Ichnofacies model of a tide‐dominated transgressive topographically controlled embayment system

ABSTRACT Topographically controlled passive embayments can exhibit subtle sedimentological and ichnological differences compared to archetypal estuarine incised‐valley fills. Several restricted‐embayment minibasins developed over the irregular Deccan volcanic topography in the Palaeocene‐Eocene Kutch Basin. In the early Eocene Old Jhulrai minibasin, an integrated sedimentological and ichnological analysis has characterised six depositional subenvironments of a tide‐dominated transgressive embayment. The landward part of the minibasin comprises the facies associations deposited in the tidal channels, supratidal palustrine marshes and intertidal mudflats. The deeper part of the minibasin consists of the facies associations developed within the central bay, along with the backstepping bayhead‐delta parasequences. The trace‐fossil assemblages, as the manifestation of benthic ethology and trophic type in and around the embayment system, define a consequent mosaic of varying brackish‐water marginal‐marine and terrestrial ichnofacies. These are viz ., (1) a stressed Rosselia Ichnofacies in the tidal channel fill; (2) a preservation of Teichichnus Ichnofacies under high salinity fluctuation in the mudflat showing the ‘Crowded Rosselia Ichnofabric’; (3) the Camborygma Ichnofacies in the supratidal inter‐channel palustrine deposit; (4) the stressed Teichichnus Ichnofacies in the bayhead delta front and prodelta deposits, and (5) the completely unbioturbated central‐bay deposits. The bayhead‐delta facies tract exhibits a backstepping stacking pattern separated by the transgressive ravinement surfaces. This retrogradational stacking implies a spasmodically drowned estuarine minibasin during an overall transgressive phase. The early Eocene Old Jhulrai embayment provides a glimpse into its facies tracts and comparison with the Dalrymple‐style archetypal estuarine facies model. Moreover, this topographic embayment, representing an atypical estuarine system, demonstrates the applicability of the novel marginal‐marine ichnofacies (i.e. Rosselia and Teichichnus ichnofacies) albeit with stress‐related modifications.