Stratigraphy and paleobathymetric interpretation of the Cretaceous Karai shale formation of Uttatur Group, TamilNadu, India

The Karai shale Formation of the Uttatur Group is exposed in a bad land area at the western margin of the Cauvery Basin. This shale has been investigated based on foraminiferal fauna and clay minerals. The foraminiferal assemblages obtained contain predominantly calcareous benthic foraminifera, rare planktic and arenaceous foraminifera. The planktic foraminiferal index taxa Planomalina buxtorfi, Rotalipora reicheli, Praeglobotruncana stephani, and Hedbergella portsdownensis suggest the late Albian to middle Turonian age. The benthic assemblage dominated by Lenticulina, Gavelinella, Osangularia and Quadrimorphina, suggests an outer neritic (100–200 m) environment. The clay mineral content dominated by kaolinite-illite-montmorillonite indicates that the Karai shale was formed from weathering of igneous rocks.