南海西缘中新世构造事件的沉积响应--以万安盆地为例

Sedimentary responses of tectonic events in Miocene,western margin of South China Sea:a case study of Wan’an Basin

万安盆地位于南海西南陆缘,独特的构造位置使得其充填演化成为研究西南次海盆扩张、西缘走滑断裂活动的重要窗口。利用已有钻井资料,通过井震对比和地震相分析,探讨万安盆地中新世沉积充填特征及其对南海西缘构造事件的沉积响应。研究表明,中新世万安盆地主要发育三角洲、浊积扇、碳酸盐台地和生物礁等4种与油气储层关系密切的沉积相类型。早中新世时期,以三角洲体系为主;中中新世时期,三角洲仅发育于盆地西部,同期盆地东部开始发育碳酸盐台地;晚中新世时期,源自盆地西部的浊积扇开始发育。早中新世末南海西南次海盆停止扩张及中中新世末南海西缘走滑断裂活动,形成了2个重要构造不整合界面,对万安盆地中新世沉积充填具有重要的控制作用。

The Wan’an Basin is located on the southwestern margin of the South China Sea,and its unique tectonic position has made its filling evolution an important window to study the expansion of the southwest submarine basin and the strike-slip faults on the western margin.Based on the results of core analysis,correlation of core and seismic reflections,and seismic facies,the characteristics of the infilling of the Wan’an Basin and the sedimentary responses to tectonic events in Miocene were studied.Four main sedimentary facies related to hydrocarbon reservoirs have been developed in the basin during Miocene,including delta,turbidite fan,carbonate platform and reef.In the Early Miocene,delta facies was widespread in the study area.During the Middle Miocene,delta facies developed only in the western part of the Wan’an Basin,and carbonate platform deposits began to develop in the eastern part.And turbidite fan,sourced from the western part,began to develop in the Late Miocene.The southwestern sub-basin of the South China Sea stopped expanding at the end of the Early Miocene and the strike-slip fault activities on the western margin of the South China Sea at the end of the Middle Miocene formed two important tectonic unconformity interfaces,which played an important role in constraining the Miocene sedimentary filling in the Wan’an Basin.