Septarias in the Babouri-Figuil Basin (Northern Cameroon): Morphology and controls on emplacement.

The Babouri-Figuil Basin is located in the northern part of Cameroon and is part of the Bénoué trough. One of the most remarkable features of this basin is the presence of carbonate concretions commonly called septaria. However, the understanding of nature of these concretions remains limited. In the first phase of this study a detailed field work was carried in the basin. The Babouri-Figuil Basin has four lithofacies encompassing limestones, marlstones, sandstones and conglomerates. Its depositional environment is fluvial to fluviolacustrine. These facies are organized in asymmetrical synclines and crossed by basaltic intrusions. The concretions identified occurs in the marly facies. Numerous descriptive criteria noted in the field made it possible to give their size, their context of establishment, as well as the factors which control the forms of these septarias. These septarias are greyish or dark brown and massive in structure. Their size varies from 15-57.5 cm with circumferences ranging from 23-87cm. They also have intersection cracks due to their maturity or aging. These intersection of septarian cracks are filled and indicate different generations. Ovoid, rounded, disc, elongated and chocolate bar morphologies have been observed in the study area. These shapes are controlled by the thickness and shape of the marls. Thus, where the thickness is important, the septarias are well developed and generally take ovoid, rounded or spherical shapes because the marl has weak planes. On the other hand, when the thickness of the marl is thin or in lens, the septarias tends to follow only the space and the shape that the marl occupies and, tending to make it disappear, thus creating elongated, flattened and even rounded shapes. Consequently, the septarias of the Babouri-Figuil Basin is post-sedimentary to the marl deposits.