Providing Clues on the Paleo-weathering of Ogwashi Asaba Formation, Niger Delta Basin: Evidence from Geochemistry
Overare, B. and Osokpor, J. Keywords: Paleo-weathering, Weathering indices, Major oxides, Niger Delta, Ogwashi-Asaba Formation
Tropical Journal of Science and Technology 2020 1(1), 74-92. Published: June 29, 2020
Representative outcrop samples of sandstones belonging to the Ogwashi-Asaba Formation, Niger Delta, were investigated using geochemical proxies. The purpose was to appraise the paleo-weathering as well as to infer the paleoclimatic conditions that prevailed during their deposition. The sediments are geochemically classified as sublithic arenites, quartz arenites, and Fe- sands. The relative depletion of most major elements in the sandstones suggests high mobility during weathering processes. High values of weathering indices such as Chemical Index of Alteration (CIA: 95.21–95.90; 95.65±0.24), Chemical Index of Weathering (CIW: 96.01–96.64; 96.43 ± 0.22), Plagioclase Index of Alteration (PIA: 95.98–96.61; 96.40 ± 0.22), Mineralogical index of alteration (MIA): 90.42–91.79, 91.29 ± 0.48) and low values of the Weathering index of Parker (WIP): 13.37 – 19.08; 17.04±2.59 ) suggests intense weathering in the source area. The intense degree of weathering was further affirmed by the Al2O3-(CaO+Na2O)-K2O ternary relationship and the CIA versus SiO2 correlations. A warm/humid climate is suggested for the sandstones based on the CIA values and the SiO2 vs. (Al2O3 + K2O + Na2O) correlation, which is widely used for paleoclimatic studies. Weathering indices that include iron in their calculations were not included in this investigation since they do not distinguish between ferric and ferrous iron.