The marine Os isotope record of the Eocene-Oligocene transition

Osmium isotope analyses of bulk sediment samples from the South Atlantic (DSDP 522), Equatorial Pacific (DSDP 574C) and the Italian Apennines (Massignano) are used to construct a composite record of seawater Os/Os variations across the Eocene-Oligocene (E-O) transition. Between 34 and 34.5 Ma all three records display a pronounced excursion to very low Os/Os (0.29 to 0.26) from higher late Eocene Os/Os ratios (0.4 to 0.45). Following the local minimum Os/Os rises rapidly to approximately 0.6 by 32.5 Ma. Both the late Eocene Os/Os excursion and the asymmetry about this minimum are also apparent LL44-GPC3 record of Pegram and Turekian (1999).