Microfacies analysis and depositional environments of the upper Cretaceous (Campanian-Maastrichtian) succession in the Cauvery Basin, southern India

The Cauvery Basin of south India is an ideal reference section for the study of the marine Cretaceous (Aptian-Maastrichtian) sediments. The basin received more than 5500 m thick mixed siliciclastic and calcareous sediments in the course of intermittent phases of marine transgressions/regressions during Aptian-Maastrichtian time. The three microfacies-grainstone, packstone, and wackestone - have been broadly identified in the Campanian-Maastrichtian sediments of the Ariyalur Group of the Cauvery Basin. An attempt has been made here to use the distinctive features of these three microfacies and contained diverse bioclasts for the reconstruction of the physicochemical conditions to unravel the depositional history of this part of the Cauvery Basin, southern India. The facies analysis depicts a shallow marine (maximum depth 10 m) environment with an uninterrupted deepening from the Campanian to Middle Maastrichtian terminating into a basinal conditions during the Late Maastrichtian. The basin was well oxygenated with an average temperature (26 degrees-28 degrees C) of the Cretaceous sea and normal palaeosalinty range (30%-35%). These Campanian - Maastrichtian sediments are deposited on a carbonate ramp setting extending from the inner ramp to the marginal outer ramp.