Classification, Maturity, Provenance, Tectonic Setting and Source-Area Weathering of the Ilubirin Stream Sediments, South West, Nigeria

Geochemical study on the Ilubirin stream sediments was carried out to infer their provenance, maturity, classification, enrichment, depletion, tectonic setting and source-area weathering. The sediments can be classified as ferromagnesian potassic, quartz arenites that are non-calcareous. The SiO 2 /Al 2 O 3 index is high, meaning that the samples are mature, the Index of Compositional Variability also indicate that the sediments are mineralogically mature, while the Al 2 O 3 /(CaO+MgO+Na 2 O+K 2 O) ratio indicate that there are stable mobile oxides in the sediments. The plot of SiO 2 versus Al 2 O 3 + K 2 O+ Na 2 O shows that the sediments formed under semi-arid/arid conditions tending towards increasing chemical maturity. Al 2 O 3 correlates positively with all the major oxides except SiO 2 , suggesting hydraulic fractionation and sorting. The negative linear trend between Al 2 O 3 and SiO 2 indicates that the major element composition of the stream sediments is controlled largely by the relative amount of quartz and feldspar versus clay minerals. The depletion of highly mobile Na. K and Ca elements is due to leaching during the formation of clay minerals during increased chemical weathering. The immobile Fe and the less mobile Mg elements were depleted while the immobile Ti was enriched; this suggest that they may are from a felsic source. The high TiO 2 /Fe 2 O 3 ratios suggests concentration in the sediments of a heavy mineral phase containing Ti minerals such as ilmenite and rutile. The weathering indices (CIA, CIW, PIA and MIA) indicates a high degree of weathering of the source materials. The tectonic setting is the passive continental margin, while the provenance is the quartz-rich sediments of mature continental provenance, associated with a continental passive margin, intracratonic basins, or recycled orogenic provinces.