Lithofacies, particle size analysis and paleodepositional environment of the Eze-Aku Group (Cenomanian–Turonian) in the Itigidi-Ediba area, Afikpo Synclinorium, southeastern Nigeria

Abstract

Field, lithofacies and particle size analysis of sediments of the Eze-Aku Group in the Itigidi-Ediba localities, Afikpo Synclinorium, were carried out to describe the textural attributes of the sediments and reconstruct the paleodepositional environment of the study area. Field studies show that the geology is characterized by a succession of marine shales and shaly-limestone overlain by elongate sandstone ridges that trend in a northeast–southwest direction. In certain cases, the sandstone ridges alternate with shales. These deposits are characterized by wave and tide generated sedimentary structures with trace fossil assemblages consisting mainly of Ophiomorpha, Skolithos, and Cruziana ichnofacies that are suggestive of a moderately disturbed environment. Lithofacies studies of the sedimentary succession indicates five facies associations: conglomeritic consolidated sandstone, laminated sandstone, bioturbated sandstone, laminated shaly-limestone and cross-bedded sandstone facies associations suggesting deposition in proximal sub-marine, shelf edge/sub-marine fan, distal sub-marine fan/distal shelf, shallow/deep marine, and shoreface/foreshore sub-environments, respectively indicating a tidal shallow shelf to deep marine environment. Analysis of the grain size spectrum in some selected outcrops shows sediments that are moderate to poorly sorted, generally positively and very positively skewed and mesokurtic, platykurtic to leptokurtic, deposited in a shallow marine environment under moderate to high energy conditions, with fluvial influence.