南海北部琼东南盆地中央峡谷体系沉积演化

Sedimentary evolution of the central canyon system in Qiongdongnan Basin,northern South China Sea

基于琼东南盆地二维和三维地震资料,对中央峡谷体系的形态特征和内部充填结构进行了描述和解剖,指出中央峡谷体系的"分段性"和"多期次性"特征。通过对该大型轴向峡谷体系在不同部位和不同演化阶段的差异性对比,结合晚中新世以来琼东南盆地构造—沉积条件的变化,将琼东南盆地中央峡谷体系的沉积演化划分为4个阶段,分别是晚中新世的峡谷蕴育阶段、上新世早期峡谷的侵蚀-充填阶段、上新世晚期峡谷的平静充填阶段和更新世以来峡谷的"回春"阶段。研究表明,晚中新世早期(11.6 Ma)盆地东部的区域性构造变革事件促使了峡谷雏形的形成;上新世早期西北部和北部充足的沉积物供给、南部隆起的遮挡和东部地貌特征等因素控制了中央峡谷体系自西向东的发育,并将该峡谷限制在琼东南盆地的中央坳陷带内;上新世晚期沉积条件的变化,导致峡谷只在盆地东部发育;更新世以来的气候因素和盆地东部的地貌特征共同控制了中央峡谷体系在更新世的"再次繁盛"。

In order to further understand the central canyon system （CCS） in Qiongdongnan Basin （QDNB）, a large axial submarine canyon, the present study described and dissected morphological characteristics and internal architectures of the CCS based on 2D and 3D seismic data, and the result indicated that the CCS in QDNB can be characterized by ＂segmentation＂ and ＂multi phases＂. Based on integrated comparisons and analyses of different segments and evolution phases of the CCS and combined with changes of tectonic- sedimentary conditions of QDNB, we could divide the sedimentary evolution of the CCS into 4 phases, i.e. an initial development phase in Irate Miocene （11.6 Ma 5.7 Ma）, an eroded-infilling phase in Early Pliocene （5.7 Ma-3.7 Ma）, a tranquil infilling phase in Late Pliocene （3.7 Ma-1.81 Ma） and a rejuvenation phase since Pleistocene （since 1.81 Ma）. The regional tectonic transformation at late Middle Miocene （11.6 Ma） initiated the formation of an axial sub basin in the eastern QDNB, which can be regarded as a rudi ment of the CCS. In Early Pliocene, abundant sediments supplied the basin from the northwestern and northern sources, and the limitation from the southern uplift belt and the geomorphology of the eastern QDNB would constrain the developing course of the CCS from west to east and confine the canyon within the central depression belt. Because of the lack of deposits during Irate Plio cene, the CCS then only developed in the eastern QDNB. Climate factors, a distributary effect of the northern seamount and the to- pography of the eastern QDNB have co-controlled the development of the modern central canyon system since Pleistocene, which is called as a rejuvenation phase of the CCS.