TITLE:
Aptian-Late Cenomanian Fluvio-Lacustrine Lithofacies and Palynomorphs from Mamfe Basin, Southwest Cameroon, West Africa
AUTHORS:
Olivier A. Njoh, Miriam B. Nforsi, Junie N. Datcheu
KEYWORDS:
Cretaceous, Lacustrine, Lithofacies, Mamfe Basin, Palynomorphs
JOURNAL NAME:
International Journal of Geosciences,
Vol.6 No.7,
July
30,
2015
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 byCicatricosisporitessp.,Cyathiditessp. andDeltoidsporasp., pollen grains include
gymnosperms dominated byClassopollis
annulatusandClassopollis todosusand angiosperms represented byRetitricolpitessp. andRetimoncolpitessp., fungal remains include some
hyphae andFusiformisporitessp. Only a few dinoflagellate
cysts dominantlySpiniferiteswere 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.