Sedimentary Processes and Depositional Environments of Part of the Benin Formation in the Calabar Flank, Southeastern Nigeria

Abstract

This research work 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; 20 samples collected from the sandstone intervals and subjected to sieve analysis. 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), moderately 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 reveal that 100% of the sandstone samples are 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.