Textural and petrographic characterization and implication of diagenesis in the interpretation of provenance and depositional environment of the sandstones of the Middle Jurassic Jumara formation, Kachchh mainland, Gujarat

Abstract

The sedimentary basin of Kutch in Gujarat, Western India is known for extensive development of the Jurassic sequence. The excellent Jurassic outcrops of Kutch have attracted the attention of many stratigraphers, paleontologists and sedimentologists over more than a century. Lithologically, the exposed Jurassic succession is divided into three formations viz., the Jhurio, the Jumara and the Jhuran formations. The Lower, Jhurio Formation is represented by a predominant carbonate facies inter-bedded with clastics, the Middle, Jumara Formation is mainly a carbonate - siliciclastic succession and the upper, Jhuran Formation is mainly a fine-grained siliciclastic sequence. In the present paper, the textural, petrographic and diagenetic character of the sandstones observed from various horizons has been utilized for the interpretation of provenance and palaeoenvironment of the sequence. The textural parameters suggest a fluctuating near shore beach to shallow marine environment of deposition. Petrographicaily the sandstones belong predominantly to Quartz and feldspathic arenite categories followed by subordinate sub-litharenite category and fall into the recycled orogenic setting field of tectonic provenance diagram. Compaction, cementation (silica and calcite cements), hematite pigmentation, clay mineral authigenesis are the important diagentic changes observed in these sandstones. The present study on the mineralogical composition arid provenance of sandstone in association with textural characteristics suggest their derivation from a recycled crystalline igneous and metamorphic source possibly from north and east.