Lithofacies, palynofacies, and sequence stratigraphy of Palaeogene strata in Southeastern Nigeria

• Published in: Journal of African earth sciences (1994) 2005, Vol.41 (1), p.79-101
• Main Authors: Oboh-Ikuenobe, Francisca E., Obi, Chuks G., Jaramillo, Carlos A.
• Format: Article
• Language: English
• Subjects: Anambra basin; Lithofacies; Palaeogene; Palynofacies; Sequence stratigraphy; Southeastern Nigeria
• ISSN: 1464-343X; 1879-1956
• DOI: 10.1016/j.jafrearsci.2005.02.002

Integrated sedimentologic, macrofossil, trace fossil, and palynofacies data from Paleocene-Middle Eocene outcrops document a comprehensive sequence stratigraphy in the Anambra Basin/Afikpo Syncline complex of southeastern Nigeria. Four lithofacies associations occur: (1) lithofacies association I is characterized by fluvial channel and/or tidally influenced fluvial channel sediments; (2) lithofacies association II ( Glossifungites and Skolithos ichnofacies) is estuarine and/or proximal lagoonal in origin; (3) lithofacies association III ( Skolithos and Cruziana ichnofacies) is from the distal lagoon to shallow shelf; and (4) shoreface and foreshore sediments ( Skolithos ichnofacies) comprise lithofacies association IV. Five depositional sequences, one in the Upper Nsukka Formation (Paleocene), two in the Imo Formation (Paleocene), and one each in the Ameki Group and Ogwashi-Asaba Formation (Eocene), are identified. Each sequence is bounded by a type-1 sequence boundary, and contains a basal fluvio-marine portion representing the transgressive systems tract, which is succeeded by shoreface and foreshore deposits of the highstand systems tract. In the study area, the outcropping Ogwashi-Asaba Formation is composed of non-marine/coastal aggradational deposits representing the early transgressive systems tract. The occurrence of the estuarine cycles in the Palaeogene succession is interpreted as evidence of significant relative sea level fluctuations, and the presence of type-1 sequence boundaries may well be the stratigraphic signature of major drops in relative sea level during the Paleocene and Eocene. Sequence architecture appears to have been tectono-eustatically controlled.