(APTIAN-ALBIAN INTERVAL)
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SEA LEVEL
The spread of the Cretaceous sequences to the interior of the continents in the Equatorial margin of the South Atlantic Ocean is an important key to know the duration of the marine transgression in this margin. The transgression persisted through the Cretaceous time in the South Atlantic Ocean. The Cretaceous successions are well identified by most major sequence boundaries, especially in the Aptian-Santonian interval (Blick, 1990). These sequence boundaries probably were formed in response to the continuous minor variation of the sea level at a sort period time (Fig. 12).
Fig. 12. Effective source rocks and sea level curves
The study of the sea level changes between Zaire and Cameroon shows two major cycles during the Cretaceous time (Seiglie and Baker, 1980). These two major cycles are separated by two unconformities of Turonian age. Each major cycle of sea level change in the study area is divided into three minor cycles, which probably are related to the depositional rate of the sediments or the tectonic movements that happened at a very short time, whereas the major cycles correspond to the change of the sea level at a long period. The Cretaceous time ended with an important drop of the sea level in the world. This change of sea level established the boundary between Cretaceous and Tertiary sediments (Blick, 1990), which appears in many West African's basins such as Namibia, North Angola, and Equatorial Guinea (Lawrence, 1999). The sediments that overlying the Maastrichtian sequence were deposited at a lwostand system tract.
Fig. 13. Sea level curves in West Africa (Seiglie and World Baker, 1980)
VERTICAL RELATIONSHIP BETWEEN SERGIPE-ALAGOAS, DOUALA, RIO MUNI, AND GABON SEDIMENTARY BASINS
Comparative stratigraphy Sergipe-Alagoas, Douala, Rio Muni, and Gabon basins
