Palaeoenvironmental implications of a turritelline-dominated assemblage from Upper Cretaceous carbonate rocks of Narmada Basin, India

Turritelline-dominated assemblages (TDAs) occur in modern siliciclastic seas within shallow depths, under normal to below normal salinity, high nutrient flux, high ocean upwelling current and/or runoff and cool water conditions. Similar assemblages in carbonate sediments are rare in modern oceans. However, TDA in carbonate rocks are common during the Cretaceous. In this study, we report the presence of a TDA in the late Turonian Nodular Limestone Formation of the Bagh Group, Narmada Basin, central India. An unusually small species of , . Halder, n. sp., is described from the TDA. The TDA, in terms of host rock microfacies and taphonomy, indicates shallow water to intertidal, low to moderate energy, eutrophic to mesotrophic conditions, that prevailed in restricted lagoonal to marginal lagoonal, back-reef environments. The turritellines, based on trace elements and Rare Earth Elements concentration, thrived under dysoxic conditions and experienced above-normal marine salinities. The preferences of modern TDAs do not fully represent such past ecological and lithological conditions, indicating an example of a non-uniformitarian shift in habitat.