Late Pliocene to Early Pleistocene Planktonic Foraminifera from Northern Indian Ocean (Andaman and Nicobar Islands): Interpretation on Cooling Event and Ocean Upwelling

Abstract

Thirty-two planktonic foraminiferal taxa have been identified based on Bright Field microscopic study as well as Scanning Electron Microscopy on the samples collected from the outcrop adjacent to the type section of Neill West Coast Formation at Neil Island of Ritchie's Archipelago, northern Indian Ocean. The planktonic foraminiferal taxa belong to ten genera viz., Dentoglobigerina, Globigerina, Globigerinoides, Globoconella, Globorotalia, Globorotaloides, Globoturborotalita, Neogloboquadrina, Orbulina, and Trilobatus. A number of statistical analyses have been done in addition to taxonomic study to interpret the palaeocenographic scenario. We performed PCA analysis on the foraminiferal content of the samples to test the relatedness. Two biozones have been established by Stratigraphically Constrained Cluster Analysis (CONISS). We used SHEBI (SHE analysis for biozone identification) analysis to precisely demarcate seven biozones. Attempts have been made to decipher the Plio–Pleistocene boundary in the Neill West Coast Formation based on specific zonal markers. The presence of some taxa (e.g., Globoconella inflata, Globigerina bulloides, and Neogloboquadrina pachyderma) indicates the initiation of a cooling event from late Pliocene onwards. An event of ocean upwelling also has been identified based on the presence of Globigerina bulloides, Neogloboquadrina pachyderma, and N. dutertrei from the late Pliocene to early Pleistocene of the northern Indian Ocean that also correlates with palaeoceanographic records known from other upwelling regions.