Evidence for a small ( approximately 0.000 030) but resolvable increase in seawater (super 87) Sr/ (super 86) Sr ratios across the Cretaceous-Tertiary boundary

Previous studies of (super 87) Sr/ (super 86) Sr 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 approximately 0.000 030 in seawater (super 87) Sr/ (super 86) Sr 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 approximately 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 (super 87) Sr/ (super 86) Sr excursion can be explained by enhanced continental weathering, perhaps related to acid rain in the aftermath of the K-T impact.