Litho-Bio Facies Analysis and Systematic Paleontology of Sediments in Amansiodo-1 Well, Anambra Basin, Southeastern Nigeria

Abstract

Sixty-two (62) ditch cutting samples were obtained from Amansiodo-1 well within the Anambra Basin, Nigeria, at depth intervals between 16 - 2191 m and analyzed for lithofacies, Foraminiferal, and systematically described. A total of thirty (30) benthonic foraminiferal species were retrieved: twenty-six (26) arenaceous and four (4) calcareous. The age of the well is determined to be Maastrichtian base on the appearance of benthonic arenaceous <i>Haplophragmoides saheliense (</i>Petters) species. Facies analysis of the samples indicated ten (10) lithofacies and two (2) facies associations. The facies comprise a base to top, the shale facies, shale/sandstone facies, shale/mudstone facies, mudstone/coal facies, sandstone/clay facies, mudstone/clay facies, very coarse sandstone facies, coarse sandstone facies, sandstone/clay facies and siltstone/clay facies, association FA-1 (subtidal) and FA-2 (Intertidal) corresponding to the Mamu Formation in the Anambra Basin. The studied sediments are assigned a shallow marine depositional environment based on the triangular plot of foraminiferal suborder test type (arenaceous, porcelaneous, and hyaline) and lithofacies distribution. The paleosalinity studies suggest a transition from brackish to an open marine depositional environment. Also, paleo-oxygenation of the sediments is anoxic based on foraminiferal distribution and the ratio of epifaunal to infaunal benthonic foraminifera respectively.