Petrography and geochemistry of Jurassic sandstones, Western Desert, Iraq: implications on provenance and tectonic setting

Abstract

A combined petrographic and geochemical study of the Jurassic Formations, Western Desert of Iraq was carried out to infer their tectonic setting, provenance history, and weathering in the source area. Texturally, these sandstones are immature, poorly sorted, and grain supported. Abundance of feldspars, especially plagioclase indicates rapid deposition of sediments from nearby source rocks. Using the geochemical classification diagram, the Jurassic sandstones are classified mainly as Fe-sand, quartzarenite, and sublitharenite, which is also supported by the petrographic study. The transition trace elements like Co, Ni, Cr, and Cu are lower in the Jurassic sandstones than upper continental crust (UCC) values. Plotting the present data on the provenance discriminating diagrams, most of Hussainiyat and Najmah sandstones fall within felsic (acidic) igneous provenance, and Amij and Muhaiwir sandstones mostly fall in the field of intermediate igneous provenance. The poor correlation between Cr and Ni (r = −0.110, number of samples n = 17) implies that these sandstones were derived from felsic source rocks. Tectonic setting discrimination diagrams based on major elements suggest passive margin and active continental margin. As indicated by chemical index of alteration (CIA) values for the Jurassic sandstones (averages 50 to 65), their source area underwent low to moderate degree of chemical weathering. The petrography and geochemistry results are consistent with a semihumid to semiarid climate for the deposition of these sandstones.