The osmium isotopic composition change of Cenozoic sea water as inferred from a deep-sea core corrected for meteoritic contributions

A detailed study was made of the oceanic Os-187/Os-186 variation through th e Cenozoic by using a hydrogen peroxide leaching procedure on a pelagic cla y core from the North Pacific (Long Lines-44 GPC3). A 6% H2O2 solution was used. The range of Os-187/Os-186 obtained by this procedure was between 2 a nd 8.2. A milder leach (0.15% H2O2) in three out of four samples yielded a slightly higher Os-187/Os-186 value than the stronger leach implying that t he stronger leach released some meteoritic Os with Os-187/Os-186 of 1. Usin g published He-3 concentrations in GPC3 and cosmic dust He-3 and Os fluxes to deep-sea sediments, the extraterrestrial Os concentration was estimated for each core segment;and subtracted to yield "corrected" values of Os-187/ Os-186. The results based on the milder leaching protocol and the He-3 corr ection protocol yield similar values. The "corrected" ocean water Os-187/Os -186 pattern for the past 25 million years is similar to that obtained by o ther workers and is compatible with other results for the entire Cenozoic. The variation with time in GPC3, uniquely, provides a statigraphic signatur e for the Paleogene. Copyright (C) 1999 Elsevier Science Ltd.