The Krishna Godavari Basin is a proven petroliferous basin of continental margin located on the east coast of India. Extensive deltaic plain formed by two large east coast rivers, Krishna and Godavari in the state of Andhra Pradesh and the adjoining areas of Bay of Bengal in which these rivers discharge their water is known as Krishna Godavari Basin. Its onland part covers an area of 15000 sq. km and the offshore part covers an area of 25,000 sq. km up to 1000 m isobath. The basin contains about 5 km thick sediments with several cycles of deposition, ranging in age from Late Carboniferous to Pleistocene.
Krishna Godavari Basin is a Continental passive margin pericratonic basin. The basin came into existence following rifting along eastern continental margin of Indian Craton in early Mesozoic. The down to the basement faults which define the series of horst and grabens cascading down towards the ocean are aligned NE-SW along Precambrian Eastern Ghat trend.
The geological history comprises of following stages:
The basin got initiated through rift / syn-rift tectonics between Permo-Triassic to Early Cretaceous and is essentially characterized by lagoonal to fluvial to occasionally brackish water sediments. The northeastern part of the present onland basin was part of an intra cratonic rift set up till Jurassic that constituted the southeastern extension of NW-SE trending continental rift valley slopping northward. The basin has been initiated through rifting during Permo-Triassic period.
Syn Rift Stage
The early stage synrift sediments were deposited during early subsidence by tectonic fault systems. Basin subsidence continued along basement bound fault system accommodating synrift sediments of late Jurassic to early Cretaceous.
Rift to drift transition is marked by a southerly/ southeasterly tilt of the basin leading to widespread marine transgression during Cretaceous and deposition of marine shale sequence followed by onset of overall regressive phase during Late Cretaceous, represented by a deltaic sequence comprising Tirupati Sandstone with dominant arenaceous facies. During Maastrichtian-Danian, the basin experienced major volcanic activity (Razole Volcanism) covering 1600 sq. km. area and having span of 5.5 million years.
Late Drift Stage
Initial soft collision between the Indian and Eurasian Plates and initiation of Matsyapuri-Palakollu fault appears to have greatly influenced the Paleogene and younger tectonic regiment and the consequent sedimentation pattern.
Sediment induced Neogene tectonics: Increased gradients for the river systems and increased sediment load coupled with significant sea level falls during Neogene had triggered sediment induced tectonics in the shelf and slope parts of the basin creating highly prospective exploration locales. Some of the recent very significant discoveries in these settings had opened new hydrocarbon opportunities in the Krishna-Godavari basin and necessitated re-estimation of its hydrocarbon resource potential.
The five major tectonic elements of the basin are:-
West Godavari Sub Basin
East Godavari Sub Basin