The Cretaceous of the Cameroon Atlantic Basin (Central Africa): sediment provenance, correlation, paleoenvironment and paleogeographic evolution of the Eastern Proto-Atlantic margin (Central Gondwana)

An integration of geochemistry, mineralogical and palynological data is used to depict the sediment provenance and distribution, the sedimentary environment and the paleogeographic evolution of the Cretaceous Atlantic Basin of Cameroon. The basin is located along the African western coast, in the heart of the Guinea Gulf, and includes the Campo, Douala, and Rio-del-Rey sub-basins from South to North. The sediments of the Campo sub-basin are derived from rocks of intermediate composition, those of the Douala sub-basin from intermediate to mafic rocks in the southern and felsic rocks in the northern parts, and those of the Rio-del-Rey sub-basin from felsic rocks with a contribution of rocks of intermediate composition. The paleoweathering index and Index of Chemical Variability values for Campo, Douala and Rio-del-Rey sub-basins range from 71.26 to 76.88 and 0.98 to 2.12, 67.15 to 99.39 and 0.37 to 0.90, and 73.17 to 92.90 and 0.44 to 10.03, respectively, indicating sub-maturity, high maturity and sub- to high maturity deposits. Al2O3 vs. V and Al2O3 vs. P2O5 plots, and palynologic data such as marine (e.g. dinoflagellates and microforaminifera) and continental (e.g. Classopollis sp., Ephedripites sp., Botryococcus sp.) species suggest a deposition in more or less deep lacustrine (Campo sub-basin), fluvio-deltaic to shallow marine (Douala sub-basin), and marginal to shallow marine (Rio-del-Rey sub-basin) environments. The paleoweathering index values, the clay minerals (kaolinite, illite and chlorite/vermiculite) distributions, and the palynological data point to arid to semi-arid climate in the Campo sub-basin and semi-arid to periodically humid conditions in the Douala and Rio-del-Rey sub-basins. The tectonic setting diagram suggests collision tectonic events that are inconsistent with the classic geological history of the Atlantic Basin. The situation is in fact related to Precambrian events that affected the basement rocks from which the studied sediments were derived, and probably to the compressional tectonics during the evolution of the South Atlantic Ocean. Although these sub-basins share the same geological history, there are some differences, such as the degree of sediment maturity, the diagenetic effects, the lithology of rock sources, the paleoenvironments of deposition and their fluctuation, depending on the moment the tectonic of Atlantic opening reached them (northward progression of the W-E extension) and the northern shearing along the southern area of the Benue through axis (Rio-del-Rey). The geological history of the Cameroon Atlantic Basin is similar to those of Gabonese and Nigerian basins, along the African western coast, and of those of the Brazilian basins along the eastern coast (Santos Basin to Pernambuco-Paraiba Basin).