塞内加尔盆地北部次盆白垩系被动大陆边缘深海扇演化特征及主控因素

Evolutionary characteristics and controlling factors of deep-sea fans in Cretaceous passive continental margin basin,Northern Subbasin,Senegal Basin

被动大陆边缘深海扇是当今海洋深水油气勘探的热点。识别深海扇,明确其时空演变特征,总结关键地质因素对其发育的控制作用,对于建立深海扇成因与预测地质模型具有重要意义。本文通过地震与钻井资料综合解释,分析塞内加尔盆地北部次盆白垩纪被动大陆边缘时期的构造-沉积演化特征,识别深海扇体,并分析其岩性、形态与规模的演变特征;然后分析海平面变化、陆源物质供给、陆坡与沟谷地貌等地质条件对深海扇体发育的控制作用。研究表明,研究区在白垩纪盆地被动大陆边缘阶段,经历了早白垩世的碳酸盐岩台地建设期、Albian-Santonian期碎屑岩沉积被陆坡内外分割的沉积期、Campanian-Maastrichtian期的碎屑岩缓坡沉积期等3个构造-沉积演化阶段;从早白垩世Aptian期到白垩纪末期发育了具有不同岩性、形态与规模特征的深海扇体。全球海平面变化、陆源碎屑供给、陆坡与沟谷地貌特征共同制约了深海扇的演化特征,但它们对深海扇发育与演化的影响作用又有所不同。全球海平面变化与陆源碎屑供给特征更多是影响了扇体的岩性粗细与规模,而陆坡沟谷地貌特征则直接决定了扇体的形态与分布。

Deep-sea fan reservoirs in passive continental margin basins are among exploration hotspots in offshore petroleum exploration.Understanding the spatiotemporal evolution of deep-sea fans can help refining geological models by enhancing the exploration and development of related reservoirs.Based on seismic and drilling data,different types of deep-sea fans with characteristic lithologies,shapes,and sizes are identified along the passive continental margin of the Senegal Basin.Factors such as sea-level changes,sediment supply,and paleo-geomorphology were integrated into the interpretation.This study shows that the passive continental margin dates back to the Middle Jurassic.During the Cretaceous Age,the study area underwent three stages of tectonic-sedimentary evolution:(1)carbonate platform build-up stage during the Neocomian and Aptian Ages;(2)sedimentary stage of clastic deposition on a continental fault-slope from the Albian to Santonian Ages;and(3)sedimentary stage of clastic deposition on a gentle continental slope(slope-break)during the Campanian and Maastrichtian Ages.During these periods,five types of deep-sea fans with varied lithologies,morphologies,and sizes developed in the study area.Several factors could have influenced the development and evolution of deep-sea fans.Among them,global sea-level changes and terrestrial clastic supply had the greatest influence on the texture and size of the fan,while continental slope geomorphology determined the shape and distribution of the fan reserviors.