下刚果盆地南部盐上地层重力滑脱变形演化特征

Characteristics of gravity glide deformation developed in post-salt layer,southern part of lower Congo basin

为解析下刚果盆地南部深水区盐上地层油气成藏的地质背景,基于三维地震资料研究下刚果盆地南部盐上层系的重力滑脱变形的过程,总结重力滑脱变形的特征.结果表明:下刚果盆地南部盐上地层重力滑脱构造变形体系是沉积地层在陆缘掀斜条件下,沿阿普特期盐岩层滑脱的结果,在阿尔布末期—晚白垩纪、中渐新世—现今两个时期内强烈活动,其他时期活动强度较弱.滑脱变形形成一系列在陆缘规律分布的变形构造,前缘发育伸展变形,后缘发育挤压变形,前缘地层的向前滑脱和压缩变形为后缘伸展提供补偿空间.受平面沉积负载与盐下滑脱面形态的影响,地层滑脱变形强度与变形方式具有明显的平面差异.随着沉积物向海进积,在晚期滑脱过程中地层伸展作用向前扩展,挤压作用向前后两个方向扩展,晚期挤压作用向后扩展造成先存伸展变形的挤压反转.盐体卷入到上覆地层的滑脱变形,盐岩抽空造成地层塌陷,形成相应的次级沉积中心与断裂组合,构成有利的油气圈闭.若强度适中且与烃源岩排烃史有效配合,局部构造反转有利于油气成藏.

In order to understand the geological background of petroleum entrapment in southern part of lower Congo basin in deepwater areas,the evolution of gravity gliding system developed in post-salt layer has been analyzed and the character of strain system are summarized based on 3-D seismic data.The strata overlying salt glide on inclined configuration,imposed by gravity,was generated into gliding system.The high strain periods are Aptian-late Cretaceous,middle Oligocene-recent,other periods are characterized by low strain rate.The strata glided into a complex of structure distributed in continental margin with extension in back zone and compression in front zone.Frontal strata's transition and compression strain provide compensated room for extension strain in back zone.Horizontal gliding degree are differentially affected by sedimentary load and configuration of gliding surface.The extension strain advanced seaward,the compression strain advanced toward continent when the compensated room generated by transition and glide of frontal strata is outstripped by the extension strain during late strain period,resulting in inversion tectonic.Salt flow was involved in gliding stain,and fault array and depocentres are generated when salt withdraw from origin layer,excellent traps are formed at the same time.It is favorable for petroleum entrapment if the tectonic inversion is well coupled with source rock expulsion history.