苏丹Muglad盆地Fula坳陷白垩系Abu Gabra组层序地层及沉积体系

Lower Cretaceous Sequence Stratigraphy of Fula Depression,Muglad Basin,Sudan

Fula坳陷白垩系Abu Gabra组是Muglad盆地第一裂谷旋回中形成的同裂谷期地层,它可以分为3个二级层序,自下而上是K1SSⅠ、K1SSⅡ和K1SSⅢ,它们分别与断陷期早期地层、断陷期中期地层和断陷期晚期地层相对应。其中二级层序K1SSⅠ和K1SSⅢ各分为2个三级层序,K1SSⅡ则可进一步划分为3个三级层序。综合应用地震和钻/测井资料,以三级层序为单元,完成了AbuGabra组沉积相分布与沉积体系预测工作。研究认为,阿加组的主要沉积类型包括:河流相、三角洲相、扇三角洲相、辫状河三角洲相、近岸水下扇相、滨浅湖亚相、半深湖—深湖亚相。各沉积相带在Fula坳陷内的演化形成了5个主要沉积体系,分别是东北部的扇三角洲体系,西北部的三角洲体系、西部近岸水下扇体系、东南部辫状河三角洲体系以及早期的河流沉积体系。沉积体系的分布与演化受构造活动强度变化的控制,也受古地形和古地貌的影响。

Abu Gabra Formation of Cretaceous Fula depression, which is formed during the first rifting cycle, can be divided into three second-order sequences, namely, sequence K1SSI, sequence K1SSⅡ and sequence K1SSⅢ. They can correspond separately to the strata deposited in the early, middle and late rift period. Of the three second-order sequences, the sequence K1 SSⅠ and sequence K1SSⅢ can be subdivided into two third-order sequences, the sequence K1SSⅡ into three third-order sequences. Based on the integrated analysis of seismic data, core and well logging, the distribution of sedimentary facies and the prediction of sedimentary system are achieved. Through investigation, 7 types of sedimentary facies are recognized, namely, fluvial deposit, delta, fan delta, braided delta, proximal sublacustrine fan, lacustrine facies. Due to the evolution of their sedimentary facies, five chief depositional systems are established in the Fula depression. They are fan delta system in the NE, delta system in the NW, proximal sub-lacustrine fan in the west, braided delta system in the ES and fluvial system produced in the early period. The distribution and evolution of the depositional systems is controlled by tectonics, probably influenced by paleotopography and paleogeography.