Stratigraphy and Sedimentology of Middle Jurassic Sequence of Chorar Island, Patan District, Kachchh Basin, Gujarat

Abstract

Chorar Island exposes ∼109 m thick middle Jurassic (Bathonian-Callovian) succession in the eastern most part of the Kachchh Basin, Patan District, Gujarat and is divided into two, Khadir and Gadhada formations. It mainly comprises of mixed siliciclastic-carbonate sediments and limestones; the shales dominate the lower part of the succession while the top of the succession is marked by ferruginous sandstone which also forms the vast, prominent peripheral zone of the Chorar dome. The field and laboratory analysis of the succession reveals nine lithofacies which includes ferruginous sandstone, cross bedded white sandstone, micritic sandstone, allochemic sandstone, sandy micrite, mudstone, sandy allochemic limestone, coralline limestone and shale. The mix siliciclastic-carbonate sediments and ferruginous facies are fossiliferous in nature and display sedimentary structures, like ripple marks, cross- and planar-lamination with biogenic sedimentary structures. Coralline limestone facies comprise of large size (>1m diameter) corals, which are diagenetically modified severely and have lost its original internal structures. The sediment characteristics and associated bioclasts indicates low to moderate wave and current energy in shoreface-offshore subsequently changing to wave dominated shoreface during the deposition of the middle Jurassic sediments of the Chorar Island.

Genetic sequence stratigraphy on the basis of ichnology for the Middle Jurassic basin margin succession of Chorar Island (eastern Kachchh Basin, western India)

“…This uplift exposes the basin margin synrift succession of Middle Jurassic age recorded here. The succession in Chorar Island is characterised by distinct and unique facies associations that have recently been described with detailed data on stratigraphy and sedimentology by Patel et al (2018) and on ichnology by Darngawn et al (2018).…”

“…The top of the Hadibhadang Sandstone Member is characterised by coralline limestone which is equivalent to the Raimalro Limestone Member of the Goradongar Formation (Biswas, 2016) and the Patcham Formation of Fürsich et al (2013). The whole succession is capped by the Ratanpur Sandstone Member of the Gadhada Formation (Biswas, 2016;Patel et al, 2018) which consists of thickly bedded, ferruginous sandstone, with cross-bedded white sandstone and thinly bedded mudstone and shales.…”

“…The Middle Jurassic succession ( Fig. 5) of Chorar Island is exposed in discontinuous and isolated patches and comprises a ~109-m-thick succession of the Khadir Formation (Hadibhadang Shale and Hadibhadang Sandstone members) and the Gadha- Our sedimentological analysis has demonstrated nine lithofacies, viz., a ferruginous sandstone, a cross-bedded white sandstone, an allochemic sandstone, mudstone, a coralline limestone, a sandy allochemic limestone, a micritic sandstone, a sandy micrite and a shale facies (Patel et al, 2018). The ferruginous sandstone, cross-bedded white sandstone and micritic sandstone facies are moderately bioturbated, while the sandy allochemic limestone facies is relatively more bioturbated and yields sixteen identifiable ichnogenera (Arenicolites, Asterosoma, Curvolithus, Didymaulichnus, Diplocraterion, Gyrochorte, Halopoa, Hillichnus, Lockeia, Megagrapton, Palaeophycus, Planolites, Protovirgularia, Rhizocorallium, Skolithos and Thalassinoides) (Darngawn et al, 2018), which document a moderate diversity in behaviours (i.e., dwelling, feeding and crawling).…”