Inorganic geochemical and sedimentological evaluation of some shales in the Campano-Maastrictian formations of Anambra Basin

Abstract

This study presents an insight into the sediment provenance, paleoenvironment and conditions of deposition of Mamu Formation and Nkporo Group shales. To achieve this, sedimentologic and geochemical study of shale sequences from the Mamu and Nkporo group were carried out. Twenty five representative shale samples from these formations were subjected to sedimentologic, geochemical and mineralogical analyses using hydrometric method and Atomic Absorption Spectrophotometry (AAS). The results show that for the particles size analyses of sediments, the samples reveal medium grained with average sand, silt and clay values ranging from 33.1-54.7%, 29.08-52.1%, 8.0-16.48% respectively. The overall classification of the samples can be said to be poorly sorted sediments with low energy of deposition. The qualitative and quantitative analyses of the major elements namely SiO₂ (56.99% and 51.6%), Al₂O₃ (29.09% and 28.28%) and Fe₂O₃ (3.13% and 4.38%) for Mamu and Nkporo shales respectively indicate high detrital influx. While the positive correlation plots for SiO₂ against Al₂O₃, TiO₂ and K₂O are indicative of transported clay mineral units. The SiO₂/Al₂O₃ ratios observed for Nkporo shales can be said to be pure Kaolinite, while those for Mamu shales are both Kaolinite and Montmorrillonite.

Keywords: sedimentologic, geochemical, shales, analyses, clay minerals