Petrography and Diagenesis of the Jurassic Jara Dome sandstones, Kachchh, Gujarat

Abstract

The sandstones of Ridge and Athleta members of Callovian and Oxfordian age exposed at Jara Kachchh, Gujarat have been studied for their petrography and diagenetic history. These sandstones are medium– to coarse–grained, moderately to well sorted, subangular to subrounded and show medium to low spherecity. These sandstones were derived from a mixed provenance including granites, granite–gneisses, low–and high grade metamorphic and some basic rocks of the Aravalli Range and Nagarparkar Massif. A critical analysis of the various factors that have modified the original detrital composition of Ridge and Athleta sandstones indicates that tropical weathering under warm and humid conditions and long residence time at the sediment water interface in a shallow marine environment destroyed the labile grains and enriched the sandstones in quartz. The dominance of floating grains and point contacts in the sandstones indicate that detrital grains do not show much pressure affects is a result of either shallow burial or early cementation. The sandstones were cemented by iron oxide, carbonate, silica, dolomite, glauconite and clay in order of abundance at a depth of burial in the range of 670–2600 m and 762–2750 m.