关键词: 大陆裂谷, 被动陆缘, 油气成藏, 西非海岸盆地

Abstract:

Formation and development of the coastal basins in West Africa had been related with the opening and later continuous spreading of Atlantic Ocean since Mesozoic.They were continental rift and passive continental margin basins formed as a result of the break-up of Gondwana and the spreading of Atlantic Ocean.Their deve-lopments had been influenced by plate tectonic evolution and had experienced late Paleozoic-Early Mesozoic continental craton stage(pre-rift stage),rift stage and transition stage since Middle-Late Mesozoic,and passive continental margin stage by the end of Mesozoic-Tertiary.Formation of the basins was characterized by early in the south and late in the north,due to the influence of the opening of South Atlantic being early in the south and late in the north.Basins in the central part of the rifts were well developed,followed by basins in the southern part,while those in the northern part were relatively poor.A thick halite was widely developed in this area at the end of rifting.Early development of passive continental margin basins had inherited the sedimentary features in the rifting stage,but their features in late stage(post-Eocene) were contrary to that in the rifting stage,very thick Nigeria deltaic sediments had been deposited in the northern part.The formation of oil and gas reservoirs was obviously later in the northern part than that in the southern part.Petroleum systems in basins to the south of Gabon basin are mainly of those below the halite,while those in Nigeria basin are mainly of Tertiary petroleum systems developed above the halite.The formation of oil and gas reservoirs is closely related to structures formed by halite activities.The oil-and gas-bearing layers get younger toward the ocean.

Key words: continental rift, passive continental margin, hydrocarbon accumulation, coastal basins in West Africa