Campano-maastrichtian foraminiferal stratigraphy and paleoenvironment of Fika Shale, Bornu Basin, Northeastern Nigeria

Abstract

The foraminiferal stratigraphy and paleoenvironment of the Fika Shale, Bornu Basin had been studied from the Kasade-1, Kinasa-1 and Mbeji-1 wells. Foraminifera were picked from washed samples and studied under the reflected light microscope. The well sections yielded fairly abundant but less diverse assemblage of foraminifera which consisted principally of the agglutinated family Lituolidae (Ammobaculites, Haplophragmoides and Ammotium) and the planktic assemblage represented by the Heterohelicids group (Heterohelix, Pseudotextularia and Guembelitria). The absence of calcareous benthics in the studied sections of the three wells had been attributed to high anoxia resulting from increased organic matter flux to the basin. Foraminifera distribution pattern of the well sections allowed the delineation of three informal zones - Heterohelix globulosa/Pseudotextularia elegans, Heterohelix navaroensis and Ammobaculites spp. zones based on the First Appearance Datum (FAD), Last Appearance Datum (LAD) and the relative abundances of the nominate taxa. The well section had been dated Campanian to Maastrichtian based on the presence of Pseudotextularian elegans, Heterohelix globulosa and Heterohelix navaroensis. The bulk of the studied sections with Heterohelicids which were the only planktic species recorded in the study were characteristic of shallow, inner neritic epieric seas. A transitional (lagoonal and estuarine) environment had been inferred for the part of the sequences with the dominant occurrence of agglutinated benthic foraminferal species (Ammobaculites, Haplophragmoides and Ammotium) which were typical of brackish water environment.

Keywords: Foraminifera, Stratigraphy, Campanian, Maastrichtian, Fika, Paleoenvironment, Heterohelicids