Granulometric and pebble morphometric applications to Benin Flank sediments in western Anambra Basin, Nigeria: proxies for paleoenvironmental reconstruction

Abstract

Integrated granulometric and pebble morphometric study of Late Cretaceous rocks of the Benin Flank, Nigeria, were used to delineate depositional process and environment of the rocks in the study area. Granulometric analysis reveals that the sandstones of the Lokoja Bassange Formation have an average graphic mean (Mz) of 0.59Φ (coarse grains), inclusive graphic standard deviation (δi) of 1.36Φ (poorly sorted), graphic kurtosis (Ka) of 1.12Φ (leptokurtic), and inclusive graphic skewness (Ski) of - 0.14Φ (stongly coarse skewed). The sandstones for the Mamu Formation have an average Mz of 1.42Φ (medium grains), inclusive graphic standard deviation (δi) of 0.74Φ (moderately sorted), graphic kurtosis (Ka) of 1.43Φ (leptokurtic), and inclusive graphic skewness (Ski) of 0.02Φ (nearly symetrical). The sandstones for the Ajali Formation have an average Mz of 1.23Φ (medium grains), inclusive graphic standard deviation (δi) of 1.21Φ (poorly sorted), graphic kurtosis (Ka) of 1.46Φ (leptokurtic), and inclusive graphic skewness (Ski) of - 0.17Φ (nearly symetrical). Pebble morphometric analysis of the larger grains reveals that the mean values of elongation ratio (ER) = 0.69, coefficient of flatness (FI) = 54.90%, oblate-prolate index (OPI) = 3.34, the maximum projection sphericity index (MPSI) = 0.75, form = 0.67, and roundness (ρ) = 36.28% for the Lokoja Bassange Formation; ER = 0.76, FI = 37.07%, OPI = -3.20, the MPSI = 0.53, form = 0.38, and ρ = 52.93% for the Mamu Formation; and ER = 0.72, FI = 47.44%, OPI = 1.12, the MPSI = 0.67, form = 0.54 and ρ = 42.68% for the Ajali Formation. The integration of the various granulometric and pebble morphometric data, different bivariate and ternary plots indicate fluvial environment for the Lokoja Bassange Formation, dominantly shallow marine environment for the Mamu Formation and fluvial - shallow marine environment for the Ajali Formation. This study shows that the Benin Flank, western Anambra Basin has a depositional setting radiating between fluvial and shallow marine environments.

Morphometric analysis of pebbles in verification of transport processes and interpretation of palaeoenvironment: A case study from the Ogwashi Formation (Oligocene), Niger Delta Basin, Nigeria

“…The size and shape of clastic sediments have been related to the processes of transport and deposition. It has been shown and proved that pebble morphometric parameters may be helpful, as additional indicators, in deciphering the processes of transport and depositional environment (e.g., Sneed & Folk, 1958;Lutig, 1962;Sames, 1966;Dobkins & Folk, 1970;Stratten, 1974;Gale, 1990Gale, , 2021Widera, 2010;Okoro et al, 2012;Odumodu & Israel, 2014;Ocheli et al, 2018;Madi & Ndlazi, 2020;Oluwajana et al, 2021).…”

“…Pebble morphometric analysis is a sedimentological approach that has been successfully applied by several workers for deciphering the palaeoenvironments and depositional settings of similar formations and basins in Nigeria and other parts of the world (e.g., Sames, 1966;Hubert, 1968;Dobkins & Folk, 1970;Nwajide & Hoque, 1982;Gale, 1990Gale, , 2021Olugbenro & Nwajide, 1997;Ogala et al, 2010;Widera, 2010;Okoro et al, 2012; A -A simplified regional geological surface map of the Niger Delta Basin showing the location of the studied outcrop (marked as a red star) in the northern delta area (reprinted from Ogbe, 2021); B -A schematic NE-SW cross-section through the Niger Delta Basin in south-eastern Nigeria (reprinted from Ogbe, 2021;Ogbe & Osokpor, 2021); note the position of the vertical line AB depicting stratigraphical successions in the Niger Delta Basin; for a detailed stratigraphy see Figure 2. Nton & Adamolekun, 2016;Ocheli et al, 2018;Madi & Ndlazi, 2020;Oluwajana et al, 2021). Similarly, Odumodu and Israel (2014) and Onyemesili and Odumodu (2019) used this sedimentological approach with eroded pebbles in the interpretation of the Ogwashi Formation and concluded that the sediments of this unit formed in a fluvial environment.…”

Re-examination of Hydrochemistry and Groundwater Potentials of Cross River and Imo-Kwa-Ibo Intersecting Tropical Basins of SouthSouth Nigeria

“…Most of the deep wells constructed in CRB seemed to be positioned on the Benin Formation, as the outcrops of the Ajali Formation is narrow. The aquifers of Benin Formation are confined in some places producing artesian conditions [44,[115][116][117][118] . As a result of poor groundwater conditions in CRB, people largely depend on surface water sources, waterborne diseases like guinea worm contagion, is rather widespread, especially in Abakaliki, Enyimba, and Uburu areas [44] .…”

Provenance Interpretation and Depositional Environment of Sandstones of the Ajali Formation, South of Ifon, Western Flank of Anambra Basin, Southwestern Nigeria

“…However, reports on the depositional environment and provenance of sands of the Ajali Formation on the western flank of the Anambra Basin, south of Ifon are limited. Many researchers have conducted different studies on sediments in different parts of the world to interpret the depositional process and environment of such sediments (Ocheli et al, 2018). The grain-size distribution of sediment reflects both the hydrodynamic conditions and the grain-size population of sediments available from the source area (Bjørlykke, 2010).…”

“…Tijani et al, 2010 revealed that Ajali Sandstone in the Anambra Basin was deposited under a fluvial/river system-dominated sedimentary process. Ocheli et al (2018) established a fluvial to shallow marine environment for the Ajali Sandstone in the western flank of the Anambra Basin. Ladipo (1985), Tijani et al, (2010), and Ogbahon and Opeloye (2014) observed that Ajali Sandstone has quartz greater than 90% with very little clay matrix, indicating a predominant basement source.…”