Age and paleo-environmental evolution of the Douala Basin (Cameroon) during the Cenozoic: insights from palynology and sequence analysis

The Douala basin in Cameroon is one of the West African basins created during the opening of the South Atlantic Ocean after the break-up of the Gondwana superstructure. Until now, no detailed studies of age and paleo-environmental evolution of this basin during the Cenozoic have been carried out, especially on outcrops sections. Palynological and sequence analyses have been performed on the outcrops in the Missole I and Dibamba localities in the central part of this basin. This integrated approach allow us propose a new age and paleo-environmental evolution of the Douala Basin. Three palynomorph assemblages have been identified: (i) the Paleocene-Eocene palynomorph assemblage (A) from the Missole I deposits; (ii) the Oligocene palynomorph assemblage (B) from the lower part of the Dibamba deposits; and (iii) the Lower to Middle Miocene palynomorph assemblages (C) from the upper part of the Dibamba deposits. Sequence analysis indicates four depositional sequences with a vertical succession, characterized by major transgressive depositional sequences (depositional sequence “a”, “b”, and “c”), and a minor regressive depositional sequence (“d”). The trangressive sequences were deposited in lagoon or marginal marine environments during Paleocene-Eocene, while the regressive sequence was deposited in prograding continental shelf during the Oligocene-Middle Miocene. The recognized depositional sequence and associated depositional environments were controlled by spasmodic subsidence, margin uplift and climatic variations. Climate evolved from a wet-dry subtropical to tropical during the Paleocene-Eocene and a warm humid subtropical during the Oligocene up to Lower Middle Miocene with overall shift of the Douala basin from the Southern to the Northern hemisphere. This study reveals the existence of Oligocene deposits (Souellaba Formation) in the outcrops and could be useful for future correlation with the offshore part of the Douala Basin.