Sedimentology and Geochemical Characteristics of Upper Cretaceous Sediments of Imo Formation Around Arimogija Okeluse, Southwestern Nigeria
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Date
2014
Journal Title
Journal ISSN
Volume Title
Publisher
International Journal of Research (IJR)
Abstract
Sediments of the Paleocene Imo
Formation exposed at the southwestern
flank of Anambra Basin at Sobe,
Arimogija and Okeluse area,
southwestern Nigeria. The sediments
consisting limestones, sandstones and
minor claystones and shales and
intercalated ironstones were studied
based on sedimentological and
petrological charateristics for
paleoenvironmental deduction. Field
observation indicated that all the beds
constituting this exposure are laminated
and exhibit a coarsening upward
succession.
The statistical result from the grain size
analysis of the siliclastic sediments
shows the sandstones are coarse to
medium sands (0.20 to 1.50ɸ), very well
to moderatelywell sorted (0.26 to 1.12 ɸ)
with skewness value ranges from nearly
symmetrical though very positively
skewed to positively skewed (-0.07 to
0.91) characterized by platykurtic to
extremely leptokurtic (0.76 to 6.83)
particle size distributions. Petrographic
study of these sandstone reveal that its
constituents is averagely of angular to
sub-angular quartz (85%), feldspar (1.4
%), rock fragment and (9.5 %) and ≤ 3%
cementing iron-oxide (goethite and
haematite) phases, texturally immature
and sub-arkosic.
The limestone comprises of bioclastic
wackestone, bioclastic wackestonepackstone,
dolomitised bioclasticwackestone
and mudstones microfacies
with the bioclasts being broken shells of
pelecypods, brachiopods and algae much
of which have been partly recrystallised
to sparry calcites. Geochemical and
mineralogical constituents also show
that the limestones are shallow marine
deposits that have variably suffered early
to mid diagenesis including
dolomitisation. The prevailing basin
condition was highly fluctuating with
diverse fluvial channel and relativelyprotected
shallow marine depoenvironments.