constitute the main sand-body types and channels are generally well developed; Provenance and lake level changes are two important factors of sand-body distribution. Provenances affect sand-body distribution of channels and lake level changes affect sand-body distribution of sheet-like bar and physical property of channels; four types of sand-body superimposed patterns of different origins were classified, i.e., superimposed glutenite-body of channels in the ultra-low accommodation, superimposed sand-body of channels in the low accommodation, superimposed sand-body of channels in the high accommodation, and superimposed sand-body of channels and sheet-like bars in the high accommodation, respectively.