Deltaic Sedimentation during Cretaceous Period in the Northern Cauvery Basin, South India: Facies Architecture, Depositional History and Sequence Stratigraphy

The Santonian Campanian sequence of the Cauvery basin was documented with lesser detail owing to its lesser fossiliferous nature and relatively highly fossiliferous bounding stiata. Micro mesoscale lithofacies analysis coupled with documentation of sedimentary and tectonic structures, supplemented by bio and ichnofacies data of the sequence revealed that this sedimentary record represents the development of Gilbert type delta. Various stages of delta development were interpreted to have resulted during a third order glacro eustatic sea level cycle. It is surmised that faulting at the dawn of Santonian that brought down topographic and structural highlands into lows permitted marine transgression and creation of steeply sloping river valley, augmenting intense continental erosion and influx of detrital sediment into the basin. In due course of time, smoothening of valley slope, submergence of river mouth by rising sea level coupled with cessation of detrital influx led to the demise of the deltaic deposition. The information that the bounding surfaces of this Santonian Campanian sequences are recognised to be of sea level lowstands, that led to generation of good reservoir quality in the ensuing depositional products, when coupled with the occurrences of gas and oil pools in the sequence in offshore area of this basin necessitates intense exploration activities. This study has also indicated the presence of three types of variability of reservoir characteristics as defined by three systems tracts.