Lithofacies, palynofacies, and depositional system of a mixed travertine-sinter-alluvial succession in a fault-controlled continental extensional basin (Laopanga, Adamawa Region, Cameroon)

Abstract

Lithofacies and palynofacies were investigated from deposits of the Laopanga Basin to provide sedimentation conditions and their evolution during the Cenozoic Era. Deposition occurred in an active tectonic setting giving rise to six facies including laminated, reeds/fossils-rich, bubble mat, massive, packed fragmental and botryoidal lithofacies and various microfacies (mudstone, wackestone, packstone, grainstone and floatstone). They record precipitates in the form of travertines, pure sinters and carbonate sinters interfingering with alluvial deposits (conglomerates, sandstones and claystones with silica and carbonate cements) as a result of tectonics and climate fluctuations. Sedimentation has been affected by several erosional events which affected the sedimentary basin. The precipitates suggest different temperature of deposition, ranging between 30 °C to 70 °C, likely related to lateral gradients from proximal to distal deposits. The mixing of sinters and travertines suggests a geothermal upflow and outflow and a probable migration of the spring controlled by tectonics related likely to reactivation of the Precambrian fault during the Cenozoic period. Freshwater algal and fungal remains such as Chomotriletes minor and the fern monolete spores Laevigatosporites sp. point to freshwater inflow from terrestrial habitats. Occurrence of other monolete spores such as Polypodiaceoisporites sp. indicates a similar marshy environment. Microbial communities (i.e. cyanobacteria) including coalesced silica spheres and filamentous bacteria reflect their influence on the chemical deposits, in active hydrothermal systems. The mixed precipitates and alluvial/terrigenous deposits are reported elsewhere as for example in the alluvial deposits in Namibia, Italy and Tunisia, meanwhile, the case ofinteraction between travertine-sinter-terrigenous deposits is exceptional.