南海晚中新世—上新世红河沉积体系研究

Research on Red River Sedimentary System of late Miocene-Early Pliocene,South China Sea

红河沉积体系为南海西北部近期新发现的大型远源沉积体系,其主要发育于南海莺歌海盆地和琼东南盆地。重点利用大量二维地震剖面资料,根据地震反射特征对晚中新世—上新世红河沉积体系的识别特征以及平面展布进行了研究,以此为基础划分了红河沉积体系在晚中新世—上新世演化阶段。研究结果表明:通过地震反射特征的分析,可以识别出三角洲、水下下切水道、海底峡谷、水道堤岸复合体以及海底扇朵体等沉积;依据红河沉积体系的平面组合和展布特征,可将晚中新世至上新世的红河沉积体系演化划分为3个阶段:10.5～5.5 Ma(SQ1、SQ2)为红河海底扇发育阶段,以发育大型"三角洲—水下下切水道—海底扇"为特征;5.5～3.6 Ma(SQ3、SQ4)为限制性海底扇—中央峡谷发育阶段,以先发育限制性海底扇,后发育大型海底峡谷为特征;3.6～1.8 Ma(SQ5、SQ6)为红河沉积体系衰弱阶段,在研究区内以红河沉积体系主体不发育,海南岛陆坡发育为特征。红河沉积体系是青藏高原隆升的产物,研究红河沉积体系除有利于制定油气勘探方向外,还有助于青藏高原隆升历史恢复、红河袭夺等问题的研究。

In the northwest of South China Sea, a huge far source Sedimentary System which is called Red River Sedi- mentary System has been discovered recently. The Red River depositional system refers to ＂a genetically related com- bination of a series of deltas, submarine canyon infiUings, submarine fans and fine-grained suspension deposits deri- ving from the terrestrial clastics of the Red River in Neocene＂. The main body of this depositional system comprises the Red River delta, the Red River submarine fan and the Central Canyon. In order to understand the identify stand- ard and distributing in the plan view, a great deal of 2D seismic profiles has been used. The paper mainly focuses on the system which is developed during late Miocene to Pliocene. Base on the distributing in the plan view, the develop- ment history of the Red River Sedimentary system can be understood. The results show that deltas, channels, subma- rine canyon, channel-levee complex and lobes can be identified in the Red River Sedimentary system based on the seismic reflection characteristics. According to the combination and spatial distribution features of the Red River sedi- mentary system, the development history of the system can be subdivided into three stages： SQ1-SQ2, the formation period of Red River submarine fan, which is characterized by huge submarine fan ; SQ3-SQ4, the development period of the confined submarine fan-Central Canyon, which is characterized by a confined submarine fan developed before the central Canyon; and SQ5-SQ6,the weakening period of the Red River depositional system, which is characterized by Red River Sedimentary System fading out in the research area, instead of Hainan slope~ growing. Red River Sedi- mentary System derives from Qinghai-Tibetan Plateau uplift. The research is not only beneficial for ascertaining Oil and gas prospecting, but also helpful for rebuilding uplift history of Qinghai-Tibetan Plateau, and answering the ques- tion whether Red River capture occurred or not.