The Marine Os Isotope Record of the Jemeni-Ethiopean Flood Basalt Eruption

Results from several studies indicate that the eruption of large igneous provinces (LIPs), both continental flood basalts and oceanic plateaus, is associated with shifts toward lower 187Os/188Os ratios in the marine Os isotope record. These isotope excursions are significant because they serve as chemostratigraphic markers of volcanism in the marine sediment record, allowing the environmental consequences of LIP emplacement to be better understood. Here we report bulk sediment Os isotope data from pelagic carbonate sequences from the Indian Ocean (ODP 711), the South Atlantic (DSDP 522), and the Equatorial Pacific (ODP 1218). Previously reported magnetic reversal stratigraphies demonstrate that each of these sediment sequences accumulated during the main phase of the eruption of the Jemeni-Ethiopean Flood basalts (approximately 29-31 Ma; magnetochrons C12n to C10r). All three sites display transient excursions to lower 187Os/188Os during magnetochron C11r. The magnitude and shape of these excursions varies among the sites, between 0.1 and 0.15 in 187Os/188Os, and is very brief, probably less than 200 kyrs in duration. Compared to previously studied LIP events the Os isotope signal associated with emplacement of the Jemeni-Ethiopean Flood basalts is small. Based on a critical assessment of all available data constraining seawater Os isotope shifts coeval with LIP emplacement, oceanic plateau eruptions have a substantially greater influence on the marine Os isotope record than do continental flood basalts.