Palynostratigraphy, Palynofacies, And Organic Thermal Maturity Of The Cretaceous Sediments of Kobnaswaso - 1 Well, onshore Tano basin (Ghana)

Abstract

Particulate organic matter from sediments in the Kobnaswaso-1 well, onshore Tano Basin, Ghana was subjected to palynological analysis. Palynomorphs recovered allow for the identification of five informal biozones: Afropollis operculatus Total Range Zone (PZ-I) (?late Aptian), Elateropollenites jardinei - Sofrepites legouxiae Interval Zone (PZ-II) (early Albian to early Cenomanian), Triporites sp - Classopollis brasiliensis Interval Zone (PZ-III) (mid-late Cenomanian), Droseridites senonicus Interval Zone (PZ-IV) (late Turonian-Santonian), and Senegalinium laevigatum - Cordosphaeridium inodes - Andalusiella dubia Assemblage Zone (PZ-V) (early Campanian). PZ-I, PZ-II, and PZ-III suggest sediment deposition in relatively shallow marine habitats with vegetation growing in coastal local wetlands under semi-arid/arid climatic conditions. PZ-IV indicates the presence of rainforest trees under humid climatic conditions. PZ-V reflects sedimentation in mangrove environment under a warm humid tropical to subtropical climate. Palynofacies analysis revealed four palynofacies types: PF-1 (inner neritic zone with proximal suboxic-anoxic shelf condition), PF-2 (marginal marine setting with marginal dysoxic-anoxic basin redox condition), PF-3 (fluvio-deltaic and mud-dominated oxic shelf), and PF-4 (nearshore to shallow marine environment with dysoxic-anoxic redox condition). PF-1 is dominated by oil-prone materials (kerogen type II), while PF-2, PF-3, and PF-4 are dominated by gas-prone materials (kerogen type III). Observed Thermal Alteration Index (TAI), and Vitrinite Reflectance (Ro) indicate that, samples associated with PF-1 are thermally mature, whereas those of PF-2, PF-3, and PF-4 are considered thermally immature.