Paleogeographic Evolution of the Eastern Edge of the Douala Basin from Early Cenomanian to Turonian

ABSTRACT

In order to trace the paleogeographic evolution of the eastern edge of the Douala basin from lower Cenomanian to Turonian, sedimentological and palynostratigraphic analyses have been carried out. The studied formations are about 80 m thick and are made up of continental detrital facies, which are coarse at the bottom and progressively become finer towards the top of the sequence. These rocks are overlain by marine deposits, composed of thin layers of black clay and bioclastic limestone. These formations were deposited during two sedimentation phases, namely, the continental deposit phase, which is composed of conglomerates infilling the basin, followed by the transgressive deposits associated with deepening of the basin environment. Sequence analysis of these different facies, indicates that the turbidites are composed of small sequences that constitute a transgressive megastructure. This succession was deposited during a megatransgressive phase that continued until the final stage of the basin infilling. According to palynologic data, strata were deposits from the early Cenomanian at the bottom to the Turonian towards the top. The depositional environment changed over time, passing from (1) a narrow and steep-sided tectonic basin, during the early to middle Cenomanian, followed by (2) a lacustrine to palustrine basin with marine incursions, as a result of the E-W distensive movements between the South American and Northwest African blocks in the middle and late Cenomanian, and (3) to a confined and shallow sea during the Turonian. The climate remained warm and became progressively humid towards the end of the Cretaceous. The nature of these environments is related to the dynamics of the opening of the South Atlantic Ocean.

Keywords:

Cenomanian, depositional environment, douala basin, paleogeography, palynostratigraphy, transgressive megasequence, turonian.