Absence of Belemnites in the Post-Cenomanian Marine Successions of Cauvery Basin, India: Role of Sea Level, Paleogeography, and Belemnite Paleoecology

Abstract

Belemnites were important Mesozoic marine organisms, and Cretaceous belemnite rostra are found worldwide, including the Cauvery Basin, south-eastern India. However, in the Cauvery Basin, belemnites of the families Belemnopseidae and Dimitobelidae are found only from the Albian-Cenomanian rocks but are absent in the overlying Turonian-Maastrichtian rocks. Although Belemnopseidae became globally extinct in the Cenomanian, Dimitobelidae was still thriving in the nearby Austral regions, so it is not clear why belemnites suddenly suffered local extinction. Moreover, in the post-Cenomanian interval, the newly evolved family Belemnitellidae was thriving globally but is absent in India. To understand the causes of this local extinction as well as the causes of the complete absence in the younger rocks, an analysis of different paleoecological-paleoenvironmental conditions was carried out of all Albian to Maastrichtian formations of the Cauvery Basin against the background of the global belemnite paleobiogeography and evolutionary patterns. The study reveals, during the end Cenomanian, shallowing of the basin caused the local extinction of the shelf-living Belemnopseidae and Dimitobelidae in this basin. In the younger intervals, since India was migrating towards the equator, the stenothermal Dimitobelidae did not survive the warmer water surrounding India and only thieved in the cooler Austral water. Perhaps for the same reason, Dimitobelidae never invaded India, even during the Late Cretaceous transgression. Moreover, during its northern voyage, India was surrounded by deep ocean, acting as a physical barrier for the shelf-dwelling Belemnitellidae of the Boreal Realm to invade India.