Organic walled dinoflagellate cyst biostratigraphy of the middle-late Miocene western Niger Delta, Nigeria

Palynological analysis of 200 ditch cuttings of wells M6 and M7 from the western Niger Delta yield a diverse assemblage of pollen, spores, freshwater algae, foraminiferal wall linings and dinoflagellate cysts. Based on pollen and spore marker species, the wells date middle – late Miocene (P720-P860). The regular occurrence of dinoflagellate cysts enhances the subdivision of the sequences into eight and seven tentative dinoflagellate cysts assemblage zones for the M6 and M7 wells respectively. The proposed Niger Delta Dinoflagellate Cysts (C-I) zones are viz: the Lingulodinium machaerophorum Assemblage zone; Homotryblium spp./Sumatradinium spp. Assemblage zone; Operculodinium centrocarpum Assemblage zone; Nematosphaeropsis labyrinthus Assemblage zone; and the Protoperidinium spp./Selenopemphix spp. Assemblage zone. The boundaries are marked by remarkable dinocysts events such as first downhole occurrences or highest stratigraphic occurrences, supplemented with last downhole occurrences or lowest stratigraphic occurrences as the samples were ditch cuttings. The common presence of dinoflagellate cysts and the dominance of Nematosphaeropsis labyrinthus and Impagidinium spp. indicate open marine conditions during the deposition of the studied section.