ABSTRACT
Heavy mineral petrographic
and geochemical compositions (major and trace/rare earth elements) of sandstones obtained from the
Oligocene-Miocene Ogwashi-Asaba Formation, Niger Delta were studied to
determine their provenance, source area weathering conditions and tectonic
setting. The heavy mineral suite (opaque minerals, zircon, tourmaline, and
rutile) revealed that the sandstones are mineralogically mature and implied
rapid disintegration and chemical decomposition of sediments mostly of recycled
orogen. The sandstones were geochemically classified as Fe-sand and partly
quartz arenitic. Chemical Index of Alteration and Chemical Index of Weathering
values of 89.92% and 91.87% respectively suggest that the source region was
predominantly felsic and was subjected to intense chemical weathering probably
under tropical palaeoclimatic conditions with abundant rainfall that enhanced
sediment recycling. Major element concentration discriminant plots also
indicated that the sediments were derived from mixed sources (granitic,
gneissic or recycled orogen) under passive margin setting. Chondrite normalized
plot of the rare earth element pattern is marked by light rare earth element
enrichment and negative Eu anomalies, interpreted to mean that provenance was
mainly continental crustal rocks. Trace elemental ratios that are provenance
diagnostic (La/Sc, Th/Sc, Cr/Th, La/Co, Th/Co, Th/Cr, Eu/Eu*, and Eu*) all
point to sediments derived from felsic source and upper continental crust. The
mixed provenance of the sandstones can be traced to the southwestern and
southeastern Basement Complex (consisting of granites, gneisses, etc.) and
sediments derived from the adjacent sedimentary basins (Anambra and Benue
Trough).