川西坳陷上侏罗统浅水漫湖沉积特征与砂体叠置模式

Sedimentary characteristics and sand-body superposed patterns of flood-overlake deposits of the Upper Jurassic in Chuanxi Depression

川西坳陷在上侏罗统蓬莱镇组沉积期,地形平缓、气候干旱,湖平面频繁变化,发育了一套以浅水三角洲—漫湖为主的沉积体系。基于高分辨率层序地层学理论,通过对野外露头、岩心、分析化验和钻井资料的综合利用,阐明了发育在湖平面频繁变化背景下的浅水漫湖沉积特征,总结了砂体垂向叠置关系和平面分布规律,建立了浅水漫湖沉积体系砂体叠置模式。(1)分流河道和滩坝是研究区内浅水漫湖沉积体系的主要微相类型;(2)分流河道垂直于湖岸线分布,滩坝平行于湖岸线分布,在高频层序发育过程中,由于湖浪淘洗、河流进积等因素的改造,浅水漫湖沉积砂体经历了沉积—破坏—再沉积的过程,在平面上表现为分流河道切割多期平行于湖岸线的滩坝砂;(3)多种成因砂体叠置模式可以分为4种,分别为同期同相自旋回叠置模式、同期异相自旋回叠置模式、不同期同相异旋回叠置模式和不同期不同相异旋回叠置模式。

The Upper Jurassic Penglaizhen Formation in Chuanxi Depression is a set of flood-overlake deposits at low angular ground, under arid climatic condition and with lake level frequently fluctuating. Based on high-resolution sequence stratigraphy, we analyzed the sedimentary characteristics of flood-over- lake deposits by integrating outcrop, core, experiments and drilling data, summarized its vertical stacking as well as horizontal distribution patterns, and the sand-body superposed patterns of flood-ouerlake were constructed. （1） Distributary channels and beach bars constitute the main facies types in the study area;（2） Distributary channels stretched vertical to the lake shoreline, while beach bars developed along the lake shoreline, with the formers constantly cutting through phases of the latters from alternating destruction and sedimentation by wave erosion and debris progradation into the lake, during development of high-fre- quency sequences ; （3） Four types of sandbody superimposed patterns of different origins were classified, namely same time same facies autogenic type, same time different facies autogenic type, different time same facies allogenic type and different time different facies allogenic type.