Palynofloral and dinoflagellate cysts changes in Afikpo syncline during the cretaceous period

This study presents a comprehensive palynological and kerogen analysis of the shale samples from the Afikpo Syncline, southeastern Nigeria. The main aim of this study is to determine the age, paleoenvironmental conditions, and hydrocarbon potential of the major outcrop exposure in the study area. The conventional palynological preparation technique was used to extract the palynormorphs and a diverse assemblage of terrestrial spores, pollen, and marine dinoflagellate cysts were recovered and quantitatively assessed. The palynomorph assemblages were dominated by terrestrial spores and pollen alongside marine dinocysts. The palynological association indicates mangrove affinities and a depositional environment oscillating between marginal marine proximal estuaries and shallow open marine shelf settings under predominantly brackish to normal marine salinities. Biostratigraphic correlation based on key miospore and dinoflagellate marker species, such as  Longapertites vaneedenburgi, Psilatricolporites operculatus, Proxapertites operculatus, Retidiporites magdalenensis, Spiniferites pseudofurcatus, Diphyescolligerum, Andalusiella polymopha, Spinizonocolpites baculatus, Proteacidites miniporatus, Mauritidiites crassibaculatus, Proxapertites cursus, Echitriporites trianguliformis, Longapertites marginatus, and Dinogymnium acuminatum, were used to constrain the sediments to the Campanian-Maastrichtian age, consistent with other Campano-Maastrichtian sequences across tropical Africa and coeval basins globally. Quantitative kerogen result reveals a predominance of terrestrial-derived organic matter phytoclasts and opaques up to 80% with subordinate amorphous organic matter and palynomorphs, indicating a kerogen assemblage dominated by Type III and IV kerogens, typical of gas-prone source rocks but with potential for mixed oil generation in oxic to suboxic depositional settings. Thermal maturation inferred from spore coloration suggests early to mid-maturity stages, highlighting viable hydrocarbon generation potential. The integration of palynofacies data with paleoecological indicators provides basis for depositional environment reconstructions and contributing valuable insights into the palynofloral evolution of the Afikpo Syncline and its petroleum system implications.