INTRODUCTION

JURASSIC TIME

EARLY CRETACEOUS TIME

LATE CRETACEOUS TIME

SEA LEVEL

CONCLUSIONS

        The depositional character of the sediments changed in the South Atlantic Ocean during the Mid Cretaceous period. Mainly tectonic movement and the rate of sediments that accumulated in the basins caused this change. Some authors believe that there was a super plume episode in Mid Cretaceous time (e.g. Roger, 1995) and possible volcanic activities in the Aptian-Albian and Campanian-Masstrichian times (Schanger and Arthur, )
        Transitional oceanic crust was formed after the total separation of South America from Africa. This separation increased the accommodation of the sediments between Africa and stabilized the oceanic influence on this margin. The deposition of the sediment accumulation in the South Atlantic Ocean was in response to the rise of sea level from Albian to Turonian (Seiglie and Baker, 1980). The sediments of the same interval were deposited in a high stand system tract.

        The climate began to change in the South Atlantic Ocean during this period. Africa and South America moved a little to the south, changing their initial position relative to the Equator. The Equatorial radius began to increase slowly, moving South America far away from Africa and causing a change of  habitat of the living organisms of this time (Parish, 1990).
        The Cretaceous climate was affected by mountain building in the western part of South and North America and by super plume    episodes ( Roger, 1995). The super plume episodes were probably caused by upweling of material from one or more plumes that erupted during mid Cretaceous time (Roger, 1995). The main effects of this eruption were to cause the increase of the sea level in response to the rise of the sea floor; to change  the atmosphere with high content of carbon dioxide; and to change the Sun's radiation in response to changes in the inclination of the earth's axis (Parish, 1990)

        The formation of oceanic crust and the process of sea floor spreading took place in the Late Cretaceous. This period established the true marine setting of the study area. The succession of the sediments in the post rift interval is a complex mix of carbonate and siliciclastic sediments (Liro et al, 1995). The deposition of the sediments in this interval occurred in different system tracts responding to two major Cretaceous transgressive and regressive cycles that occurred in the West African basin (Seiglie and Baker, 1980) Marine transgressive events occurred in the Sergipe Alagoas basin at the end of the Cretaceous period. The thickness of the Oceanic crust along the Western African margin is nearly constant and is about 5.63 km (Rosendahl and Backer, 2000).

Fig. 9. Map showing the beginning formation of the oceanic crust in the South Atlantic Ocean, Cretaceous about 68 Ma