贝尔凹陷贝西地区南屯组沉积相特征

通过对大量的岩心和测井、录井资料的研究,将贝尔凹陷贝西地区南屯组划分为4个三级层序(SQ_1-SQ_4),共识别出扇三角洲、辫状河三角洲、近岸水下扇、滑塌浊积扇、湖相等5个主要沉积相类型.研究区不同时期的沉积特征主要受构造演化的控制:SQ_1沉积时期,贝西地区为南北分割的沉积格局,主要发育扇三角洲、辫状河三角洲和湖泊相;SQ_2沉积时期湖平面进一步上升,统一的湖盆基本形成,沉积特征也与SQ_1沉积时期相似,但不同的是凹陷西南缘的物源区开始供给,形成新的扇三角洲;SQ_3沉积时期湖平面达到最大,扇(辫状河)三角洲沉积规模明显收缩,湖盆内以滑塌浊积扇沉积为主;SQ_4沉积时期构造活动增强,湖水面积萎缩,凹陷西北、北缘沉积体规模变化不大,但东南部物源供给不足,造成中东南部辫状河三角洲消失.

Sedimentary Fades of Nantun Formation in Beixi Area of Beier Sag

Based on lots of logging and core data, the Nantun formation in Beixi area of Beier sag (western Beier sag) is divided into four three-order sequences (SQ_1-SQ_4), among which five types of sedimentary facies are identified, i.e. fan delta, braided channel delta, neritic subsea apron, slump turbidite fan and lake ones. In this studied area, the sedimentary characteristics in different periods are mainly controlled by the tectonic evolution. In SQ_1 period, Beixi area is divided into south and north parts, dominated by fan delta, braided channel delta and lake facies; in SQ_2 period, continuous raise of the lake base level forms a unified lake basin with sedimentary characteristics like SQ_1, except for forming new fan delta in the southwestern margin of this sag for existence of provenance; in SQ_3 period, the lake base level reaches the highest with obvious shrinkage of sizes of the fan (braided channel) delta, dominated by slump turbidite fan; in SQ_4 period, the tectonic activities are active, causing shrinkage of the lake area and not big change of deposit sizes in northwester and northern margin of the sag except its southeaster part for insufficient provenance, which leads to the disappearance of the central and southeastern braided channel delta.