南海北部盆地新生代物源对周边主要河流演化的响应

Sedimental provenance response in the northern South China Sea to the Cenozoic fluvial evolution

源汇系统(Source-to-sink system)是将物源区的构造剥蚀、沉积物输送区的沉积物搬运和沉积区的沉积物堆积等视为一个完整系统。沉积物的源区恢复和附近水系重建是源汇研究的热点问题,沉积物碎屑锆石U-Pb定年是源汇系统研究的有效方法之一。南海北部与其周边地区构成了一个完整的源汇系统,通过源汇分析可获得南海北部各盆地沉积物来源及周边主要河流的演化历史。本文通过总结前人在南海北部主要盆地新生代沉积物碎屑锆石U-Pb研究成果,探讨珠江、红河和昆莺琼古河的新生代演化历史。珠江最早的支流北江和东江形成于早渐新世,晚渐新世溯源到西江上游的红水河、左江和右江,中新世溯源到西江中游柳江、桂江和上游的北盘江、南盘江。在晚白垩世—古近纪红河属于青藏高原东缘大型向东南或向南流河流的一部分,之后由于地貌变化形成现今红河。昆莺琼古河在早渐新世开始发育影响到珠江口盆地,在晚渐新世昆莺琼古河雏形已经基本形成,中新世起昆莺琼古河可能向西有一定程度的退缩。

Source-to-sink system includes tectonic denudation,sedimentary transport and sedimentary deposition.The sedimentary provenance and paleo-river reconstruction are the hot scientific issues,and sedimentary detrital zircon U-Pb dating is one of the effective methods for deciphering the Source-to-sink system.The northern South China Sea and its surrounding areas constitute a complete Source-to-sink system.Therefore,the analysis of Source-to-sink system can be used to decipher the sedimentary provenance of the marine basins and the evolution history of major rivers close to the northern South China Sea.In this paper,we discuss the Cenozoic evolutionary history of the Zhujiang,the Red River and Kontum-Ying-Qiong River by summarizing previous studies on the detrital zircon U-Pb ages from Cenozoic sediments in the northern South China Sea.The Pearl River formed its tributaries of Beijiang and Dongjiang rivers during the Early Oligocene,and traced to Hongshui River,Zuojiang and Youjiang during the Late Oligocene,and then formed the present-day tributaries with Liujiang,Guijiang,Beipan River and Nanpan River since Miocene.The Red River belongs to the large south-flow river system in the southeastern Tibetan Plateau before Late Cretaceous-Paleogene,then the present Red River formed by the subsequent landscape change.The Kontum-Ying-Qiong river was formed during the Early Oligocene,and its prototype was basically formed during the Late Oligocene,and then it may have retreated westward to a certain extent since the Miocene.