Facies and geochemical characteristics of the Igumale Formation, Lower Benue Trough, Nigeria

Abstract

This research examines the carbonates textures, chemical composition, and depositional settings of carbonate rocks collected from the Igumale region in the Lower Benue Trough, Nigeria. This approach integrates X-ray Diffraction (XRD) for mineralogical identification, X-ray Fluorescence (XRF) for geochemical characterization, and thin section petrographic examination for microfacies analysis, this research aimed to unravel the compositional attributes and interpret the paleoenvironmental conditions within these Cretaceous carbonate sediments. The petrographic analysis of the Igumale samples revealed two distinct carbonate microfacies: a sandy bioclastic wackestone, indicative of a lower energy setting with detrital siliciclastic input and significant fossil accumulation, and a micritic bioclastic packstone, suggesting a slightly higher energy environment with closely packed bioclastic grains within a fine-grained carbonate matrix. The XRD analysis revealed a substantial presence of calcite as the dominant mineral phase, underscoring the primary carbonate composition of the Igumale Formation. The XRF analysis revealed that calcium oxide (CaO) and its constituent element, calcium (Ca), as the most abundant oxide and element, respectively, further corroborating the calcitic nature of these rocks. Petrographic interpretations, based on the textural and compositional characteristics of the identified microfacies and their fossil content, strongly suggest that the Igumale Formation was deposited within a shallow marine environment, potentially transitioning into tidal flat settings, influenced by both biological activity and terrigenous input. The findings offer valuable insights into the geological history of the Lower Benue Trough, highlighting the mineralogical makeup, textural diversity, and dominant depositional environments of the carbonate rocks in the Igumale Formation, thereby enhancing the understanding of the basin's Cretaceous sedimentary development.