Abstract
The sedimentary sequences in the Mamfe Basin are generally thought of as continental (fluvio-lacustrine) in origin. But the wide spread occurrence of salt springs and salt accumulations and in places gypsum, often puts to question the exclusive continentality throughout this basin’s history. The sequences studied portray a wide range of complex lithologies and lithofacies relationships and include basal and intra-formational conglomerates, sandstones, shales, carbonaceous, carbonate and halite facies respectively. All these are well exposed at several outcrop sections distributed all over the basin with some measuring up to and above 30 m in height. Sedimentary structures include: parallel aligned imbricated prismatic pebbles, plannar to trough-cross stratifications, fining upward grain size distribution and thin frequently alternating sandstone-shale beds. Palynological data have been obtained for the first time from the shally and carbonate intervals and integrated with five lithofacies associations, permitting the determination of the ages and paleo environmental reconstruction. The palynomorphs are characterized by pteridophytic spores dominated by Cicatricosisporites sp.,Cyathidites sp. and Deltoidspora sp., pollen grains include gymnosperms dominated by Classopollis annulatus and Classopollis todosus and angiosperms represented by Retitricolpites sp. and Retimoncolpites sp., fungal remains include some hyphae and Fusiformisporites sp. Only a few dinoflagellate cysts dominantly Spiniferites were encountered at Nfaitok outcrop, suggesting a proximal sea water influence. A fluvial, lacustrine-deltaic and an anoxic deep bottom lake setting sub-environments were reconstructed with no marine strata encountered. The brines are here suggested to have originated from sea water splay over a barrier and complimented by the chemistry of the drained surrounding country rocks. The palynomorph assemblage suggests an Aptian-Turonian age for the studied sequences and a chronostratigraphic sequence in which the Nfaitok and Satom Bridge units are both Late Cenomanian-Turonian (lateral equivalents of each other) are younger and overlie the Aptian-Early-Cenomanian Okoyong sandstone unit.
Highlights
The sedimentary sequences that make up the Mamfe Basin portray a wide range of complex lithologies and lithofacies relationships which hitherto are still to be well understood and defined
Age Determination Very little has been published on the palynology of sedimentary basins in Cameroon and the present analysis is based by comparing with palynolostratigraphy of the basins in Nigeria, Ghana, Cote d’Ivoire, Senegal, Egypt, Libya and Angola in Africa and several genetically linked basins along the east coast of South America
Palynomorphs from Cretaceous sedimentary sequences in the Mamfe Basin have for the first time been recovered and used in determining the ages of some exposed strata
Summary
The sedimentary sequences that make up the Mamfe Basin portray a wide range of complex lithologies and lithofacies relationships which hitherto are still to be well understood and defined. The major facies that are frequently encountered include basal and intra-formational conglomerates, sandstone, shale, carbonaceous, and carbonate facies respectively All these are well exposed at several outcrop sections distributed all over the basin with some measuring up to and above 30 m in height. Previous authors have worked on various geologic aspects of this basin such as the initiation of the framework of the geological map of the basin [1]-[4]; gravity survey [5]-[8]; audiomagnetotellurics [9]-[11]; aeromagnetic survey [12] [13]; lithostratigraphy [14]-[18]; geochemistry [19]; and general geology [20] [21] Most of these authors have reported the wide spread occurrences of salts and salt springs and carbonates while [20] reported these and gypsum from the Nfaitok unit
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