琼东南盆地中中新世重力流海底扇沉积特征及控制因素

Sedimentary features and controlling factors of the gravity flows in submarine fan of Middle Miocene in the Qiongdongnan Basin

以往研究认为琼东南盆地陆架坡折形成于中新世末期,而在中新世早中期盆地北部为古斜坡地形。通过对琼东南盆地中新统坡折带、区域海平面、三角洲与重力流海底扇沉积的关系分析,结合钻井、地震等资料确定了琼东南盆地中中新世海底扇沉积特征及控制因素。结果表明,在中新世早中期盆地北部发育沉积、断裂和挠曲3种类型坡折,海底扇的沉积分布主要是受到沉积坡折控制,尤其是10.5Ma区域海平面下降时期,陵水凹陷、乐东凹陷发育早、晚2期大型富砂海底扇,早期海底扇沉积在陵水凹陷,浊积水道迁移快,数量多但下切作用不强;晚期海底扇沉积在乐东凹陷,浊积水道稳定分布,数量少,下切明显,朵叶体平面呈扇形分布,海底扇水道和朵叶体是有利的沉积单元。

Previous research showed that shelf slope break zone in Qiongdongnan Basin was formed at the end of Miocene,while paleo-slope was developed in the northern Basin at the early-middle period of the Miocene.Based on the analysis of the relationship of Miocene slope break zone,regional sea level,delta,and gravity flows,sedimentary features and controlling factors of the gravity flows were concluded with drilling and seismic data.The research showed that sedimentary,fault and flexure slope breaks were developed in the northern Basin at the early-middle period of the Miocene,and sedimentary break zone had an important effect on the distribution of the gravity flows.When regional sea level falling at 10.5Ma,Ledong Sag and Lingshui Sag developed large-scale and sand-rich submarine fans,which could be divided into two periods.Lingshui Sag developed early submarine fans,where turbidite channels moved quickly with large number and weak incision.Ledong Sag developed terminal submarine fans,where turbidite channels distributed stably with smaller amount and strong incision,and lobes bodies＇ morphology appeared flabellate.Turbidite channels and lobes bodies of submarine fans were the favorable sedimentary units.