南海南部北康盆地晚中新世以来深水沉积单元时空分布特征及其控制因素

Spatiotemporal distribution characteristics and controlling factors of deep-water sediments in the Beikang Basin since the Late Miocene,southern South China Sea

南海南部北康盆地是我国海域油气研究的重点区域,前人对该区域沉积地层的研究集中在古近系烃源岩和中中新世碳酸盐岩储层,有关晚中新世以来深水沉积发育及分布特征的研究仍很薄弱。为此,研究用2D地震数据资料识别北康盆地晚中新世以来沉积单元,揭示深水沉积单元分布特征及其控制因素。基于地震反射特征,研究识别了北康盆地晚中新世以来的主要沉积体类型,包括披覆沉积、块体流沉积和浊流沉积,其中浊流沉积可进一步分为限制型浊积体和三角洲前缘浊积体。披覆沉积在北康盆地前隆区域大面积发育,沉积厚度从南向北递减。块体流沉积则主要分布在研究区隆后盆地,厚度自西南向东北递减。结果表明北康盆地晚中新世以来的深水沉积受到物源供给、地形、构造活动和海平面变化的控制。其中,物源供给是控制研究区沉积体发育位置和厚度变化的主要因素。地形对重力流沉积(块体流沉积和三角洲前缘浊积体)和半远洋沉积的分布范围进行控制。研究成果可为深水沉积发育及其控制因素研究提供理论依据。

The Beikang Basin,located in the southern South China Sea,is a significant area for offshore oil and gas exploration in China.Previous studies in this region have primarily focused on the Palaeogene source rock and the Middle Miocene carbonate reservoirs,neglecting the investigation of deep-water sediments since the Late Miocene.Therefore,this study aims to explore the spatiotemporal distribution,characteristics,and controlling factors of deep-water sediments in the Beikang Basin since the Late Miocene,utilizing 2D seismic data.Three types of sedimentary deposits have been identified in the Beikang Basin since the Late Miocene:draping strates,mass-transport deposits(MTDs),and turbidites.Turbidites can be further classified into confined turbidites and delta-front ones.The study reveals that the draping state is predominantly developed in the forebulge tectonic regions of the Beikang Basin,with a decreasing thickness from South to North.MTDs,on the other hand,are mainly distributed in the Backbulge zone,with a thickness that decreases from Southwest to Northeast.The findings indicate that the development and distribution of sediments in the Beikang Basin are influenced by various factors,including sedimentary supply,geomorphic features,tectonic activity,and eustatic sea level changes.The location and thickness of deep-water sediments are primarily controlled by the supply of materials.Additionally,the distribution range of gravity flow deposits and draping states is influenced by the topography of the area.These results provide a theoretical foundation for understanding the development and controlling factors of deep-water sediments in the Beikang Basin.