Abstract: This study analyzed the sedimentary characteristics of shallow water deltic sand bodies grown with frequent changes of lake level,summarized their vertical superimposition relationship and areal distribution, and finally established their superimposition pattern,based on the theory of high resolution sequence stratigraphy,combined with a dataset consisting of seismic,logging,core and experiment data.Through analysis,we found that: ① distributary channels (CHs) and mouth bar-beach bar complexes are the main sand body types of the shallow water deltas in the Penglaizhen Formation.In the plan view,the distributary channels are mainly branch-shaped,distributing along the source direction,and MBCs are strip-shaped,parallel to the bank line;while vertically,sand bodies of different genetic types are superimposed into various types of composite sand bodies. ② As relief reduces gradually from the tectonically active margin to the basin, the stream energy decreases linearly with the gradient descent of the river system.Accordingly,the width and depth of the distributary channels of the shallow water delta decrease downwards.The low frequency lake level fluctuation controls the progradation and retrogradation of shallow water delta,whereas the change of high frequency lake levels determines the distribution and superimposition patterns of sand bodies of different genetic types. ③ The sedimentation evolution model of the Late Jurassic shallow water deltas in the foreland basin of Western Sichuan Depression was established,and four types of superimposition patterns for sand bodies there were classified,including superimposed low-accommodation channels, rivers over bar,superimposed high-accommodation channels and superimposed mouth bars.

Key words: shallow water delta, depositional model, distribution pattern of sand body, Jurassic, Sichuan Basin