Depositional Environment of Tertiary Sediments in...

Depositional Environment of Tertiary Sediments in Calabar Flank: A Case Study of Pebble Morphometric Analysis Occurring Around 25km of Calabar-Itu Road, Southeastern Nigeria

Abstract

Pebble morphormiteric analysis of some selected beds deposited around 25km of Calabar-Itu Road in Calabar Flank, Southeastern Nigeria, was carried out in order to determine the paleodepositional environment of the pebble suites. A total number of 700 unweathered quartz pebbles were collected from the study area, comprising of 50 samples respectively from 14 locations. The results of the pebble morphometric parameters included: Flatness Ratio (FR), Coefficient of Flatness Ratio (CFR), Elongation Ratio (ER), Maximum Projection Sphericity Index (MPSI) and Oblate Prolate Index (OPI), have average and range values of 0.55 (0.51 - 0.59), 55.32% (50.84 – 59.36%), 0.74 (0.70 - 0.76), 0.73 (0.70-0.77) and 1.50 (0.10-2.39) respectively. These values were inferred from those pebbles within the study area and were mostly found to have been deposited in a fluvial setting than in beach. Roundness values average 44.26% and ranges from 38.27% to 58.94% showing fluvial setting, while the various bivariate plots of the pebble parameters and forms show a mixing of both fluvial and beach/marine settings for pebbles found within the investigated area

Introduction

The study of clastic grain size analysis has proven to be a good reliable tool in inferring paleodepositional environment (Nwajide and Hoque 1982; Inyang and Enang, 2002; Inyang et al, 2014; Itam et al., 2015; Zarma et al., 2015; Itam and Ugar, 2016; Essien et al., 2017, Madi et al ;2020; Oluwajana et al.2021 and Ogbe et al.2023.) This approach had been used to carry work especially on some outcrops which are devoid or almost totally barren of paleoenvironmental fossil indicators. In highly ferruginised sand/conglomerate units, where the sand is highly weathered and cannot be used to infer the paleodepositional condition, pebbles have proven to be a better tool in deciphering the environment where the sediments were deposited. With the growing population in Cross River State of Southeastern Nigeria, different road networks are opened up for accessibility. This has led to the discovery of unknown conglomeratic beds which occurred close to a shale unit as shown in Ikot Nkpara Otop (Figure 1). There has been controversy about the depositional setting of this outcrop by many scholars in geology. The present study will attempt for the first time, to use the various pebbles exposed in Ikot Nkpara Otop around 25km of Calabar-Itu Road, in Calabar Flank Southeastern Nigeria to unravel the paleodepositional unit of this suite of sediments