Facies and Depositional Environment of the Eze-Aku Formation in Ebonyi State

The Eze-Aku Formation, a significant Turonian marine succession cropping out extensively in Ebonyi State, South East Nigeria, contains alternating sequences of calcareous shales, limestones, and siltstones that record important information about Cretaceous marine conditions in the Benue Trough. This study undertakes a detailed facies and depositional environment analysis of the Eze-Aku Formation at selected outcrop localities in Ebonyi State. Measured stratigraphic sections were constructed at three locations, documenting lithological descriptions, sedimentary structures, bed geometry, and fossil content. Facies were defined on the basis of recurring lithological and textural attributes, and facies associations were interpreted in terms of depositional sub-environments within a shallow to mid-shelf carbonate-siliciclastic setting. Thin section petrography of limestone samples identified microfacies types including wackestones, packstones, and mudstones, which were interpreted using the Dunham classification. Trace fossil assemblages were documented to assess substrate conditions and oxygenation, with ichnofabric index applied where preservation permitted. Geochemical proxies including carbon and oxygen isotope ratios were measured on selected limestone samples to infer palaeotemperature and palaeosalinity variations. The study provides a well-documented stratigraphic framework for the formation in Ebonyi State and contributes to understanding of Cretaceous palaeoceanographic conditions in this part of the Benue Trough. Keywords: Eze-Aku Formation, facies analysis, Cretaceous, Ebonyi State, depositional environment.