Palaeodepositional environment of Upper Jurassic–Lower Cretaceous sediments of the Senegalo-Mauritanian Basin: Indications from facies analysis and inorganic geochemistry

Previous research on the Upper Jurassic–Lower Cretaceous sediments of the Senegalo-Mauritanian Basin has largely emphasised geophysical and organic geochemical methods, leaving a gap in understanding how depositional environments influence their hydrocarbon generation potential. To fill this gap, facies analysis and inorganic geochemistry were conducted to infer the paleodepositional environments. Core descriptions, observations and analyses identified two main facies: carbonates and siliciclastics. A dominance of carbonate, fine-grained sandstone and shale characterised the Jurassic to Aptian sequence. Albian sediments consist of limestone, shale and coarse-grained sandstone. Limestone petrography indicated a matrix-supported sediment classified as oolitic micrites, wackestones and packestones. The mineral composition of the limestones includes calcite (62%), dolomite (15%), plagioclase (14%), quartz (5%) and pyrite (3%). Dolostones are made up of dolomite (43%), calcite (22%), plagioclase (13%) and quartz (7%). The sandstone analysis revealed quartz content ranging from 51% to 60%, feldspar between 7% and 15%, and lithic fragments between 3% and 10%. The major oxides used to determine sediment provenance suggest a felsic to intermediate source for siliciclastics and marine precipitation for carbonates. Paleoclimatic proxies such as the Sr/Cu ratio indicate deposition under warm, arid climatic conditions. Paleo-salinity and paleo-bathymetry tracers suggest that, from the Upper Jurassic to the Aptian, sedimentation occurred in a shallow marine environment with normal salinity. Conversely, the Albian period was characterised by a transitional environment, marked by deposition under brackish water conditions. The findings of this study are valuable for future exploration efforts, as they will enhance the understanding of the petroleum systems.