High resolution Miocene to Pleistocene calcareous nannofossil biostratigraphy from northeast Indian Ocean: A comprehensive analysis on biohorizons, global correlation, palaeogeography, palaeoecology and sedimentation rate

An in-depth analysis on the calcareous nannofossil content in the Miocene to Pleistocene sediments from the offshore of northeast Indian Ocean has been carried out. The sediments of the NGHP core (NGHP-01-17A) drilled at Andaman-Nicobar Basin are characterized by significant biostratigraphically marker/index taxa of calcareous nannofossils. The calcareous nannofossil biohorizons/zones are assignable to NN9─NN19 zones of Martini (1971) that correspond to CNM13─CNPL7 zones of Backman et al. (2012). The significant calcareous nannofossil bio-events indicate an age from late Miocene i.e., Tortonian (9.81 Ma) to early Pleistocene i.e., Gelasian (1.81 Ma) for the studied samples. The calcareous nannofossil assemblages recorded herein are closely comparable to the assemblages described from other deep sea drilling sites (DSDP, ODP and IODP) located at lower mid latitudes. In the context of palaeoecology, the important and dominant calcareous nannofossils include species of Discoaster, Helicosphaera, Reticulofenestra (small < 3 μm), Reticulofenestra (large > 3 μm) and Sphenolithus, whereas, the subdominant species are Calcidiscus leptoporus and Coccolithus pelagicus. Using the significant calcareous nannofossil biohorizons the sedimentation rate from late Miocene (Tortonian) to early Pleistocene (Gelasian) has been reconstructed. The estimated average sedimentation rates during Tortonian and Messinian are ∼208 m/Ma and ∼64 m/Ma respectively. However, the sedimentation rate during the Pliocene substantially declined. During the Pliocene and Pleistocene (Gelasian) the sedimentation rates have been estimated ∼34 m/Ma and ∼14 m/Ma respectively.