Trace Fossils and Paleoenvironments of the Turonian Amasiri (Afikpo Synclinorium) and Campanian Afikpo Sandstone Facies (Afikpo Sub-Basin), Southeastern Nigeria

Abstract

This study evaluated trace fossils and lithofacies of the Turonian Amasiri (Afikpo Synclinorium) and Campanian Afikpo Sandstone facies (Afikpo Sub-basin), southeastern Nigeria. The lithofacies and ichnofossils, distribution, and ichnofabric index were used to interpret paleoenvironments of deposition for the sandstone units. The trace fossils recorded in the Amasiri Sandstone includes Ophiomorpha irregulaire of the Skolithos ichnofacies; Thalassinoides, Planolites, Paraonis, Monocraterion, Palaeophycus and Arthrophycus belonging to the Cruziana ichnofacies. The Afikpo Sandstone is characterised by Skolithos, Arenicolites, Ophiomorpha nodosa, and Chondrites, Rosselia, Thalassinoides, Planolites belonging to Skolithos and Cruziana ichnofacies respectively. The trace fossil assemblages of Skolithos and Cruziana ichnofacies are characteristic ichnofacies of both lower and high energy conditions in shallow water sand environments. The ethological categorisation of the ichnofossils shows that feeding and dwelling traces occur in the sandstone facies. The facies include bioturbated sandstone, cross-bedded sandstone, laminated sandstone, thin-bedded sandstone, massive/ conglomeritic sandstone facies for the Amasiri Sandstone, while bioturbated sandstone, cross-bedded sandstone, bioturbated cross-bedded sandstone and sandy heterolith were recorded in the Afikpo Sandstone. The gross paleoenvironments of deposition deduced from the trace fossil assemblages and lithofacies/ association suggests that the Amasiri Sandstone facies were deposited in foreshore to offshore settings; while the Afikpo Sandstone facies were deposited in estuarine and foreshore environments. The general absence of Zoophycos-Nereites ichnofacies (deep water ichnofacies) in the sandstone facies indicates the Turonian and Campanian epeiric seas were shallow.

Publication Info:

Author: Igwe, E.O. and Obasi, A.I.

Volume: 57

Issue: September

Published By: Journal of Mining and Geology, 2024-09-01