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 CalabarFlank.  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, ripplemarks) 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 (ɸ1.02 –2.03). Skewness and kurtosis values range from strongly coarse -coarse skewed (ɸ-0.66 –0.13) and leptokurtic to platykurtic (ɸ0.72 –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.

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