Although there is no proof of the existence of salt-beds in the Benue Trough, outcrops of saline groundwaters are common features associated with the anticlinal structures in this trough. The outcrops in the Ogoja area, referred to here as the “Ogoja brine field”, situated at the eastern margin of the Lower Benue Trough, are presented as a case study. The saline groundwaters in this brine field, which occur as ponds and in dug-wells, support an age-old local salt production in this area. The saline waters are characterised as Na-Cl type with Na+ constituting 78-85% of the cations and Cl- accounting for at least 85% of the anions. Ogoja brines display specific straight-line relationships between chloride and alkaline-earth metals, especially with lithium. Barium and strontium appear to be enriched, the former due to an environment free of sulphate. On the other hand, the observed depletion of the underground saline waters with respect to tritium (< 1.5 TU) and stable isotopes of oxygen and hydrogen (<-3.5‰ δ18O and <-10.5‰ δ2H) suggests little or no surface in-put (or near surface mixing) relative to those of the surface saline ponds (-0.15 to -3.3‰ δ18O and -6 to -10.4‰ δ2H). The combination of hydrochemical and isotope data, coupled with the analyses of the stratigraphic setting of the area suggests that the brines are marine in origin, related to palaeo/fossil sea water embedded within the transgressive marine sediments, and/or disseminated (precipitated) salts formed within the regressive interbeds during the sedimentation cycle.
Journal of African Earth Sciences 08/1996; 23(2-23):237-252. DOI:10.1016/S0899-5362(96)00065-6