The Krishna Godavari Basin is a passive margin basin comprising of a number of North East – South West trending horsts and grabens. Tectonically, the basin can be divided into three sub basins , namely the Krishna, West Godavari and East Godavari Sub Basins which are seperated by the Bapatla and Tanuku Horsts respectively. The West Godavari Sub Basin is further separated by Kaza – Kaikalur Horst into the Bantumilli and Gudivada Grabens (Fig 1). The onland part of East Godavari sub basin has been further differentiated into the Mandapeta Sub Basin on the West and Narsapur Sub Basin on the East by the Yanam Ridge. The offshore part of the East Godavari Sub Basin is the Godavari Offshore Sub Basin. The depositional environment of Krishna – Godavari Basin is controlled by a series of rifting phases. The early- rift phase in the Permo – Triassic produced a fluvial and brackish water environment. The main rift phase during the early Cretaceous resulted in deltaic to fluvial conditions prevailing in the area. The initiation of main rift phase in the middle Jurassic resulted in the formation of a North East – South West trending West Godavari sub- basin which was filled with synrift sediments. Continued tectonism at the end of theJurassic resulted in the formation of the Kaza high, a central horst which bisects the West Godavari sub basin. The Early Cretaceous period saw continued continental dominated deposition, although marginal marine conditions became increasingly common, with open marine incursions evident towards the end of the rift phase (Barremian age). The end of rifting and onset of thermal subsidence is marked by an erosional unconformity followed by a basin wide flooding and blanketing of synrift sediments by the marine Raghavapuram shale….
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