孟加拉湾若开陆缘晚中新世以来渐进式深水水道形态-沉积演化及其源-汇成因  

The gradual change in morphology and architecture of submarine channels in the Rakhine margin,Bengal Bay since the Late Miocene and its source-to-sink genesis

作　　者：朱一杰 龚承林[1,2] 邵大力 齐昆 陈燕燕 丁梁波 马宏霞 ZHU Yijie;GONG Chenglin;SHAO Dali;QI Kun;CHEN Yanyan;DING Liangbo;MA Hongxia(College of Geosciences,China University of Petroleum(Beijing),Beijing 102249,China;State Key Laboratory of Petroleum Resources and Prospecting(China University of Petroleum(Beijing)),Beijing 102249,China;PetroChina Hangzhou Research Institute of Geology,Hangzhou 310023,China)

机构地区：[1]中国石油大学(北京)地球科学学院,北京102249 [2]油气资源与探测国家重点实验室(中国石油大学(北京)),北京102249 [3]中国石油杭州地质研究院,浙江杭州310023

出　　处：《地学前缘》2023年第4期182-195,共14页Earth Science Frontiers

基　　金：国家自然科学基金项目(41972100)。

摘　　要：深水水道是当前深水沉积学研究的前沿,多期水道往往无序迁移、无规律演化;研究发现孟加拉湾若开海域深水水道的沉积构成和形态特征自晚中新世以来呈现渐进式演化过程,其成因机制有待进一步研究。在沉积特征上,从晚中新世至今若开海域深水水道呈现渐进式的演化过程:天然堤越来越发育,水道侵蚀下切作用越来越弱。具体来说,晚中新世以两翼不发育堤岸的无堤岸水道为主,以侵蚀作用为主;上新世无堤岸水道和堤岸水道兼而有之,侵蚀作用和沉积作用兼而有之;而第四纪主要发育堤岸水道,以沉积作用为主。在形态特征上,从晚中新世至今若开海域深水水道亦呈现渐进式演化的特点:下切规模越来越小,平面弯曲度越来越大。具体来说,晚中新世水道下切规模较大,水道宽且深,横截面积大,弯曲度小;上新世水道下切规模相对减小,水道宽度、深度、横截面积及弯曲度适中;第四纪水道下切规模较小,水道窄且浅,横截面积小,弯曲度大。研究表明晚中新世至今渐进式深水水道形态-沉积演化是布拉马普特拉河沉积物分散路径自晚中新世以来渐进式迁移演化的源汇响应。伴随着布拉马普特拉河沉积物分散路径渐进式向西迁移,靠东一侧的研究区盆外供源沉积物渐进式减少,重力流发育程度亦渐进式衰减,从而导致深水水道的形态特征和沉积构成也呈现渐进式演化。Submarine channels are a frontier topic in deepwater sedimentology.Multi-stage channels usually migrate and evolve nonuniformly.Submarine channels in the Rakhine Basin,however,exhibit a gradual change in their geomorphology and architecture since the Late Miocene.The genesis of such gradual change is poorly understood.In this study we conducted 3D seismic investigation into the geomorphology,sedimentary characteristics,genesis and evolution of the Rakhine submarine channels.Architecturally,the Rakhine submarine channels show a gradual increasing of levee development and decreasing of undercutting.Specifically,Late-Miocene channels lack overbank levees,and erosion is predominant.Pliocene channels are characterized by mixed leveed and non-leveed channels and concurrence of deposition and erosion.Whilst Quaternary channels are flanked by extensive levees,and channel deposition is predominant.Morphologically,the Rakhine submarine channels display a gradual decreasing of erosion scales but a gradual increasing of sinuosity.Specifically,Late-Miocene channels exhibit large-scale undercutting,and are wide and deep,with a large cross-section but low sinuosity.Pliocene channels are characterized by moderate erosion,channel size and sinuosity.In comparison,Quaternary channels show reduced undercutting and channel size,but higher sinuosity.Such gradual change in channel morphology and architecture can be attributed to the gradual,westward migration of the Brahmaputra River sediment-routing system since the Late Miocene which led to gradual decreasing of extra-basinal sediment supply and subsequent development of gravity flows to bring the observed changes in submarine channels.

关 键 词：孟加拉湾 深水水道 形态特征 沉积构成 渐进式演化 源-汇成因 

分 类 号：P512.2[天文地球—地质学] P618.13