Preliminary investigation of Late Turonian-Early Campanian shallow marine foraminifera of the Mungo River/Logbadjeck Formation, NW Douala Basin, Cameroon

Sediments of the Mungo River (also Known as Logbadjeck) Formation outcrop in several small sections in areas around Bombe, Mbalangi and Ediki villages in Meme Division of the South West Region of Cameroon. Outcrops were encountered mainly along river channels notably, the Mungo, Ediki, Kendonge and their tributaries and other exposures in farmlands. All the lithofacies described elsewhere from subsurface samples are represented in this area (shales, limestones and marlstone, frequently intercalated by sandstones and siltstones). However, only a composite stratigraphic framework for the study area can be constructed from these small isolated outcrops. A fairly abundant and diverse foraminiferal assemblage was recovered from mostly the shales and marlstones and includes both the planktonic and almost exclusively calcareous benthonic forms. The heterohelix and hedbergella dominated the planktonics while others include: Whiteinella inornata, Marginotruncana renzi, Clavihedbergella subcretacea and Pseudotextularia elegans. The calcareous benthonics are represented by: Gavelinella nacatochensis, Cibicides harperi. Planulina beadnelli, and several Bolivina sp. While the benthics only generally lend support to an upper Cretaceous age for these sediments, the planktic association strongly indicates a Late Turonian-Early Campanian age for the sediments representing the middle section of the Mungo River/Logbadjeck Formation. The planktonic predominance by the heterohellids and the globigerine shaped hedbergllids offers an important paleobiogeographic significance. A generally new shallow seaway probably middle neritic depositional environment of up to about 30 m deep has been inferred. The almost exclusive calcareous benthic assemblage indicates a paleodepositional environment deeper away from marginal areas.