Planktonic foraminiferal zonation and sea-level changes in the upper Maastrichtian-middle Danian successions of Meghalaya, India

The biostratigraphic study of the upper Maastrichtian-middle Danian shelf successions of Therriaghat and Mahadeo in Meghalaya, India allowed for the identification of sixty seven species of planktonic foraminifera and recognized the following four zones and eleven subzones: in upperMaastrichtian, Racemiguembelina fructicosa, Pseudoguembelina hariaensis, Pseudoguembelina palpebra and Plummerita hantkeninoides Subzones within the Abathomphalus mayaroensis Zone; in lower-middle Danian Hedbergella holmdelensis and Parvularugoglobigerina longiapertura Subzones within the Guembelitria cretacea Zone, Eoglobigerina fringa and Eoglobigerina praeedita Subzones within the Parvularugoglobigerina eugubina Zone and Parasubbotina pseudobulloides Subzone, Subbotina triloculinoides and Globanomalina compressa Subzones within the uppermost Eoglobigerina edita Zone. The sections are biostratigraphically continuous across the Cretaceous-Paleogene boundary, but the tectonic development of the unstable Therriaghat and Mahadeo blocks caused local tectono-eustatic differences between the two blocks in litho-and biostratigraphy, foraminiferal dispersal, sea-level changes and depositional environments. The succession of the Therriaghat block, where 4 zones and 11 subzoneswere identified, is more complete than the succession of theMahadeo block, which comprises 3 zones and 6 subzones. The ratio of planktonic to benthic foraminifera allowed for the recognition of five transgressive-regressive cycles, most of which have subcycles and pulses. These cycles were calibrated using the planktonic foraminiferal zonation, allowing for detailed documentation of the local history of sea-level change. The extra-basinal tectono-thermal influence, frequent local sea-level changes, suspended clay and microspherules, and greenhouse effect of volcanism caused an increase of temperature and biotic stress in the shelf waters and consequently turnover in the planktonic foraminiferal assemblages, occasional migration and re-appearance, widespread predation, morphological aberrations, dwarfed and anomalous tests, abraded forms andmorphogroups. These paleoenvironmental changesmay have modified the local range of taxa, and the extension of biozones, so that some of the recognized subzones can be local, such as Eoglobigerina fringa and Eoglobigerina praeedita Subzones. Nonetheless, the planktonic foraminiferal assemblages that maintained usual trend of evolution are useful to unravel the complexities of local eustatic history.