Petrographical and geochemical signatures of Jurassic rocks of Chari Formation,Western India:implications for provenance and tectonic setting

The sandstones of the Ridge and Athleta members of Chari Formation(Callovian-Oxfordian)exposed at Jara have been analyzed for their petrographical and geochemical studies. Texturally, these sandstones are medium to coarse grained, poorly to well sorted, sub-angular to sub-rounded, and show low to medium sphericity.These sandstones were derived from a mixed provenance including granites, granite-gneisses, low and high-grade metamorphic, and some basic rocks of Aravalli range and Nagarparkar massif. The petrofacies analysis reveals that these sandstones belong to the continental block and recycled orogen tectonic regime. The studied sandstones are modified by paleoclimate, distance of transport, and diagenesis. Mineralogically and geochemically, sandstones are classified as quartzarenite, subarkose, arkose, sublithic arenite, and wacke, respectively. The A-CN-K ternary plot and CIA, CIW, PIA, and ICV values suggest that the similar source rocks suffered moderate to high chemical weathering under a hot-humid climate in an acidic environment with higher PCO_2. Generally good to strong correlations between Al_2O3 and other oxides in these sediments indicate clay mineral control. The K_2O/Na_2O versus SiO_2 diagram indicates that the studied samples occupy passive margin fields but the SiO_2/Al_2O_3 versus K_2O/Na_2O plot suggests that the Athleta Sandstone and Ridge Sandstone fall within the passive margin field, while Ridge Shale falls within the active continental margin field.