珠江口盆地阳江东凹裂陷期沉积环境及其构造控制

Syn-rifting Sedimentary Environment and its Tectonic Control in the Eastern Yangjiang Sag of the Pearl River Mouth Basin

珠江口盆地阳江东凹形成于古近纪裂陷期,广泛发育烃源岩的富存层段——文昌组、恩平组,具有陆相断陷盆地沉积以及构造控制下多幕演化的特征。沉积环境演变以及构造-沉积的耦合作用是陆相断陷盆地的重要研究方向,认识其动态过程可为烃源岩识别和油气评价建立基础。本文从三维地震资料、钻井资料入手,通过地震反射特征和井震联合分析,划分了研究区的层序地层格架,识别出文昌组、恩平组的地震相类型。根据地震相类型和岩性资料,认为裂陷期文昌组、恩平组发育7种沉积相,洼陷中心发育半深湖相、滨浅湖相、湖底扇相,洼陷边缘在不同时期因构造、物源的影响,不同程度地发育扇三角洲相、辫状河三角洲相、近岸水下扇相、滩坝相,构成完整的沉积体系。沉积期间,构造活动尤其是控洼断裂的活动对沉积产生重要的影响,总体分为初始裂陷阶段、强烈裂陷阶段、裂陷萎缩阶段三个阶段的演化,由此,阳江东凹为该三个阶段演化的产物。

The widespread source rocks of the Wenchang and Enping Formations in the eastern Yangjiang Sag of the Pearl River Mouth Basin were deposited in a faulted lacustrine basin during the Paleogene rifting period,and are characterized by multi-stage structure controlled sedimentation.Evolution of sedimentary environment and coupling of tectonics and sedimentation are important factors to decipher the dynamic processes of a faulted basin and helpful for source rock identification and hydrocarbon evaluation.The stratigraphic sequences in the study area were divided and the seismic facies types of the Wenchang and Enping Formations were identified based on 3D seismic reflection data and drilling data.According to the seismic facies types and lithology,seven syn-rifting sedimentary facies that constitute a complete sedimentary system have been recognized in the Wenchang and Enping Formations,which include the semi-deep lacustrine facies and offshore shallow lacustrine facies developed in the center of the sub-sag,and fan delta,braided river delta,near-shore sub-lacustrine fan and lake beach bar developed in the edge of the sub-sag.The tectonic activities,especially those of the sub-sag-controlling faults,influenced the sedimentation significantly.The tectonic evolution of the eastern Yangjiang Sag can be divided into three stages,including initial,intensive and weak rifting.