Sedimentology and depositional environments of Yolde formation in Ngurore and environs, Yola sub-basin, Northeastern Nigeria

Abstract

The mature basin (The Niger Delta) is no longer the main focus of hydrocarbon exploration in Nigeria; instead, it is the frontier and inland basins, which include the Benue Trough. As a result, every piece of information is crucial in the search for hydrocarbons in the Yola sub-basin, and sedimentology is one of the diverse range of tools used to increase our understanding of an area's geology and paleoenvironment. Using integrated lithofacies, sieving, and petrographic investigations, this work aims to describe the geology and identify the sub-depositional environment under the more general transitional environment in the studied area. The Yolde Formation in the study area reveals a fining upward facies sequence with trough, planar, parallel, and hummocky cross beds, which are capped with interbedded fine-grained ripple sandstones and mudstones. The samples are poorly sorted, which is a sign that the sediments were subjected to fluctuating energy conditions and were texturally submatured. From the petrography, the samples in the studied area had a modal mineralogical composition that ranges from 74% to 85% quartz, 13% to 22% feldspar, and 2% to 4% rock fragments, which are subangular to subrounded. Based on the mineralogical percentages of the grains as displayed on Folk's classification scheme, they were categorized as arkose to subarkose sandstones, and the sandstone has an immature to sub-mature class mineralogical maturity index. The sub-environment of the studied area was ascertained through the integration of petrography, bivariate plots, and field work. The integration points to a series of sub-environments ranging from fluvial (braided river) to transitional (beach, deltaic, and tidal flat).