Lithofacies, Palynology and Paleoenvironmental Study of Campanian to Late Maastrichtian Deposits of Ogbabu-1 well Anambra Basin, South Eastern Nigeria

Lithofacies, Palynology and Paleoenvironmental Study of Campanian to Late Maastrichtian Deposits of Ogbabu-1 well Anambra Basin was carried out using ninety (90) ditch cutting samples ranging in depths 1000ft - 6830ft (305m - 2080m), with the aim of giving a detailed palynological analysis of the formations penetrated by Ogbabu-1 Well in Anambra Basin using sedimentology and palynology as geologic tools. This was achieved by identifying the different species of palynomorphs present as well as their range, the lithologic unit, age, different biozones and paleoenvironment of deposition. The sedimentological analysis was used to define Lithofacies zones and identify minerals. The main lithologies encountered in the well consist of shaly sands; sandy shales, shales and sand. Fourteen (14) Lithofacies zones were established. Minerals identified include feldspar, iron oxide and mica. Six hundred and sixty one (661) palynomorphs species were recovered. Five hundred and eighty five (585) were Miospore (pollen and spore) and seventy six (76) Dinocysts. The identified minerals obtained from the sedimentological analysis was used to argument data from palynological analysis to establish paleoenvironmental events. The absence of Danian diagnostic dinocysts especially Damasadinium californicum and Carpatella cornatus respectively suggest a Maastrichtian age for the well section between 1000ft-6600ft. The age of the well penetrated was inferred to range from Campanian to Late Maastrichtian. Late Maastrichtian age (1000-3550ft), top of this zone is undefined because of absence of data but the base of the zone is defined by the last appearance datum of Cingulatisporites ornatus (3550ft). Middle Maastrichtian age (4050ft-5080ft) established based on top of the zone is marked by the base of preceding zone. The zone is also marked by last appearance datum of Classopollis spp. (4930ft). Early Maastrichtian age (5240ft- 6600ft) established based on the last appearance datum of Ctenolophonidites costatus (6600ft) and the base is defined by the first appearance datum of Constructipollenites ineffectus (6600ft). Campanian age (6700-6830ft) established based on the last appearance datum of Triorites africaensis (6700ft). The formations likely penetrated by the well section are the Nkporo shale (Campanian) and the Ajali Sandstone (Maastrichtian age). The well section (1000ft – 6380ft) was delineated to be shallow marine environment.

Keywords
Lithozones; Campanian-Late Maastrichtian; Anambra Basin; Palynomorphs; Formation