Abstract:
The sediments of the sequences commonly exploited for ground water and tested for foundation
purposes along the coast line of Lagos were subjected to sedimentological studies using litholog
data of cuttings retrieve during drilling and few wire line log of boreholes along the coast. The
study was designed to correlate, based on lithic characteristic, the strata of these shallow beds
classified stratigraphically as Coastal Plain Sand/ Alluvium Deposits with a view to reviewing its
stratigraphic nomenclature. To achieve uniformity, the log data containing the sedimentology
descriptions obtained from different companies were recalibrated but ensured that each facies
encountered in each depth are retained to avoid confusion where granulometric data of the cutting
are provided. They were statistically studied to know the mean, standard deviation, skewness,
Ogive, histogram and kurtosis of the sediments with a view to describing the provenance and
environment of deposition of each of the beds. Results show that based on this current work, the
beds are not correlatable, which led to the subdivision of the coastline into three major environment
of deposition: the tidal flat area (Badagry, Apapa and Ajegunle), an island within the lagoon (Ikoyi)
and the peninsular (Victorial Island and lekki). Inspite of this correlation within the subenvironment
is still poor. The Tidal flat area reflects a typical regressive sequence with fresh water
sand occurring at shallow depth when compared with the peninsular and Ikoyi areas. Peat
occurrence and prevalence of mud and mud sand typical of tidal flat are observed. Common white
sand though at deeper depth in the peninsular is characteristic of beach sand. Brownish sand at
shallow depth can be interpreted to reflect source rock and it can also be as a result of lateralization.
Characteristically, the sub-surface sediments of the coast line of Lagos down to a relative depth of
about 200 m consist of the following lithofacies: clay, peat, brownish sand, white sand with rare
sandstone that shift laterally within short distance apart. A bivariate plot (moment skewness vs.
moment standard deviation) shows the sands are fluvial in origin.
