Abstract

The Ngwa sedimentary sequence is situated on the southern flank of the Bambouto volcano. Analysis of petrography, lithostratigraphy, mineralogy, morphology and morphometry enabled the reconstruction and interpretation of their stratigraphic architecture, depositional and paleogeographic setting, the origin of the sediments and the geological history of this region. The lithostratigraphic sequence of the Ngwa sedimentary deposits reveals two major phases of sedimentation: (i) Conglomerates with pelitic sandstone matrix, pelitic sandstone and carbonaceous clayey shale with lignite intercalations; and (ii) conglomerates and arkosic sandstones. Pebbles from the Ngwa conglomerates are sub-rounded to spherical. The grain size distribution of the sandstones indicates a high amount of very fine clay particles. The sediments of Ngwa are well sorted. The homometrical character of sandstones is related to their fluvial origin. The presence of sillimanite and kyanite testifies to the metamorphic provenance of a part of the Ngwa sediments while the basaltic pebbles indicate the volcanic origin of the other part. During the Miocene, Ngwa area experienced detrital sedimentation with alternation of volcanic phases related to volcanic activity at Mount Bambouto.

Key words: Ngwa, Cameroon, lithofacies, detrital sedimentation, Miocene.