Abstract: The geochemistry, classification and maturity of the Eocene Nanka Formation were investigated. The sandstones are non-calcareous, ferromagnesian potassic sandstones composed of sublitharenites and quartz arenites. Plot of SiO2/Al2O3 against quartz / (feldspar + lithic fragments) indicates compositional maturity. SiO2/Al2O3 and Fe2O3/K2O values are high, implying mineralogical maturity and low degree of clayness and presence of stable mobile oxides. The minute alkali content indicates the near absence of feldspar and high chemical maturity. The ZTR values suggests that the sediments are mineralogically immature to sub mature, however, the mineralogical maturity index classifies the Nanka sandstone as mature to super mature. A decrease in the abundance of TiO2, Fe2O3, CaO, Na2O, MgO, MnO, K2O, and Al2O3 as SiO2 increases is due to chemical weathering and removal of these elements. There is no correlation between K2O and TiO2 suggesting a loss of K2O and an indication of diagenetic alteration of feldspars. There is no correlation with Na; the extrapolated regression equation did not pass through the origin, suggesting minimal Na2O contribution from the clay minerals. There is no correlation between TiO2 and Al2O3 due to depositional process and granulometry; indicating that TiO2 is not associated with phyllosilicates. TiO2/Al2O3 ratio is low indicating that the sandstone matrix is composed of clay minerals. There is no correlation between K2O and Al2O3 due to changes in the quartz-matrix proportions reflecting the grading. The Al—Ti—Zr ternary plot and the wide range of TiO2/Zr variations, indicates compositional maturity, good sorting trend, rapid deposition and low to medium Zr concentration Keywords: Eocene, mineralogical maturity index, quartz, sandstones, ZTR index. Title: GEOCHEMISTRY, CLASSIFICATION AND MATURITY OF THE EOCENE NANKA FORMATION SOUTH EAST, NIGERIA Author: Henry Y. Madukwe, Matthew A. Adeniran, Paulinus N. Nnabo International Journal of Recent Research in Interdisciplinary Sciences (IJRRIS) ISSN 2350-1049 Vol. 10, Issue 2, April 2023 - June 2023 Page No: 41-57 Paper Publications Website: www.paperpublications.org Published Date: 02-June-2023 DOI: https://doi.org/10.5281/zenodo.7997489 Paper Download Link (Source) https://www.paperpublications.org/upload/book/GEOCHEMISTRY,%20CLASSIFICATION-02062023-4.pdf

International Journal of Recent Research in Interdisciplinary Sciences (IJRRIS), ISSN 2350-1049, Paper Publications, Website: www.paperpublications.org