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Abstrakt

Pebble morphometric investigations on pebbles belonging to the Benin formation at NSIE and environs, Southeastern Nigeria

Bassey E. Ephraim, Chukwuka Amaechina and Chukwuemeka F. R. Odumodu

Pebbles samples collected from a burrow pit located along Eket – Oron expressway in Nsie and environs of southeastern Nigeria were subjected to pebble morphometric analysis in order to diagnose the environment of formation. Results indicate predominance of fluvial processes, with flatness ratio (FR) = 0.54 ± 0.13, elongation ratio (ER) = 0.73 ± 0.14, maximum projection sphericity index (M.P.S.I) of 0.73 ± 0.09 (fluviatile) and oblateprolate index of 1.3 ± 5.4 (fluvial). Also, compact (C), compact bladed (CB), compact elongate (CE) and elongate (E) pebble forms which are common within the study area supplied additional strand of evidence in support of fluvial setting. In Addition, plots of roundness versus elongation for the pebbles shows 16% of the pebbles in the littoral field, 6% in the transitional field and 24% in the fluviatile field. Furthermore, bivariate plot of flatness ratio (FR) versus maximum projection sphericity index (M.P.S.I) shows majority of the pebbles falling within the fluvial field, and scatter plot of sphericity versus O.P index shows 75% of the pebbles from Nsie and environs occurring within the river environment and 25% within the beach part of the plot. All these features indicate deposition under fluvial regime. Thus, the study shows that the Benin Formation formed as a result of mostly fluvial depositional processes.