Foraminiferal biostratigraphy and paleoenvironmental study of the sediments penetrated within the interval of 6030ft. to 11115ft. of ash-3 well in the greater Ughelli Depobelt, Niger Delta Basin

Abstract

Foraminifera biostratigraphy and paleoenvironmental study was carried out on sediments penetrated by Ash-3 Well in the Greater Ughelli Depobelt, Niger Delta. The aim of this study is to erect a foraminifera zonation and carry out paleoenvironmental study of Ash-3 Well. Seventy (70) ditch cutting samples were subjected to foraminifera slide preparation technique and analysis was carried out with reflected light binocular microscope. Most of the species recorded are calcareous and arenaceous (agglutinated) benthic foraminifera species with planktic generally absent in the well. Four (4) foraminifera genera and twenty six (26) foraminifera species were recovered from the well. Two benthic foraminefera zones were identified: Lower N2- N4 and N4 – N5 Zones of Blow (1969, 1979). The age of the well from 9960ft – 11115ft indicates an Oligocene age based on the recovery of age diagnostic markers such as Spirosplectammina wrightii, Altistoma scalaris, Hopkinsinna bononiensis, Haplophragmoides narivaensis, Spirosigmoilina oligocaenica, Eponides eshira, Lenticulina grandis and Poritextularia panamensis, while the age from depth 6030 ft. - 9945ft. indicates Early Miocene age based on the recovery of age diagnostic markers such as Lenticulina grandis, Florilus costiferum, Lenticulina inornata, Eponides eshira and Poritextularia panamensis. Paleoenvironmental study based on the benthic foraminifera association revealed that the sedimentary sequences were deposited in range of environment from marginal marine environment (littoral Zone) to shallow marine environment (inner neritic zone). The alpha diversity index for Ash-3 Well based on the plot of the amount of benthonic foraminifera species against the number of individual foraminifera ranges from α2 – α5, this therefore indicates that the salinity during the deposition of the sediments of Ash-3 Well was within the hyposaline marshes – hyposaline shelf sea, which implies that the salinity of the water condition during this time was abnormally low salinity.

Keywords: calcareous, arenaceous, agglutinated, hyposaline marshes, hyposaline shelf sea.