鄂尔多斯盆地本溪组潮汐-三角洲复合砂体沉积环境

摘要

Field outcrops and 45 boreholes were studied in order to reveal the depositional environment of sand bodies of the Upper Carboniferous Benxi Formation,and to understand the spatial distribution of favorable reservoir sandstone. A depositional model was reconstructed in reference to the sedimentary facies marks and the macro-distribution of sandstones of the Benxi Formation.It showed that the bidirectional cross bedding caused by tidal current and the one way cross bedding derived from river current coexisted in the Benxi Formation.The delta of Pangou Member was influenced by strong tidal action,the channel sand bodies were cut into isolated point bars and the delta lost its original macro-shape.The southern delta of the Jinci Member was also reformed by strong tidal action and resulted in tidal bars.The northern sand body of Jinci Member was affected moderately by the tidal energy and still retained the original delta shape.It was indicated that the depositional setting of Benxi Formation was a gulf of epeiric sea,the difference of tidal-river interaction controlled the distribution of sandstone. Therefore, the Carboniferous Benxi Formation is a tidal-delta complex facies associations and the effect of tidal current destroyed and redistributed the former delta.%为了揭示鄂尔多斯盆地东部上石炭统本溪组的沉积环境与有利储集砂体发育分布规律,本文在野外露头和钻井岩心观察的基础上,通过沉积相标志判别和砂体宏观分散体系刻画,建立了本溪组的沉积模式.本溪组具有潮汐成因的双向层理和河道牵引流成因的单向层理共存的特征;畔沟期的三角洲沉积作用弱,砂体规模小,强潮汐作用将砂体改造成补丁状,基本失去了原始三角洲的形态;晋祠期南部的三角洲沉积作用较弱,砂体规模中等,以强潮汐作用控制为主,被切割成孤立分布的潮汐砂坝群;晋祠期北部的三角洲沉积作用较强,中潮差背景下的河控砂体呈南北方向的条带状,规模最大,仍然保留了三角洲的形态;本溪期为开敞型陆表海湾环境,潮汐与河流相互作用的时空差异控制着本溪组砂体的发育分布规律.本溪组为潮汐砂坝-三角洲复合沉积体系,潮汐作用对先存三角洲砂体具有明显的破坏和再分配效应.