MAJOR, TRACE, AND RARE EARTH ELEMENTS GEOCHEMISTRY OF THE LATE PALEOCENE SHALES FROM GAMBA FORMATION, SOKOTO BASIN, NORTHWEST NIGERIA

Abstract

The present investigation delved into the geochemical importance of trace elements and major oxide constituents in the shales from the Gamba Formation, Sokoto Basin, Nigeria. by inductively coupled plasma-mass spectrometry (ICP-MS), x-ray fluorescence spectroscopy (XRF), and statistical methodologies within the context of provenance, tectonic environments, and conditions of deposition. Alkali metals and alkali-earth metal elements, Na, K, Ca, and Mg occurred in very high concentrations in the shale samples while U has the lowest values, indicating the detritus derived from various provenances (felsic and mafic) and reducing conditions of the environment. Among the rare earth elements detected in the shales, light rare earth elements showed enriched concentrations compared to heavy rare earth elements, indicating anoxic conditions. Among the major oxides identified, the shales exhibit elevated levels of SiO2, with Fe2O3 greater than Al2O3; whereas the remaining oxides demonstrate relatively low concentrations. This suggests that shales are predominantly constituted of quartz minerals and were formed in marine settings. Moreover, the distribution patterns of the trace elements and major oxides showed striking similarities in the spider diagrams of UCC and PAAS. The ratios derived from both the trace elements and major oxides, along with the discrimination diagrams, indicated that the shales consist of mafic and felsic detritus. They were likely deposited under varying conditions, such as anoxic and oxic, near the passive margin and continental island arc. These conclusions were further corroborated by the multivariate statistical analyses conducted on the elemental dataset. This study demonstrated the effectiveness of trace elements and major oxides geochemistry in assessing the origin, tectonic setting, and paleoenvironments of shales.