148-10 Quantifying Diachroneity of Calcareous Nannofossil Datums at Ocean Drilling Program Hole 1208A, Northwest Pacific

Session: Insights from Microfossils and Their Modern Analogs: From Traditional to Emerging Approaches (Posters)

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Planktic foraminifera and calcareous nannofossils remain the most reliable tools for first-order age control in marine sediments due to their widespread distribution and rapid evolution. The appropriate identification of key species used in biostratigraphy, in addition to reliable age calibrations of first and last occurrences of key datums, is critical for the creation of higher-resolution and more robust age models. These models form the basis for reconstructing past oceanographic conditions and environmental rates of change. One such model is the planktic foraminiferal tropical-subtropical biozonation scheme, which is well-developed with datum events calibrated to the time scale for the Cenozoic. Additional analyses conducted in ocean basins outside of the Atlantic and especially in the mid-latitudes have highlighted that diachroneity of datums is prevalent, indicating the need for more regionally calibrated biostratigraphic zonation schemes. In the Northwest Pacific, one such study documented diachroneity in planktic foraminifera, with ages of datums between that region and the tropical-subtropical scheme differing by several million years in some cases; however, at this location, no previous work has investigated the potential diachroneity of calcareous nannofossil datums. We address this research gap by quantifying the diachroneity of calcareous nannofossil events at Ocean Drilling Program Leg 198 Hole 1208A relative to the geologic time scale 2020 through the Late Neogene. Preliminary findings using updated ages from published nannofossil events at Site 1208A reveal shifts in both first and last occurrences of key nannoplankton species, suggesting regionally diachronous trends. Ongoing work will assess whether these patterns are consistent across holes adjacent to Hole 1208A and explore links to climate events, ecological shifts, or evolutionary dynamics. Future work will investigate nannoplankton diachroneity at ODP Holes 1207A and 1209A in the northwest Pacific and Hole U1506A in the southwest Pacific. 

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7407

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