Physico-chemical tuning of palaeogeographic shifts: Bhuj formation, Kutch, India

The long-standing dilemma between two extremes in palaeogeographic interpretation is resolved for the basal 115 m of the eastern exposures of the Lower Cretaceous Bhuj Formation, at the top of the hydrocarbon prospective Mesozoics of Kutch, India. An explicit record of a mega-scale event of relative sea level rise is found sandwiched between two fluvial stratigraphic intervals that amalgamate only at the eastern extremity of the exposure of the Formation. A localized estuary in the middle had its axis roughly parallel to the pre and post-inundation river channels, although a tributary made a significant detour. Variation in the fine sandstone-mudstone lithology documents decline in depositional energy in the mid-estuary amenable to coal formation. Sediment within the estuary had been routed through both the ends, palaeocurrent turning shore-parallel only at the estuary-mouth. Exception arises in case of some isolated lenses of very poorly sorted and coarse-grained deposits depicting flash floods in the tributary. Burrow characteristics change delicately in response to the inferred changes in the depositional scenario along the estuary.