LAUSR

Abstract Investigations were carried out on the Tertiary sedimentary sequences from west Cameroon, namely the Mamiwater well (from 268 to 828 m), the Pungo well (from 731 to 1338 m) and the Yatou well (from 700 to 1402 m). These intervals correspond to the Souellaba Formation (SFm) of the Douala sub-basin according to the well final report produced by the National Hydrocarbons Corporation of Cameroon (NHC). The aim of this study was to characterize the lithofacies, the palynological zones, and characterize the depositional environments based on palynomorphs and palynofacies. The studied intervals are dominated by shale interbedded with limestone and siltstone; a few beds of claystone, fine to medium and coarse-grained sandstone (limited to the Pungo well) and rare marl layers are also observed. Three main palynozones were identified in each well and each zone is named. The palynological composition of the assemblages is marked by the abundance of spores and pollen grains and several stratigraphic markers in the three wells such as Cicatricosisporites dorogensis, Perigrinipollis nigericus, Proteacidites cooksonii, Zonocostites ramonae, Magnastriatites howardi, Loranthacidites nataliae, Brevicolporites molinae, Triporotetradites hookenii, Marginipollis concinnus and Adhenantheridites simplex. The dominance of the latter over dinoflagellate cysts in the Souellaba Fm indicates a high continental influence. The high percentage of angiosperms pollens grains, which are dominant in the assemblages, indicates the proximity of terrestrial sources associated with oxygenated environments. Moreover, the dominance of terrestrial palynomorphs and the relative abundance of marine palynomorphs are interpreted as indicating shallow marine environments of deposition close to terrestrial source. This marine condition is confirmed by the presence of foraminiferal test linings. The abundance of plant debris within the palynofacies indicates a climatic control on the parent vegetation and suggests the proximity to fluvial inputs. The organic matter analysis reveals type III kerogen. The relatively high number of opaque phytoclasts suggests combustion events.