Sedimentology of Limestones in Niniyur Formation, Paleocene, Cauvery Basin, South India

Niniyur Formation, composed essentially of limestones, of Paleocene age, is exposed along a narrow stretch in the Ariyalur outcrop area. The maximum exposed thickness of 15 m constitutes but a part of the Formation, the rest being concealed by the Cuddalore Sandstone. Three shallow boreholes ENE of Sendurai and 2 stratigraphic information wells in Tanjore area indicate that the Formation extends subsurface over a large area.

Exposed sections show sandy and clayey limestone of wackestone texture, deposited in shelf lagoon environments. But eastward in the subsurface, the formation becomes pure limestone (algal lime boundstone-packstone-grainstone) deposited in algal banks. In the Tanjore area the formation is composed of foraminiferal and algal lime packstone-wackestone, probably deposited in quiet to slightly agitated inner to middle shelf environments. In the deeper parts of the basin, under favourable conditions of tectonics and clastics dispersal, transgressive carbonates of similar age and lithology could be expected.