Abstract

We present a reference curve of seawater 87Sr/86Sr variation through the past 7 m.y. based on 455 samples of planktonic foraminifera from Ocean Drilling Program (ODP) Site 758 in the Indian Ocean. This single-site curve is superior to extant curves because of several features: (1) a continuous sedimentary section free of disturbances; (2) a well-determined and precise chronostratigraphy that is calibrated to numeric age on the basis of continuous magnetostratigraphy and a refined astronomical time scale; (3) a high temporal resolution (sample interval averages 15 ka); (4) an improved analytical reproducibility; and (5) a uniformly high sample quality. The gross structure of the Site 758 curve is generally similar to that observed in previous work, but the increased temporal resolution and decreased analytical scatter of the curve provide improved chronostratigraphic resolution. At the 95% confidence level, uncertainties on age estimates range from ±0.60 m.y. in the lower Pleistocene and upper Miocene to ±2.03 m.y. in the middle Pliocene. Moreover, this detailed record identifies two periods of steplike increases in seawater 87Sr/86Sr (6.10 to 5.80 Ma and 1.46 to 1.13 Ma) that are characterized by rates of change of ∼150 × 10−6/m.y. These features, if verified at other sites, indicate abrupt changes in the Sr mass balance of the ocean and may be used as precise event markers in late Neogene marine sections.

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