This work describes the nature of rocks, tectonic setting and paleoenvironmental conditions of the upper Cretaceous grayish - dark shale from an offshore well-X from Dahomey Basin, Nigeria. The selected samples were analyzed using x-ray fluorescence analysis. Indices obtained from various ratios were used for some deductions and interpreted using plots based on some previous works. By plotting Al2O3/TiO2 againstSiO2,and also TiO2 plotted against Zr, it was indicated that an intermediate igneous rocks were the parent rock of the analyzed shales. Using the plot of K2O/Na2O and SiO2 (Roserand Korsch, 1986), an intracratonic nature of the basin was indicated.
Ratios of Cu/Zn and Cr/Ni in this work range from 0.23 to 0.63 and 1.61 to 2.55 respectively and these indicate an oxidizing condition of deposition. Additionally, chemical index of weathering (CIW) and plagioclase index of alteration (PIA) values (58.36-86.53 and 33.43-84.09 respectively) indicated a higher degree of weathering of at the source area compared to the extent of weathering inferred from our CIA values.
Key words: Provenance, offshore Dahomey Basin, mudrocks intervals, XRF, geochemical assessment.