Post-Cretaceous record of larger foraminifera from the Shillong Plateau, India: an evidence of environmental recovery during Early Cenozoic

Abstract

The Late and post-Cretaceous succession of larger benthic foraminifera and planktic microfossils from the Shillong Plateau indicates events of extinction and recovery of the biotic forms. These events are interpreted using a conceptual framework involving biological responses to environmental changes caused by eustatic and climatic variations. Stratigraphic distribution shows that the Late Maastrichtian larger benthic foraminiferal assemblage disappears earlier than the planktic microfossils at the boundary interval. After their last occurrence in the Upper Maastrichtian, the larger foraminifera reappears in the carbonates of the Lakadong Formation dated by Glomalveolina primaeva as the Thanetian (P4).

The event of the first appearance of larger foraminifera in the Shillong Plateau correlates with zone P4. When compared with other Tethyan sections (e.g., Mediterranean) where they start occurring in the strata equivalent to zone P3b, the event of their reappearance appears to be slightly delayed in the studied section. The P3b zone is the interval marked by the onsetting of habitable conditions on shelves (oligotrophic environments) and is followed by an interval (the equivalent of the P4 zone) of extensive carbonate generation, during which highly diversified larger foraminiferal assemblages evolve and become widely distributed. The Shillong assemblage, therefore, marks the phase of "expanded oligotrophy" in which recovery of carbonate platform environments occurred on a large scale on shallow neritic shelves.