The influence of extraterrestrial material on the late Eocene marine Os isotope record

A reconstruction of seawater Os-187/Os-188 ratios during the late Eocene (similar to 36-34 Ma), based upon bulk sediment analyses from the sub-Antarctic Southern Atlantic Ocean (Ocean Drilling Program (ODP) Site 1090), Eastern Equatorial Pacific Ocean (ODP Sites 1218 and 1219) and the uplifted (land-based) Tethyan section (Massignano, Italy), confirms that the previously reported abrupt shift to lower Os-187/Os-188 is a unique global feature of the marine Os isotope record that occurs in magnetochron C16n.1n. This feature is interpreted to represent the change in seawater Os-187/Os-188 caused by the Popigai impact event. Higher in the Massignano section, two other iridium anomalies previously proposed to represent additional impact events do not show a comparable excursion to low Os-187/Os-188, suggesting that these horizons do not record multiple large impacts. Comparison of records from three different ocean basins indicates that seawater Os-187/Os-188 begins to decline in advance of the Popigai impact event. At Massignano this decline coincides with a previously reported episode of elevated He-3 flux, suggesting that increased influx of interplanetary dust particles (IDPs) contributed to the pre-impact shift in Os-187/Os-188 and not to the longer-term latest Eocene Os-187/Os-188 decline that occurred similar to 1 million year after the Popigai impact event. Published by Elsevier Ltd.