Strontium and rubidium concentrations of ODP Site 104-642 (Table 1)

We have attempted to date several samples from Site 642 using a combination of Sr isotope stratigraphy and Rb-Sr dating of glauconite. A carbonate shell fragment from Sample 104-642B-22H-6, 70-73 cm gives a Sr isotope stratigraphy date of 17.3 +/- 1.0 Ma, which agrees well with available biostratigraphic and paleomagnetic data. Glauconites from a nearby sample (104-642B-23H-1, 66-69 cm) give a similar date.
One carbonate shell fragment and two fish teeth samples from Core 104-642D-12X give concordant Sr isotope stratigraphy ages of about 37 Ma (latest Eocene). Rb-Sr glauconite analyses from one of the samples, while showing some substrate contamination, also support an Eocene age. Our results are in conflict with Miocene palynomorph dates from Core 104-642D-12X. As specific reworking of fish teeth and carbonate macrofossils (and also glauconite) from 37 Ma old sediments into three different samples in Core 104-642D-12X is most unlikely, we view the 37-Ma date as the depositional age of the core.