Palynological and Paleoenvironmental Study of Paleogene in Bende – Umuahia, Niger Delta Basin, Nigeria

摘要

Palynological and paleoenvironmental study of outcrops exposed around Bende and Umuahia areas were carried out to re-evaluate its age and reconstruct the environment of deposition. Palynological analysis of the sediments was done by using conventional method of 40% concentrated Hydrofluoric acid maceration to determine the age and paleoenvironment of the area. Lithological units encountered were carbonaceous shale, sandstones, mudstones and limestone. Age determination/correlation was based on occurrence of stratigraphically significant age diagnostic palynomorph assemblages. Imo Formation was dated Middle – Late Paleocene with the following index fossils assemblage, Proxapertites operculatus, Echitriporites trianguliformis, Retibrevitricolpites triagulatus, Spinizonocolpites baculatus, Scabratriporites simpliformis, Mauritidiites crassibaculatus, Bombacidites sp., and Grimsdalea polygonalis . Ameki Formation was assigned Early-Middle Eocene based on Monoporites annulatus, Proxapertites cursus, Retistephanocolpites williamsi, Ctenolophonidites costatus, Spinizonocolpites echinatus, Psilatricoplorites crassus, Psilatricolporites operculatus, Retitricolporites irregularis, and Striatopollis sp . Ogwashi Formation was dated Late Eocene-Oligocene on the basis of the age-diagnostic sporomorphs assemblage, such as, Verrucatosporites usmensis, Laevigatosporites ovatus, Chenopodipollis sp., Retibrevitricolporites sp., Psilastephanocolporites sp., and Racemonocolpites hians . The environmentally significant palynomorphs species indicate that Imo Formation was deposited in a tidally-influenced shallow marine estuarine setting, while Ameki Formation was deposited in open shallow marine to estuarine-lagoonal settings. Ogwashi Formation was deposited between upper to lower deltaic settings. The palynological study suggests Formtions of Paleogene Age while the paleoenvironment is Deltaic to Shallow-marine.