अमूर्त

PALYNOLOGICAL STUDIES OF UPPER CRETACEOUS SUCCESSION OF HERWA-1 WELL, CENTRAL CHAD BASIN, NIGERIA

Oloto, I.N . Yikarebogha,Y . Omoboriowo, A.O

The Late Cretaceous succession penetrated by Herwa-1well in the Central Chad Basin, North East Nigeria was investigated for its palynological content. This investigation produced biostratigraphically significant Pollen, Spore and dinoflagellate cyst. The studied interval penetrated a sequence of clay, sandstone, shale, shally sandstone, sandy shale and sandstone, occuriing at different intervals in all the wells. Based on the stratigraphic distribution of the palynomorphs from the Herwa-1 –well. Twelve informal assemblage palynozones and six dinoflagellate assemblage biozones spanning the Upper Cretaceous were identified in the Chad Basin, Nigeria. The zones are: Assemblage Zones I-IV (Cenomanian); Assemblage Zone V (Turonian); Assemblage Zone VI,VII,VIII, and IX (Coniacian-Santonian); and Assemblage Zones X,XI, XII, and XIII (Campanian-Maastrichtian) for the Pollen/Spore biozones.. The age determinations are based on the known stratigraphic ranges of pollen, spores and dinoflagellate and their relative stratigraphic positions. Data from the studied well revealed that generally in the basin, there is relatively higher frequency of the land derived pollen and spores compared to marine palynomorph abundance, which suggests a paralic condition of continental to shallow marine environment. The shallow marginal marine environment is further supported by the presence high diversity of dinoflagellate species and foram test linings at some depths which are indicative of marine paleoenvironment i.e. neritic environment.