Paleoenvironmental and paleoclimatic reconstruction of the umu-5 well, niger delta basin, using lithofacies and palynological evidence

Abstract

This study presents an integrated lithofacies, palynological, palynostratigraphic, and palynofacies investigation of the UMU-5 well (5500–11560 ft) in the Niger Delta Basin, with the objective of reconstructing the stratigraphic framework, paleoenvironment of deposition, paleoclimate, and hydrocarbon potential. Twenty five ditch cutting samples were analysed using standard palynological preparation and microscopic techniques. Five lithofacies were identified: shaly sandstone (52%), mudstone (12%), sandy shale (12%), clayey sandstone (4%), and claystone in the basal sections. Shaly sandstone, the dominant facies, is interbedded with mudstone and sandy shale, reflecting fluctuating energy conditions typical of delta front and shallow marine settings. Palynological analysis revealed diverse assemblages of pollen, spores, dinoflagellate cysts, and freshwater algae, dominated by terrestrial taxa such as Zonocostites ramonae and Acrostichum aureum. Three informal biozones (U-I, U-II, and U-III) were established using key marker species including Belskipollis elegans, Crassoretitriletes vanraadshoveni, and Echiperiporites estelae, correlating with the P720, P740, and P770 subzones of Evamy et al. (1978) and assigning a Middle Miocene (Langhian–Serravallian) age to the studied interval. Palynofacies analysis indicates the predominance of Palynomaceral types I, II, and IV, with subordinate type III and moderate occurrences of structureless organic matter. Ternary plot results place the samples within Field V, reflecting deposition under oxic conditions with limited preservation of amorphous organic matter. Paleoenvironmental interpretation indicates a marginal marine setting influenced by strong fluvial input, while paleoclimatic reconstruction suggests a warm, humid tropical climate characterised by high rainfall, dense vegetation, and widespread mangrove and freshwater swamp development during the Middle Miocene. Organic matter is predominantly terrestrial (Type III kerogen), indicating gas prone hydrocarbon potential with limited source rock quality.