Palaeoenvironment and bio-events of the Cretaceous sediments of the Cauvery Basin, India

Abstract

The Cauvery Basin is an important rift margin basin on the east coast of India. Its long research history began in the mid-nineteenth century with the pioneering work of H. F. Blanford. While much of the Cretaceous succession in the basin is fault-controlled, some of the recorded events represent global sea level changes, especially in the mid-Cretaceous. Macrofossils (ammonites, bivalves, etc.) and foraminifera are abundant throughout, and there is an important occurrence of fossil wood and ‘log-grounds’ in the Turonian–Coniacian. The basin is subdivided into a series of sub-basins (known as depressions in earlier literature), which, in places, have their own distinctive depositional history. The results of our collective fieldwork have provided a re-assessment of the lithostratigraphy, biostratigraphy and the tectono-stratigraphical history of the Ariyalur outcrop. Three sedimentary units have been identified: the syn-rift Gondwana Group (of early Cretaceous age), the syn-rift Uttatur Group (of Albian to Coniacian age) and the post-rift Ariyalur Group (of Santonian to Maastrichtian age). Both microfossil and macrofaunal information have been integrated in order to construct a biostratigraphical framework for the basin and develop a tectono-stratigraphical model. Structures exposed onshore, which have occasionally been interpreted as Albian reefs, are thought to be irregularly shaped limestone olistoliths and olistostromes produced by significant intra-Cretaceous faulting and slumping within the basin.