Sequence Biostratigraphy: A Case Study from the Godavari Shelf, India

Abstract Quantitative foraminiferal data in a temporal succession identifies a type 1 third order Miocene depositional sequence (Ravva Formation/Sequence) of sechron ~6 Ma in Godavari shelf area. This sequence has developed as a shelf delta build-up. This sequence is divided into a transgressive systems tract (TST) and a highstand systems tract (HST) separated by a maximum flooding surface (MFS), based on faunal frequency trends. The TST plays host to all reservoir facies, suggesting that the sand depocentres have migrated landward, concurrent with progress of the transgressive phase. The Ravva Sequence is bounded below by a type 1 unconformity spanning ~7 Ma across the Oligocene-Miocene boundary. This unconformity surface hosts reservoir facies in well GS-AE-D. The sequence is bounded above by a type 1 unconformity of ~ 10 Ma across the Miocene-Pliocene boundary. This unconformity is a diachronous surface produced by a progradational highstand systems tract. This surface represents possibly the only period during the Neogene, where large quantities of middle to late Miocene sediments may have by-passed the shelf. These by-passed sediments, according to the proposed sequence depositional model, should occur as lowstand systems tract deposits (shelf edge deltas and fan deposits).