Biostratigraphy Studies Of Tuma-1 Well Chad Basin Nigeria

AbstractThese The upper cretaceous sediments of the Chad basins have been studied from ditch cuttings and core samples from Tuma- well. The sedimentary sequences penetrated and sampled in Tuma-1 well include the Pliocene pleistocene lacustrine sediments comprising mostly clays sandy and silty clays and sand belonging to the Chad formation and the highly distinctive upper cretaceous dark-gray silty carbonaceous shale unit which underlies it. The foraminiferal assemblages of the upper cretaceous dark gray shale unit underlying the Chad Formation is dominated by arenaceous benthonic foraminifera comprising mostly Haplophragmoides species such as H. sahariensis H. Hausa. H. Rugosa H. baucnensis H. benuensis and H. pindigensis and Ammobacultes species which include Ammobaculties Numanhinsis A. benuensis A. irregularity formis and A. numanninsis. A. benuensis. A. irregulariformis and A. bauchensis.s few specimens of calcareous benthonic speces such as lenticulina sp and Reophax sp are also associated with the assemblages. The calcareous benthonics constitute less than 1 of the entire assemblages recovered while the arenaceous assemblages makeup over 99 the sequences above the upper cretaceous unit yielded very few specimens. The generic composition of the assemblages characterized by a low diversity coupled with the presence of carbonaceous and micaceous material suggests a probable marshy estuarine lacustrine environment of deposition for the upper cretaceous shale unit. The phosphatic and gypsiferous nature of the samples and their associated foraminiferal assemblages are indicative of a shallow marshy hypersaline marine depositional environment fo the study section.