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Tectonics and Depositional Habitat of Western Offshore Basins, with Special Emphasis from the Mumbai Offshore Basin

Prodyut K. Bhowmick1, Alok Dave1, M. Ayyadurai2, and Pratim Bhaumik1
1ONGC, KDMIPE, Dehradun, India
2ONGC, Western offshore, Mumbai, India

The western continental margin (WCM) basins of India owe their existence to three stages of rift and subsequent drift. The first stage separation of Eastern from Western Gondwanaland during Late Triassic/Jurassic is closely associated with Karoo volcanism in South Africa. The second stage represents the separation of Seychelles-India from Madagascar in Late Cretaceous. The third stage marks the final breakup of Seychelles at Cretaceous/ Tertiary Boundary.

Classically the N-S tectonic elements reported westwards of the Eastern Homocline are the Shelfal-Horst Graben complex, the Kori-Comorin depression, the Kori Ridge, the Laxmi Depression and the Laxmi Ridge (Naini and Talwani, 1982). The recent drilling data has indicated that apart from shelfal horst-graben complex, the remaining grabens have evolved quite late within Cenozoic.Within the shelfal-horst-graben complex, we have synrift sedimentation of Paleocene, ovelying either the Deccan Volcanics or the Precambrian gneissic complex followed by post-rift sediments.

The Kutch basin, the northernmost basin is filled with thick Mesozoic and Cenozoic sedimentary succession genetically related to two major episodes of basin formation.

The Mumbai offshore basin occurring south of Kutch Basin is a rift basin, and is associated with the separation of Seychelles from the Indian sub-continent post-KTB. The main rift represented by the N-S trending Central Graben, is a continuation of the Cambay rift with an offset,and is followed by Vijaydurg graben in south. The intersection of pre-existing E-W Gondwana grabens with the N-S grabens resulted in the formation of major lows, e.g., the Tapti-Daman Low. The genesis of the other major low- the south Bombay low occurring south of Bombay platform is still debatable. Apart from the tectonics imprints developed through the rift, the area is also affected by a number of prominent NE-SW trending strike slip fault which have segmented the basin and resulted in formation of inversion related features in which some of the major hydrocarbons have occurred.

The Kerala-Konkan basin, the southernmost basin of the WCM resulted from the separation of India from Madagascar in earliest Late Cretaceous. The Lower sequence, corresponding to rifting episode and separation of Madagascar from India-Seychelles (earliest part of Late Cretaceous) is identified as Rift sequence. The overlying sediments of Late Cretaceous to Recent represent deposition in Passive margin setup.

Presentation GEO India Expo XXI, Noida, New Delhi, India 2008©AAPG Search and Discovery