Abstract

The late Jurassic to early Cretaceous rifting between India/Australia and India/Antarctica resulted in the formation of a number of NE–SW-trending basins in the Indian Precambrian crystalline basement. The Cauvery Basin is the southernmost basin along the eastern margin of the Indian Sub-Continent, covering much of this part of India and extending a considerable distance offshore. The basin comprises several ‘depressions’, or sub-basins, with the Ariyalur–Pondicherry Depression in the north. The exposed successions are in the southern part of this sub-basin.

The result of fieldwork (1994–8) has been a reassessment of the lithostratigraphy and the tectonostratigraphic history of the Ariyalur outcrop. Three major sedimentary groups were identified: the syn-rift Gondwana Group (of early Cretaceous age), the syn-rift Uttatur Group (of Albian to Coniacian age) and the post-rift Ariyalur Group (of Santonian to Maastrichtian age). Both microfaunal and macrofaunal information were used to develop a biostratigraphic framework for the basin and a new tectonostratigraphic model. This new model for the development of the basin is significantly different to that used by the Oil and Natural Gas Commission of India. Structures exposed onshore, which have been interpreted as Albian reefs, are interpreted here as irregularly shaped limestone olistoliths/olistostromes produced by intra-Cretaceous rifting and slumping within the basin. The paper discusses this model for the basin history which is calibrated by updated foraminiferal (and macrofossil) biostratigraphy.

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