Structural evolution and sequence formation offshore South Gabon during the tertiary

The present investigation of the Tertiary succession offshore South Gabon is based on seismic surveys of 1985-1989 vintage and wells covering the southern part of Gabonese waters. In general, the Tertiary basin off South Gabon evolved during two structural stages. During the Paleocene and Early-Middle Eocene, a trough-like basin subsided slowly towards the west. During this period there was a cyclic development of the succession which consists of up to four sequences mostly bounded by Type 2 sequence boundaries. The sequential changes were induced by eustatic sea-level changes. This pattern changed during the Neogene when the evolution was characterized by continental crustal flexuring in Early-Middle Miocene times. This resulted in strong subsidence of the western part of the basin and uplift of the eastern part. Consequently, the eastern part was exposed to strong erosion and a thick Middle Miocene succession was deposited west of the shelf (approximately the present-day shelf), especially on the slope. The clinoformal and lens-shaped Middle-Late Miocene succession which consists of four sequences bounded by Type 1 sequence boundaries has been controlled by eustatic changes in sea level. In addition to the overall subsidence pattern, salt tectonics has modified the external and internal architecture of the sequences on a local scale. Canyon formation in connection with slumping results in the establishment of well developed fan systems on the lower part of the slope and on the basin floor area.