Abstract:
This study presents the mineralogical, textural characteristics, microfossil content and
sequence stratigraphic information of the Ajali and Maastrichtian Mamu Formations, situated at
Okpekpe, western flank of Anambra Basin, Southern Nigeria. The intent is to establish their
environment and age of deposition. The investigative approach involved field studies and
collection of samples from three (3) different outcrop locations, followed by laboratory studies
which include; thin section petrography grain-size analysis (GSA), X-Ray Diffraction analysis and
plynological analysis. Detail property examination showed that Mamu Formation is characterized
by siltstone, sandstone (fine - coarse), clay, shale and heterolithic bed, while the Ajali Sandstone
consists mainly of sandstone. Texturally, Ajali Formation is a medium to coarse grained, poorly
to moderately sorted, and varied in colour from white to pinkish-brownish, negatively skewed,
leptokurtic to platykurtic. Field observation, textural plot and bivariate parameters, skewness vs
standard deviation, indicate fluvial environment of deposition. X-Ray Diffraction analysis of the
clay mineral content of the shale samples from Mamu Formation, suggests continental through
deltaic environment evidenced from the dominance of kaolinite, moderate illite and mix-layer clay
minerals. A brackish to fresh water environment is suggested for Mamu Formation, based on the
important environmentally significant species of microfossil encountered. Using palynological
evidence, Late Campanian-Middle Maastrichtian age was assigned to Mamu Formation on the
basis of some age-diagnostic palynomorph such as Longapertites marginatus, Cingulatisporites
ornatus, Buttinia andreevi and Retidiporites magdalenensis, Rugulatisporites caperatus and
Gleicheniidites senonicus. Sequence stratigraphic elements identified in the outcrop include
Lowstand and Transgressivestand and Highstand Systems Tracts
