关键词: 近源冲积体系, 砂体成因类型, 砂体分布规律, 龙门山前带, 沙溪庙组, 侏罗系

Abstract: 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.

Key words: alluvial deposits, sand-body type, sand-body distribution, the piedmont zone of the Longmen Mountain Trust Belt;
Shaximiao formation, Jurassic