Analysis of the Palynostratigraphy and Unconformity Contact Prototype of the Ogwashi Formation of the Outcropping Niger Delta Basin at Ogbunike

Abstract

The palynostratigraphy, nontectonic unconformity contact and perceived nonexistence of the geologic attributes of the Ogwashi Formation in the stratotype section and point (SSP) ofthe formation instigated a paradigm shift in the appraisal of the age, paleoenvironment and unconformity between the Nanka and Ogwashi formations. The palynological composition and stratigraphic ranges of the recovered palynomorph species suggest an age of Pariabonian to Aquitanian for the Ogwashi Formation based on the occurrence of Pachydermitesdiederixi, Striamonocolpitesrectostriatus, Crassoretitriletesvanraadshooveni, Peregrinipollisnigericus, Auricculopollenites group, Periretipollis spinosus, Doulaiditeslaevigatus, Racemonocolpiteshians and Verrutricolporites irregularis. The Ypresian to BartonianNanka Formation in the vicinity is barren of palynomorphs.The palynomorph hydrodynamics and lithological attributes of the Ogwashi Formation illustrate an oscillating coastal plain and brackish water depositional setting while the Nanka Formation depicts tidal river plain settings oscillating from subtidal and intertidal paleoenvironment conditions. The unconformity attributes of the Ogwashi and Nanka formations depict a confirmed buttress unconformity (onlap unconformity) while the unconformity unit stratotype illustrates the lower limits of a unit Ogwashi Formation stratotype and the upper limits of the Nanka Formation of the Ameki Group. Thisportrays a sequence of non-deposition within the Nanka Formation unparallel to the unconformity andtruncation of the younger layers of the Ogwashi Formation at the unconformity surface. This substantiates the Ogbunike section of the Ogwashi Formation as a definite unit boundary stratotype, and lower unit stratotype and lower unit type section model of the formation. The age, paleoenvironments and unconformity of the study illustrate a general active nontectonic depositional contact along with penecontemporaneous and gravity-slide structures associatedwith thedelta during the Cenozoic.

Publication Info:

Author: Okeke, K.K.

Volume: 61

Issue: September

Published By: Journal of Mining and Geology Vol. 61(1) 2025. pp. 1 - 14, 2025-01-09