Characterization of middle Eocene tide-influenced delta: A study from core samples of Hazad Member, Ankleshwar Formation, South Cambay Basin, India

Abstract

The Hazad Member (Middle Eocene) of the Ankleswar Formation in Cambay Basin, India, is traditionally reported as deltaic system. Present work documents three major facies associations, namely, (i) sandstone-rich upper delta plain (FA-1) deposits, (ii) sandstone-mudstone heterolithic lower delta plain–delta front (FA-2) deposits, and (iii) shale-dominated prodelta (FA-3) deposits, in an overall coarsening-up to fining-up succession. Tidalites are well preserved in FA-2 and are represented by laterally accreted tidal bundles, tidal beddings and vertically accreted tidal rhythmites, described from drill core samples in this communication. Laterally accreted tidal bundles with reactivation surfaces in sand-dominated heterolithic units indicate time-velocity asymmetry in subtidal condition. Tidal beddings and tidal rhythmites in mud-dominated heterolithic units, associated with asymmetric/symmetric ripple forms and desiccation cracks, indicate periodic subaerial emergence in intertidal flat depositional setting. Systematic analysis of the architecture of the tidalites in different parts of the basin signifies rapid shift in sedimentation from subtidal to intertidal flat within the lower delta plain. Transitions from prodeltaic to tidally (subtidal-intertidal) affected delta front to lower delta plain and fluvial-dominated upper delta plain depositional systems attest to high frequency transgressive-regressive cycles in response to changing accommodation, as a result of sea level fluctuations and basinal tectonisms in the Cambay Basin.