LITHOFACIES AND PALYNOLOGICAL STUDIES OF ENUGU AND MAMU FORMATIONS EXPOSED AT AGU-ABOR AREA, ENUGU, SOUTH EASTERN NIGERIA.

Abstract

Lithofacies and palynological studies of Enugu and Mamu Formations were carried out at Agu-Abor area of Enugu, Southeastern Nigeria, with the aim to identify and document the fossil assemblages in order to establish the age and paleoenvironment of deposition. The lithologic units identified consist of shales, siltstones and sandstones. The coarsening upward sequence of the lithofacies of Mamu Formation is an indication of decrease in sea level, and the intercalation of siltstone/sandstone and shale in the lithofacies of Enugu Shale suggest a shallow-marine environment with tidal influence. Sedimentary structures observed in the formations include wave ripple lamination, parallel lamination, cross lamination and widespread burrows by trace fossils such as Planoliths and Skolithos. The palynological analysis carried out on forty (40) samples across Enugu and Mamu Formations yielded forty seven (47) spores/pollens and marine dinoflagelates that are of Early Campanian to Mid Maastrichtian for Enugu Shale and Middle Maastrichtian for Mamu Formation. The main diagnostic species of spores and pollen that show high abundance recovered include; Monocolpites marginatus, Longapertites, Retidiporites magdalenensis, Buttinea andrevii, Zlivisporites blanensis, Operculodium centrocarpum, Cingulatisporites ornatus Spinozonocolpites baculatus, Laevigatosporites sp, Leiotriletes adriennis, Echitriporites trianguliformis, Longapertites marginatus and Cyathidites minor. Among the main diagnostic dinoflagellates are Cleistosphaeridium sp, Diphes colligerum, lingulodium machaerophorum, Oligosphaeridium and Microforaminiferal wall lining. The relatively high abundance and diversity of spores and pollen in the formations is indicative of a tidally influenced shallow marine to coastal swamp environment. The dinoflagellate distribution marked instances of fully marine conditions,an assertion which is supported by PMI value above the threshold 100. The inferred ecozones are mangrove vegetation and back mangrove vegetation based on the abundance of mangrove elements such as spinizonocolpites and longapertites group for the two Formations.