Lithofacies,palynofacies, and sequence stratigraphy of Palaeogene strata in Southeastern Nigeria |
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| Institution: | 1. Department of Physics, Earth and Environmental Sciences, University of Siena, Via Laterina, 8, 53100 Siena, Italy;2. Centre for Geotechnologies, University of Siena, Via Vetri Vecchi, 34, 52027 San Giovanni Valdarno (AR), Italy;3. Antarctica National Museum, University of Siena, Via Laterina, 8, 53100 Siena, Italy;4. Department of Physics and Geology, University of Perugia, Via Pascoli, 06123 Perugia, Italy;5. Department of Geological Sciences, University of Roma Tre, Largo S. Leonardo Murialdo, 1, 00146 Roma, Italy;6. KOPRI, Division of Earth-System Sciences, Korea Polar Research Institute, Songdomirae-ro 26, Yeonsu-gu, 21990, Incheon, South Korea |
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| Abstract: | 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. |
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