珠江口盆地白云凹陷中新统韩江组中上部层序结构及深水重力流沉积*

基于地震、测井资料的综合分析开展珠江口盆地白云凹陷中中新世韩江组中上部发育的硅质深水沉积的层序地层、沉积构成和古地理环境研究。韩江组中上部发育1个区域性的二级旋回(CSh),通过不整合面及相应的整合面进一步将该复合层序划分为6个三级层序。一系列陆坡峡谷以及侵蚀作用形成的水道是主要层序界面的重要识别标志,斜坡进积楔、扇朵体的底界面,测井曲线突变以及钙质超微化石的相对低值也可以帮助识别层序界面。盆地的不同位置上层序结构有差异,重力流沉积单元也不同。本次研究在斜坡识别出5种深水沉积单元: 浊流水道复合体、斜坡扇、陆坡峡谷、进积楔和半远洋—远洋沉积,在深海盆地识别出扇朵叶体。将浊流水道复合体划分为5种沉积单元: 滞留沉积、水道天然堤、滑塌及碎屑流沉积、侧向增生体和末期充填沉积。在陆坡、陆隆以及深水盆地分别识别出侵蚀水道、侵蚀加积水道和加积水道。

Sequence architecture and deep water gravity-flow deposits of the middle and upper member of Hanjiang Formation of Miocene in Baiyun sag,Pearl River Mouth Basin

The Middle and Upper Hanjiang Formation in the Pearl River Mouth Basin contains large scale siliciclastic deep-water,gravity-flow deposits. Gravity-flow deposits of the Middle and Upper Hanjiang Formation comprise a regional transgressive-regressive megacycle,which can be further classified into six sequences bounded by unconformities and their correlative conformities. A series of incised valleys or canyons and erosional-depositional channels are identifiable as marks of the major sequence boundaries which might have been formed as the result of global sea-level falls. Besides, prograding clinoform, bottom boundaries of fan lobes and relative low content of calcareous nannofossils are conducive to identification of sequence boundary. Not only the sequence architecture but also the depositional unit is different at various basin locations. Five gravity-flow depositional elements in the slope have been identified as follows: Turbidite channel complexes,lower slope fans,submarine canyon,prograding clinoforms and pelagic sediments. Turbidite channel complexes are divided into five depositional elements: Basal lags,channel and levee system,slumps,lateral accretion packages and telophase filling. Three types of channels are classified: Erosional,erosional-aggradational and aggradational,geometries of which changing along with gradient.