ABSTRACT
One hundred and fifty (150) ditch cutting samples from NAS- 1 Well, Gongola Basin, Northern Benue Trough, collected from Research and Development Division of Nigerian National Petroleum Cooperation were subjected to lithological and foraminiferal analysis with the aim of zoning, age determination and interpretation of palaeoenvironment of the analyzed section of the well.
Lithological analysis was carried out between 990ft and 6240ft at 30ft sampling intervals. Various lithofacies, together with their associated mineral units were observed mainly by visual examination, taking note of the color, grain sizes, shape and sorting patterns of the samples provided. Result of lithological analysis yielded four (4) lithofacies which includes shale, shaly sand, sandy shale and sandstone and as a result, fourteen (14) lithozones were established. Nine (9) ditch cutting samples taken across the well between I 500fl and 51 90ft were subjected to standard methods and techniques employed in the research institute and oil industry for foramini feral analysis.
A total of forty-three (43) foraminifera species were identified, with the agglutinated benthics making the larger percentage and very few planktic foraminiferal species. Five (5) informal benthic foraminiferal zones- Haplophragmoides hausa zone, Haplophragmoides ha, (chens Ls’ zone, A mm oscalaris pseudospir ills zone, Ammobaculites sp zone and Haplophragmoides sp zone were delineated. A Turonian — early Maastrichtian age (Late Cretaceous Epoch) was assigned to the analyzed interval ( I 500ft-5 1 90ft). Due to the occurrence of benthic foraminiferal species- Haplophragmoides pindigaens is, Haplophragmoides bauchens is and Ammobacuiites coprolithifbrmfs, which are characteristic species of Turonian to early Maastrichtian age, \vnich corresponds with the works of previous authors. Turonian to Coniacian age was assigned to the interval between 5 90ft and 3300ft, Campanian/early Maastrichtian age to interval 3300ft-2600ft and finally an early Maastrichtian age to interval 2600ft-l500ft. Based on the recovered benthic foraminiferal association t was revealed that the analyzed interval (1500fl - 5190fi) was deposited in a Transitional to Inner Neritic, slightly low salinity environment.