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

M.E. Okiotor, O.I. Imasuen, D.E. Ogueh

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




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