西非北部塞内加尔盆地白垩系陆源碎屑沉积体系及其控制因素

塞纳加尔盆地深水区白垩系广泛发育陆架三角洲及斜坡扇体系，是近期全球油气勘探发现最活跃的地区之一。通过地震相和井资料分析，对塞内加尔盆地陆架边缘斜坡带的层序格架、沉积-地貌演化，及其对构造、海平面和沉积物供应变化的响应关系开展了系统性的研究。研究表明盆地的白垩纪沉积充填可划分出以阿普特末期和塞诺曼末期区域性不整合面为界的2个复合层序CS1和CS2，进而划分出8个三级层序；识别出具有“源-汇”关系的陆架边缘三角洲和斜坡扇体系，并根据地震相划分出3种沉积亚相：三角洲平原，三角洲前缘和前三角洲，以及4种斜坡扇沉积单元：滑塌泥石流朵体、侵蚀-充填水道、前缘扇朵体和远端扇朵体；依据不同时期斜坡扇的演化特点（坡脚型—侵蚀型—宽缓型），划分出3个演化阶段。塞内加尔盆地白垩纪的沉积格局与物源供给、古地貌和海平面变化密切相关。斜坡扇的发育位置及三角洲的后期充填受古地貌的影响。海平面变化和沉积物供给控制着陆架三角洲和斜坡扇的推进和发育形态。西非毛里塔尼德的持续性构造隆升，中大西洋海底扩张增速，及早白垩陆缘翘倾等区域性构造事件，使塞内加尔盆地物源供给和古地貌发生变化。发育于陆架边缘的白垩纪三角洲-斜坡扇碎屑沉积体系构成了塞内加尔盆地最重要的油气勘探对象。

Sedimentary system of the Cretaceous terrigenous clastics and its controlling factors in Senegal Basin,northern West Africa

The Cretaceous system with its extensive shelf-edge deltas and slope fans in the Senegal Basin is one of the most active oil and gas exploration areas in the world.This study systematically explores the sequence framework and sedimentary-geomorphic evolution of the shelf-edge slope zone in the basin, and their responses to the tectonic, sea level and sedimentary supply variations based on the analysis of seismic facies and well data.The results show that the Cretaceous sedimentary system could be divided into two composite sequences (CS1 and CS2) separated by the regional unconformities of the Late Aptian and Late Cenomanian.The two sequences are subdivided into eight third-order sequences.The shelf-edge delta and slope fan facies with a source-to-sink relationship are identified.Three sedimentary subfacies are recognized in the deltas according to seismic facies, namely the delta plain, delta front and pro-delta; and four sedimentary units are identified in the slope fans, namely the landslide debris flow lobe, erosion-filling channel, delta-front fan lobe, and distal fan lobe.Three evolutionary stages are determined according to the evolutionary traits of the slope fan (from slope toe stage to erosional and wide and gentle stages).The deposition distribution of the Cretaceous is closely related to provenance supply, paleogeomorphology and eustatic fluctuation at different periods.The locations of the slope fans and the later filling in the deltas were once conditioned by paleogeomorphology.Sea level changes and provenance supply are the major factors controlling the shape and advancement of the deltas and slope fans.Regional tectonic events including the continuous uplift of the Mauritanides in West Africa, the expansion of mid-Atlantic seafloor, and the tilting of continental margin in the Early Cretaceous have changed the provenance supply and paleomorphology of the basin.The Cretaceous clastic sedimentary system with delta-slope fan facies developed on the shelf edge in the Senegal Basin is thus considered the most important target for oil and gas exploration in the study area.