Lithofacies, Granulometric and Pebble Morphometric Studies: Outcome of Geologic Mapping of Enugwu-Agidi Area and Its Environs, Southeast Nigeria

• Author(s): Offiaukwu Kenneth Chinonso
• Paper ID: 1703462
• Page: 131-145
• Published Date: 24-05-2022
• Published In: Iconic Research And Engineering Journals
• Publisher: IRE Journals
• e-ISSN: 2456-8880
• Volume/Issue: Volume 5 Issue 11 May-2022

Abstract

This paper presents findings from the geologic mapping of Enugwu-Agidi and its environs. The Early to Middle Paleogene sedimentary succession in Enugwu-Agidi and its environs of Southeastern Nigeria comprises shales of the Imo Formation at the northern portion and the Nanka Formation at the southern portion of the study area which outcrops within the Niger Delta Basin. The aim of the work was to better understand the distribution of lithofacies, identification of various sedimentation processes from their deposits, characteristics of rock units, transport mechanisms and also to establish the Paleo-depositional environments of outcropping units by carrying out detailed geologic mapping of the study area. Based on the field mapping on 12 outcrops and Laboratory analyses which comprised granulometric and pebble morphometry studies on samples collected from the outcrops, the occurrence of 9 lithofacies, which were interpreted to infer deposits of fluvial through marine environments was observed. Paleo-current analysis was also carried out on cross beds of the rocks. The results from granulometric analyses indicate that the sandstones are fine to coarse grained, with mean size that ranges between 0.48 and 2.54. The estimated values for sorting of the grains ranges between 0.86 and 1.14, indicating that the sandstones are moderately to poorly sorted. The probability-log plots show three-segment curve types corresponding to traction, saltation and suspension which may suggest shallow marine environment and two-segment curve types corresponding to traction and saltation which are dominant, relating to deposition in fluvial environment. Studies based on the bivariate and multivariate sieve parameters show a fluvial to shallow marine environment. The three axes: the long (L), the intermediate (I) and the short (S) were measured for 100 pebbles collected from Agwu-Eke and Independent Pebble form indices such as Maximum Projection Sphericity (MPS), Coefficient of flatness (FR %), Elongation ratio (ER) and Oblate-prolate index (OPI) were calculated from these measurements with values of 0.715, 0.102, 52.29 and 0.552 respectively. Based on results from pebble morphometric analysis, the bivariate plots of MPS against OPI and FI against MPS, indicates that the pebbles have been reworked by mainly fluvial processes. The form indices diagram plot indicates that the pebbles are Bladed, Compact Bladed and platy which is diagnostic of river action. The direction of the paleo-current in the study area is NE-SW and based on palaeocurrent patterns classification, the unimodal local current vector pattern indicates fluvial, braided or meandering depositional environment.

Keywords

Geomorphological features 3, Granulometric analysis 4, Lithostratigraphic Units 2, Stacking Pattern 2, Tidal flat 3.

Citations

IRE Journals:
Offiaukwu Kenneth Chinonso "Lithofacies, Granulometric and Pebble Morphometric Studies: Outcome of Geologic Mapping of Enugwu-Agidi Area and Its Environs, Southeast Nigeria" Iconic Research And Engineering Journals Volume 5 Issue 11 2022 Page 131-145

IEEE:
Offiaukwu Kenneth Chinonso "Lithofacies, Granulometric and Pebble Morphometric Studies: Outcome of Geologic Mapping of Enugwu-Agidi Area and Its Environs, Southeast Nigeria" Iconic Research And Engineering Journals, 5(11)