南苏丹迈卢特盆地北部凹陷古近系Yabus组浅水三角洲沉积特征

Sedimentary characteristics of Paleogene Yabus Formation in shallow-water delta in the northern sag of the Melut Basin,South Sudan

以南苏丹断陷湖盆迈卢特盆地为例,通过区域地质、岩心、测井、粒度及地震相等资料的分析研究,认为北部凹陷弱裂陷期形成的古近系Yabus组发育浅水三角洲沉积.受盆地裂陷活动与湖平面变化影响,Yabus组上段和下段具有不同的浅水三角洲沉积特征.Yabus组下段沉积时期,盆地构造活动弱,湖盆水体浅,以发育广泛分布的浅水三角洲平原分流河道为特征.Yabus组上段沉积时期,盆地裂陷活动增强,湖盆水体缓慢加深,形成了广泛分布的浅水三角洲前缘沉积及局部的滨浅湖沉积,水下分流河道、河口坝等砂体在断层配合下可形成构造—岩性圈闭,研究成果对迈卢特盆地北部凹陷的成熟探区滚动挖潜与精细勘探具有重要意义.

Taking the north sag in the Melut Basin in South Sudan as a case,researches were carried out based on regional geology,cores,logging data,grain sizes and seismic facies,which shows that the Paleogene Yabus Formation is shallow-water delta developed in the weak rifting period of the northern sag.And influenced by rifting activities and lake water level,the upper and lower members of the Yabus Formation have different sedimentary characteristics of shallow-water delta.During the sedimentary period of the lower member,basin tectonic activities were weak,and the lake water was shallow,so distributary channels of shallow-water delta plain were widely developed.During the sedimentary period of the upper member,rifting activities were intensive,and the lake water became deep,there developed widely distributed shallow-water delta frontal sediments and local coastal shallow lake sediments.The underwater distributary channels,distributary mouth bars and other sand bodies may form structural-lithologic traps controlled by faults.The research results are of great significance for continuously estimating the potential and finely exploring the mature exploration areas in the northern sag of the Melut Basin.