Abstract
Ditch cutting samples from Kasade-1 well were processed for microfauna, nannofossil and palynomorphs to throw more light on biostratigraphic events in the northern portion of the Bornu Basin, Nigeria. The lower section of the well within interval 990 - 1565 m yielded fairly abundant foraminifera species, while the upper section was barren. Palynomorph distribution follows the same pattern as observed for foraminifera except that few fresh-water algal species, Botryococcus braunii, were recovered from the upper section. The samples are devoid of nannofossil but contain few ostracod species, echinoid remains and fish tooth. Recognition of two planktonic foraminifera zones, Globotruncanella havanensis and Globotruncana aegyptiaca, enabled the delineation of the Campano-Maastrichtian and Maastrichtian boundary. The Cretaceous Tertiary boundary was inferred based on the top occurrence of palynomorph Dinogymnium euclaense. An abrupt truncation in the distribution of foraminifera species at a depth of about 990 m suggests unconformity, a widely reported event that followed the Santonian squeeze in the entire mega-Chad Basin.
Highlights
The renewed search for hydrocarbon in the Bornu Basin, Nigeria (Figure 1), makes the understanding of biostratigraphic events in the basin of paramount interest
Micropalaeontology The two hundred and eighty six ditch cutting samples retrieved within interval of 60 - 1565 m of Kasade-1 well were composited to forty three and processed for foraminifera and accessory microfauna
Microfauna From the forty-three (43) composited ditch cutting samples taken within the interval of 60 - 1565 m of Kasade1 well and processed for foraminifera and accessory microfauna, only fifteen (15) foraminifera species were recovered
Summary
The renewed search for hydrocarbon in the Bornu Basin, Nigeria (Figure 1), makes the understanding of biostratigraphic events in the basin of paramount interest. Studies of the dinoflagellate cysts of the deepest well, Kinasar-1, in the basin reveals that the well bottomed within the Cenomanian sediments [2]. Earlier study of the sequences penetrated by the well using ostracod reveals age of Albian at a depth of about 1750 m [3]. The age of the fossiliferous interval of Kemar-1 as studied by [4] shows early Turonian at the base. According to [5], the Fika and Gongila Formations contain Turonian to Santonian ostracods but lack palaeontological evidence for marine Santonian to Campanian sediments. Paleoenvironment within this intercontinental basin ranges from fluviomarine through coastal deltaic to shallow marine/open marine. Details of the lithostratigraphic succession in the basin are contained in [6] [7]
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