ABSTRACT: Precambrian Trends, Continental Breakup and Giant Oil Fields in India

GOMBOS, A. M., Jr., W. G. POWELL, and I. O. NORTON, Exxon Production Research Co., Houston, TX

Two giant oil fields (Ankleswar and Bombay High) have been discovered in the coastal basins of India. Although 12 rift-related sedimentary basins occupy the Indian continental margins, the giant fields are restricted to basins in northwestern India by a unique convergence of tectonic events. Mesozoic rifting along structural trends of Proterozoic mobile belts formed the passive margin basins of the Indian coasts; most of these basins resulted from simple extensional episodes. During Campanian rifting of Madagascar from India, north-south-striking normal faults propagated into Cambay Graben. Late Maastrichtian doming over the incipient Reunion hotspot imparted extensional stresses to the northwestern Indian coast and formed the fault-block that became the Bombay High. After eruption of Deccan flood basalts in early Paleocene, extension continued in the weakened crust. This resulted in enhanced subsidence of Cambay Graben and Surat Depression, rifting of Seychelles microcontinent from India, and reactivation of normal faults on the emergent Bombay High. Cambay Graben and Surat Depression filled with Tertiary organic-rich source shales as they underwent thermal subsidence. Shallow water Tertiary carbonates developed on the slowly subsiding Bombay Platform; sea-level oscillations fostered secondary porosity development. Late Tertiary maturation of source shales generated hydrocarbons that migrated into carbonate reservoirs on Bombay High. Ankleswar field is related to a poorly understood Pliocene or Pleistocene transpressional event that deformed Tertiary clastics into an iclines that filled with hydrocarbons from the Surat Depression. Konkan-Kerala basin and the older basins of the east coast were unaffected by the post-Campanian tectonic events and therefore lack the favorable play elements that characterize the giant fields.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)