Stratigraphy and sedimentology of the Middle Jurassic (Callovo-Oxfordian) sequence of Habo Hill, Kutch (Gujarat)

Abstract

The Kutch Basin, a typical pericontinental embayed basin occupying a rifted graben, is filled with a thick Mesozoic succession of rocks which are exposed in the highlands. The study area, located to the northeast of Bhuj, is roughly elliptical in outline with its long axis trending approximately E-W. The Jurassic Sequence of rocks with varied lithologies exposed in the Habo Hill show quaquaversal dips. The older litho-units are disposed in the central region and are surrounded on all sides by younger ones. In all, five lithofacies associations (LFA 1 to 5) have been identified based on the lithological variations which corresponds to the five members of the Habo Formation as designated by Kanjilal (1978) indicating the fluctuating condition of the depositional basin. Two distinct sedimentary sequences are observed: (i) shale and carbonates, and (ii) coarse clastics. The first sequence includes a variety of light to dark coloured shales and limestone. The limestone is generally thin-bedded biomicrite consisting of mud-supported allochemical particles, while the shale is thin to thickly laminated comprised of a varied clay mineral assemblage. The second sequence comprises conglomerate and sandstone The sandstone is relatively well-bedded quartz-arenite with ferrugenous and calcite cements. The stratigraphie variation of field observations, texture and mineralogical characters suggest an early regressive and later transgressive phase of the depositional environment.