Geochemistry of claystones of the Ruteh Formation, NW Iran: Implications for provenance, source-area weathering, and, paleo-redox conditions

The Cherchaveh claystones (east of Bukan, West-Azarbaidjan, NW Iran) embedded as discontinuous layers and lenses within carbonates of the Ruteh Formation (upper Permian) were studied for mineralogy and geochemistry. Mineralogical studies showed kaolinite and quartz as major mineral phases and lesser amounts of illite, montmorillonite, chlorite, anatase, hematite, and goethite. Mineralogy and positive correlation coefficients of Al, K, Na, and Ca with Cr, U, Th, Ba, Hf, Nb, Rb, V, Sc, Co, Y, Pb, and Ni support the effective role of clay minerals in distribution and concentration of trace elements. The distribution and concentration of lanthanides were controlled by anatase and clay minerals. The rare earth elements (REEs) systematics and ratios like Al2O3/TiO2, TiO2/Zr, Eu/Eu*, (La/Lu)(N), Th/Sc, Th/Co, Th/Cr, La/Co, Cr/Th, and La/Sc indicated that the basaltic igneous rocks within the carbonates of the Ruteh Formation were the potential provenance of the claystones. Geochemical indices such as U, authigenic U, Mn*, Ni/Co, Cu/Zn, U/Th, V/Cr, V/(V+Ni), and Ce/Ce* suggested that the redox conditions of depositional environment of the claystones are mainly oxic. However, chemical index of alteration (CIA; 87-92) and plagioclase index of alteration (PIA; 97-98) suggest intense weathering of the provenance during the deposition of claystones.