Sedimentary Processes and Environments of Deposition of Part of the Benin Formation, Southeastern Nigeria

This chapter involves the study of the sedimentological processes and depositional environment from
two major exposed sections of the Benin Formation in the vicinity of the southern fringes of the
Calabar Flank. Stratigraphic logs were produced; textural description was carried out using 20
samples collected from the road cuts. Within the mudstone interval, lenticular beds and skolithos
traces were observed. Other sedimentary structures (cross beds, ripple marks) were measured and
analysed for paleocurrent patterns. The results from the textural analyses of the sandstones show that
the sediments were predominantly medium to coarse grain (ɸ -0.13 – 1.63), moderate to poorly sorted
(ɸ 1.02 – 2.03). Skewness and kurtosis values range from strongly coarse - coarse skewed (ɸ -0.66 –
0.13) and leptokurtic to platykurtic (ɸ 0.72 – 2.00) respectively. Bivariate analysis reveals that 100% of
the sandstone samples are continental (fluvial) in origin with predominant deposition within rolling and
saltation sub-population of the C-M plot. The points were restricted to the P-Q section of the C-M plot
signifying high energy deposition. Lenticular beds characterized tidal influence in the thick mudflat
deposit. Break in sedimentation was identified by the presence of a paleosol and the unimodal and
unidirectional pattern of the paleocurrent markers suggest fluvial setting.