Middle to Late Miocene Integrated Biostratigraphy and Biozonation for the Mid-Latitude Indian Ocean (odp Site 752)

The Middle to Late Miocene represents a critical time interval in the Indian Ocean (IO), due to the establishment of a near-modern monsoonal wind system and a reorganization of land masses, as well as significant climatic changes following the Middle Miocene Climatic Transition and the subsequent northward shift of the Westerlies during the Late Miocene. However, the response of the intermediate and surface ocean dynamics to these forcing mechanisms in the southeastern IO remains poorly understood. In this regard, Ocean Drilling Program (ODP) Site 752, located on the western flank of Broken Ridge (30° 53.475ˈS/93° 34.652ˈE), represents a key location to understand the relation of the oceanic currents and the above-mentioned mechanisms in the eastern sector of the IO during the studied Miocene interval. An initial biostratigraphic framework for ODP Site 752 was established during ODP Leg 121. However, only a low-resolution age-depth model was attained during the shipboard analyses for the Middle to Late Miocene. In this respect, we present a newly updated high-resolution biostratigraphic age-depth model based on fully quantitative nannofossil assemblage analyses and planktonic foraminifera datums for the time interval between ~8 – 15 Ma at Hole 752A. The biostratigraphic age-depth model was compared with a recently published astrochronologically tuned age-depth model (Lyu et al., 2023; DOI: 10.1029/2023PA004761) for further validation. The comparison between models revealed an overall high consistency, except for the interval between ~12 – 13 Ma, where the age difference is high. We link these discrepancies to potential age differences in the recorded bioevents for this interval between basins, as well as to the error associated with the mathematical approach of the tuned age model. This approach led to the development of a new regional biozonation scheme for both fossil groups in the southeastern IO. The ages provided by the astronomically tuned age-depth model for the recorded biostratigraphic events were compared against already available data to ascertain the evolutionary patterns of calcareous nannofossils and planktonic foraminifera across the Middle to Late Miocene. Our results revealed that both Discoaster kugleriand Globoturborotalita nepenthes appeared earlier in the southeastern IO than in the equatorial latitudes, demonstrating a strong latitudinal influence in the evolutionary pattern of these two species. Additionally, our data showed that the Top of Globoconella panda, an IO specific event commonly placed at 11.93 Ma, occurred at 10.54 Ma at Site 752. Thus, we conclude that the Top G. panda constitutes an unreliable marker in the region and that further revision is needed to constrain the occurrence of this event in the IO.