Palynological evidence for Campanian-Maastrichtian age and transitional marine environment of the Patti formation, Ahoko, southern Bida Basin, Nigeria

Abstract

A palynological study of fourteen road cut samples from the Patti Formation in Ahoko, southern Bida Basin (along the Lokoja-Abuja Expressway), was conducted to determine the age, biozone, and depositional environment of the sedimentary succession. Palynomorphs were extracted through acid digestion, while lithological characterization was performed via physical inspection and Sedlog software analysis. The study yielded 70 species of palynomorphs in varying degrees of abundance and diversity. The identified palynomorphs were dominated by both marine and land derived particles such as Senegalinium sp., Cyclonephelium sp., Paleocystodinium australinium, Paleocystodinium sp., Cyathidites sp., Cyathidites minor, Tricolporopollenites sp., and Inaperturopollenites.The recovery of age-diagnostic palynological markers in the studied intervals enabled the establishment of Senegalium sp.-Longerapertites sp. Assemblage Biozone which correlates with the Spinizonocolpites baculatus-Longerapertites sp-3 assemblage zone of Lawal and Moullade (1986) and the Echitriporites trianguliformis-trianguliformis-Scabratriporites annellus palynological zone of Salard Cheboldaeff (1990). Thus, a Campanian to Maastrichtian age, in the Late Cretaceous, has been assigned to the section. Based on lithology, the formation consists predominantly of black carbonaceous shales, yellowish siltstones and ironstones overlain by minor claystone layers. The integrated data infer a mixed marine-terrestrial environment during deposition, supported by abundant marine dinoflagellate cysts and terrestrial palynomorphs.