Cobalt-based age models of pelagic clay in the South Pacific Gyre

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Dating pelagic clay can be a challenge due to its slow sedimentation rate, post-depositional alteration, and lack of biogenic deposition. Co-based dating techniques have the potential to create age models in pelagic clay under the assumption that the flux of non-detrital Co to the seafloor is spatially and temporally constant, resulting in the non-detrital Co concentrations being inversely proportional to sedimentation rate. We apply a Co-based method to the pelagic clay sequences from Sites U1365, U1366, U1369, and U1370 drilled during Integrated Ocean Drilling Program (IODP) Expedition 329 in the South Pacific Gyre. We distinguished non-detrital Co from detrital Co using multivariate statistical partitioning techniques. We found that the non-detrital flux of Co at Site U1370 is approximately twice as high as that at the other sites, implying that the non-detrital Co flux is not regionally constant. This regional variation reflects the heterogeneous distribution of Co in the water column, as is observed in the present day. We present an improved approach to Co-based age modeling throughout the South Pacific Gyre and determine that the Co-based method can effectively date oxygenated pelagic clay deposited in the distal open ocean, but is less reliable for deposition closer to continents. When extending the method to geologically old sediment, it is important to consider the paleolocation of a given site to ensure these conditions are met.

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Geochemistry, Geophysics, Geosystems