Previous studies of 87Sr/86Sr patterns across the Cretaceous-Tertiary (K-T) boundary have generated inconsistent results. Analyses of samples from Ocean Drilling Program Hole 1049C provide better taphonomic and diagenetic control than has been previously achieved and indicate (1) that there was a rapid increase of ∼0.000 030 in seawater 87Sr/ 86Sr ratios across the K-T boundary, (2) that post–K-T Cretaceous foraminifera at this site are reworked, and (3) that subtle diagenetic overprinting affects the basal ∼15 cm of the Danian ooze. These conclusions are consistent with the asteroid impact hypothesis. Reworking rather than survivorship confirms nearly complete extinction of Cretaceous Tethyan planktic foraminifera; the 87Sr/86Sr excursion can be explained by enhanced continental weathering, perhaps related to acid rain in the aftermath of the K-T impact.

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