PALYNOFACIES, PALEOENVIRONMENT AND SEDIMENTATION RATE ANALYSES OF KUDU-3 WELL, BIDA BASIN, NIGERIA

Abstract

This study describes the palynofacies analyses carried out on nineteen ditch cutting samples within the depth interval of 31 – 58 m (27 m thick) from Kudu-3 well, Bida Basin with the view to assess the palynofacies, palaeoenvironment of deposition and sedimentation rate. Lithologic description shows that the lithology of the studied interval consists of silty mudstone, sandy mudstone, siltstone and sandy siltstone lithologic units, indicating Enagi Siltstone. Acid methods for recovery of particulate organic matter from samples were followed. The analyses yielded low to moderate recovery of dinocysts, pollen and spores, small to large sizes of palynomaceral1 (irregularly shaped, orange-brown to dark-brown coloured and opaque plant debris), palynomaceral 2 (irregularly shaped, brown-orange coloured platy plant materials), and few occurrences of palynomaceral 3 (pale to brown coloured, cuticular, and translucent plant materials) and palynomaceral 4 (black to dark brown coloured, blade/needle like shaped plant materials). Paleoenvironment and bathymetric interpretation using palynological marine index (PMI), environmental diagnostic taxa and palynomacerals show that the studied interval was deposited in fresh water to brackish water environment. The presence of inner neritic dinoflagellate cysts such as Palaeocystodinium sp., Achosmosphaeridium sp., Oligospheridium sp., Leiosphaeridia sp., and Oligospheridium complex suggest marine influence within the bathymetric range of 0 – 20 m (upper-shoreface to lower-shoreface). The rate of sedimentation interpretation using number/percentage of well-preserved palynomorph forms recovered per depth suggests low rate of sedimentation (0.5 cm/1000 years) to relatively high rate of sedimentation (30 cm/1000 years) within the studied interval since hemipelagic accumulation rate is in the range of 5 – 300 mm/1000 years. Brackish water environment and high rate of sedimentation support significant deposition and accumulation of organic matter, quick burial and hydrocarbon generation