南沙群岛万安盆地构造演化史再探讨

南沙群岛万安盆地是位于南海西南海盆被动边缘上的张性沉积盆地。通过分析区域地球物理场特征及断裂分布，以及地震剖面的解释并结合钻井资料对比分析，在万安盆地新生代沉积中对比解释出T1，T2，T3，T4，T5，T6和Tg等7个地震反射界面。其中，Tg，T5和T3为3个区域不整合面的反射波，由这3个区域不整合面将盆地新生代沉积划分为3个构造层：Tg－T5，T5－T3和T3一海底。由此推测万安盆地在新生代经历过3次构造运动，因此其构造演化史经历了3个阶段：神狐运动（白垩纪未至古新世早期），南海运动（晚始新世至早渐新世）和万安运动（中中新世末）。从神狐运动到南海运动为万安盆地的奠基期，从南海运动至万安运动则是万安盆地的发展期，万安运动之后至今日是万安盆地的形成期。万安盆地的构造发育史和珠江口盆地东部的发展史相似，故推测它藏有丰富的油气资源。

A REDISCUSSION ON THE TECTONIC EVOLUTIONAL HISTORY OF THE WANAN BASIN IN NANSHA AREA

The Wanan Basin in Nansha area is a rifting basin located in the passive marin of the SW subbasin of the South China Sea. Through the characteristics of geophysical field and the distribution of faults, especially by interpretation of seismic profiles and contrdsting well data, we compared and interpreted seven reflected interfases, Tl, T2, T3, T4, T5, T6 and Tg, of which Tg, T5 and T3 represent three regional unconfondties and are the reflections of three tectonic movements in the Cenozoic sediments of Wanan Basin. According to the three regional unconformities the Cenozoic sediments can be subdivided into three tectonic layers: Tg-T5, T5-T3 and T3- seafloor. Therefore, we infer that there were three tectonic movements in Cenozoic in the Wanan Basin. So the tectonic evolutional history has experienced three phases: The Shenghu Movement (the end of Cretaceous-early Paleocene), the Nanhai Movement (lato Eocene- early Oligocene) and the Wanan Movement The Period from Shenghu Movement to Nanhai Movement was the foundational Phase while the Period from Nanhai Movement to Wanan Movement was the development phase in Wanan Basin. From the Wanan Movement to the present the regional subsidence in Wanan Basin occurred, which is the formation phase of Wanan Basin.The tectonic evolutional history of the Wanan Basin experienced three tectonic movements and three development phases, and is similar to the eastern part of the Zhujiang River Mouth Basin, so that we infer that there should exist rich oil and gasresources in the Wanan Basin.