Chapter 6 - Subsurface Geology, Depositional History, and Petroleum Systems Along the Western Offshore Basins of India

Abstract

The Western Continental Margin of India (WCMI) unlike the ECMI presents totally contrasting picture. Large onshore basins as well as thick offshore sedimentary depocenters observed along the ECMI are typically absent along the WCMI. The margin consists of four major offshore sedimentary basins such as Kutch, Saurashtra, Mumbai, and Konkan–Kerala (KK) basins separated by transverse basement arches. Further, the eastern Arabian Sea and the adjoining West Coast of India contain several structural features which have evolved mostly as a consequence of rifting and seafloor spreading between India, Madagascar, and Seychelles. The geology of the coastal areas is characterized by the extensive Deccan flood basalts in the north which lie unconformably on the crystalline basement, infilling and blanketing the preexisting Peninsular shield topography. The West Coast south of Deccan basalts is composed almost entirely of Archaean charnockites, gneisses, and granites with limited extents of the Tertiary sediments along the coast of Kerala in the far south. According to Biswas (1982), the dominant structural and tectonic trends along the West Coast, the Dharwar trend (NW–SE to NNW–SSE), the Aravalli trend (NE–SW), and the Satpura trend (ENE–WSW to E–W) have a bearing on the north to south sequential rifting of the Indian Subcontinent during the breakup. The sedimentary basins along the West Coast of India and the adjoining offshore basins can be grouped into two categories: (i) Mesozoic marginal rift basins and (ii) Tertiary offshore rift basins, where Mesozoic prospects are believed to be existing below thick basaltic traps. In this chapter, a brief description of regional geology, subsurface lithostratigraphic history of the offshore sedimentary basins along the WCMI, and the development of petroleum systems of the individual basins is provided. Further, probable Mesozoic prospectivity of the KK offshore basin is also discussed in view of the availability of recently acquired high-resolution seismic data with state-of-art processing techniques which have made the possibility of mapping the sub-basalt sedimentary layers.