Foraminiferal biostratigraphy and paleoenvironmental analyses of sediments from Folu-1 borehole, Ibeju-Lekki, Lagos State, Nigeria

Abstract

Biostratigraphic and paleoenvironmental analyses were carried out on thirty-five ditch cutting samples from interval 0.05 – 25.50 m in Folu-1 borehole, Ibeju-Lekki  Local Government Area, Lagos State. The sedimentological description of the samples revealed two (2) sequences – a lower predominantly fine to medium-grained  sandy sequence with a sandwiched sandy clay/mudstone unit and an upper fine to coarse grained, poorly sorted sandy sequence. The occurrence of abundant and  diverse planktic foraminfera permited the recognition of the N23 planktic zone and the assignment of Holocene (Milazzian) age to the studied section of the  borehole. Sequence stratigraphic studies revealed a transgressive system tract (TST) at the lowermost 25.50 – 17.25 m section and a highstand system tract (HST) between 17.25 – 9.00 m. Maximum transgression was noticed at 17.25 m depth with the maximum clay/mudstone development and the depth of highest   abundance and diversity of foraminifera. The abrupt shallowing noticed at 9.00 m depth from middle/outer  neritic environment to fluvial deposition, interpreted as indicative of an unconformity, marked the sequence boundary (SB). The identification of the unconformity and the clay/mudstone unit in the borehole section  provided an invaluable information for consideration in the construction and building purposes of which aim the hole was drilled.

Keywords: Biostratigraphy, Paleoenvironment, Unconformity, Sand, Clay/mudstone, Construction.