Provenance, tectonic setting, and source area weathering of Middle Jurassic siliciclastic rocks of Chari Formation, Jumara Dome, Kachchh Basin, Western India: Sedimentological, mineralogical, and geochemical constraints

Abstract

Kachchh Basin is well known for its Jurassic sediments and hydrocarbon prospects, but geochemically, these sediments remained less explored. Here, we present petrography, mineralogy, and geochemistry of the Middle Jurassic sandstone and shale of the Chari Formation exposed at Jumara Dome, Kachchh Basin, to understand their provenance, tectonic setting, source area weathering, and paleoclimate. Petrographic analysis shows that the sandstone consists of abundant quartz, feldspar (K‐feldspar and plagioclase), mica (muscovite and biotite), and lithic fragments. The X‐ray diffraction analysis of both sandstone and shale reveals the presence of abundant quartz, and lesser amount of kaolinite, illite, and chlorite. The presence of these clay minerals was also attested by scanning electron microscope analysis. Based on framework composition and geochemistry, the sandstone is classified as arkose to subarkose and shale as graywackes. Detrital modes and geochemical data suggest the derivation of these clastic rocks from a felsic source, partially influenced by sediment recycling and deposited in a passive margin setting in a rifted basin. Values of weathering indices including chemical index of alteration, plagioclase index of alteration, chemical index of weathering, and index of compositional variability indicate that the rocks of Jumara Dome are mature and the source area has undergone a moderate to high degree of chemical weathering under warm and humid climatic conditions. The petrography, bulk mineralogy, scanning electron microscope analysis, and geochemical composition in conjunction with paleocurrent data affirm the supply of detritus for Jumara Dome from the Aravalli Craton situated to the east and northeast and Nagar Parkar Massif situated to the north and northwest of the basin. This study endorses the formation of Transgondwanan seaway route during the Late Oxfordian, which caused a marine transgression onto the land.