Provenance, sedimentation environment, tectonic setting and correlation of Plio-Pleistocene post-volcanic deposits from Adamawa region (Cameroon, Central Africa): impact of Precambrian fault reactivation during the evolution of the South Atlantic Ocean on Cenozoic rock units

Terrigenous sediments located along the Central Cameroon Shear Zone and the Cameroon Volcanic Line, respectively, in the Mbere and Laopanga basins located in the Adamawa Region, were subject to provenance, paleoenvironmental deposition, and tectonic setting studies, using palynological, mineralogical, grain shapes and facies analyses. The stratigraphic succession consists of two positive sequences and seven lithofacies (Gcm, Gmm, Sm, Sh, St, Fml, and Fh) in the Mbere Basin and five positive sequences and six lithofacies (Gcm, Gmm, Ghm, Sm, Sh, and Fml) in the Laopanga Basin, deposited in an active tectonic context. The deposits vary from proximal to sub-distal in the Mbere Basin and are mainly proximal in the Laopanga Basin. The heavy mineral analysis highlights several distributing sources, with minerals from basic volcanic rocks (olivine and basaltic hornblende), metamorphic rocks (kyanite, andalusite, and sillimanite), minerals from metamorphic and volcanic rocks (augite, diopside), and minerals common to all types of rocks (zircon, garnet, and hornblende), indicating the heterogeneous source rocks. The deposits lack any marine species, and the pollens and spores’ assemblages include Ricceaceae, Chenopodiaceae, Malvaceae, Gramineae, Compositae. The available geochronological data of volcanic rocks suggest a Plio-Pleistocene age to these sequences. Sedimentary structures and palynological data indicate a continental fluvio-lacustrine environment of deposition. The lightly abundant kaolinite and the presence of ferric minerals associated to sporopollenite species indicate a more or less hot and semi-arid climate. The Phanerozoic reactivation of Precambrian faults has led to the setting up of continental depression as in the cases of Laopanga and Mbere basins.