Foraminifera Biostratigraphy, Palynofacies and Paleoenvironment of deposition of the Albian to Santonian sediments in the Southern Benue Trough, Nigeria

Abstract

The Albian-Santonian sedimentary sequence in the Ndeaboh-Nenwe area of Enugu, Southern Benue Trough, were analysed for foraminifera and integrated with ostracod and palynofacies analyses to comprehensively appraise the age and depositional environment of the sediments. This is paramount since the studied formations have intermittent series of non-marine sedimentary influences throughout the basin. The results of foraminifera evaluation indicate that the Abakaliki Formation is barren of foraminifera species, whereas the Eze-Aku and Awgu formations have preponderance of planktonic foraminifera assemblages over benthic forms. The Eze-Aku Formation records an abundance of species of Hedbergella and a peak for Heterohelix. The co-occurrence of Whiteinella archeocretacea, Hedbergella planispira, Heterohelix delrieonsis and the ostracod species Ovocytherida symmetrica, suggests a Late Cenomanian to Early Turonian age. Rare species of short-ranging and keeled planktonic taxa are present in Awgu Formation, which has a preponderance of Heterohelix reussi, Heteroheix globulosa, Heterhelix pulchra, Whiteinella baltica, and the ostracods Brachycythere ekpo and Cythereis sp. The Awgu Formation is Middle Turonian to Santonian. The percentage of amorphous organic matter and lithologic characteristics suggest a marine environment for the Abakaliki Formation, although the water depth cannot be ascertained. In the Eze-Aku Formation, the prevalence of Hedbergella and its co-occurrence with Whiteinella and associated palynofacies data (amorphous organic matter, black debris, few structured terrestrial phytoclasts) and dinoflagellate cysts suggest a fairly deep (200–300 m) marine environment with occasional terrestrial input. The low diversity of agglutinated benthic foraminifera assemblage in the Awgu Formation indicates deposition at a minimum paleo-water depth. The paucity of benthic foraminifera, rare occurrence of keeled planktonic species, and the dominance of Hedbergella and Heterohelix; low oxygen tolerant species, in the studied interval are attributed to anaerobic bottom conditions possibly caused by poor bottom water circulation and high organic productivity in the oceans and seas during the Cenomanian-Santonian.