Granulometric and Sedimentologic Study of the Sandstone Facies of the Nsukka and Imo Formations in Parts of the Anambra Basin Southeastern Nigeria

Document Type : Original Research Article

Authors

1 Department of Geology, Federal University of Technology Owerri, Ihiagwa Owerri, Imo State Nigeria, PMB 1526

2 Department of Geological Sciences, Nnamdi Azikiwe University, Awka, Nigeria

3 Department of Geology, Ebonyi State University, Abakaliki, Nigeria

4 Department of Geology, Federal University of Technology, Owerri, Imo State, Nigeria

Abstract

This study aims to investigate the granulometric and sedimentologic characteristics of the sandstone facies of the Nsukka and Imo Formations to infer their depositional environments. 35 fresh sandstone sediment samples were randomly collected from outcrops in the study area. Sieve analysis of the samples revealed three types of cumulative frequency plots identified as Type-I, II, and III. Type I distribution comprises the bottom traction or creep population, Type II saltation population, and Type III suspension population. The traction population is poorly developed and commonly constitutes less than 10%. The saltation population is well-developed, and its percentage ranges from 70 to 80%. The study showed that samples from the sandstone of the Nsukka Formation are fine to coarse-grained with a dominance of medium-grained sands (0.5-2.27ɸ, mean 1.2±0.42). The values recorded for the kurtosis showed that they are platykurtic to very leptokurtic (0.8-1.8 mean1.1±0.26). They are also well sorted to poorly sorted with a standard deviation value of 0.4-1.6 (mean 0.98±0.33) and nearly symmetrical to fine skewed (-0.01 to 0.26 mean -0.06±0.18). The overall grain size for Imo Formation sandstone shows that they are very fine to coarse-grained with values ranging from 0.07-1.07 (mean 0.69±0.33ɸ), well to poorly sorted with values ranging from 0.48-1.5 (mean 0.89±0.36), and fine skewed with values ranging from 0.17-0.5 (mean 0.33±0.13). The mean grain size of the sediments implies a high-energy-level environment of deposition with intermittent slack in depositional energy. Generally, there is a strong dominance of fluvial origin on the sediments. Results of the multivariate plots show that for the Nsukka Formation, > 90 % and >60% were deposited in a beach/shallow marine environment.

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References

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