A High-Resolution Marine 187 OS / 188 OS Record for the Late Maastrichtian

Abstract

The marine osmium (Os) isotope record can potentially act as an independent proxy indicator of major volcanic activity, marked by decreases in seawater 187Os/188Os to more mantle-like values. A composite late Maastrichtian (66 to 68.5 Ma) marine Os record, based on bulk sediment samples from the Southern Ocean (Ocean Drilling Program (ODP) Site 690), the Tropical Pacific Ocean (Deep Sea Drilling Project (DSDP) Site 577), the South Atlantic (DSDP Site 525) and the paleo-Tethys Ocean, provides robust evidence of a 20% decline in seawater 187Os/188Os over a period of about 200 ka early in magnetochron C29r, ending approximately 200 ka before the Cretaceous-Paleogene (K-Pg) boundary (Robinson et al., 2009). This shift in 187Os/188Os is interpreted as a chemostratigraphic marker of Deccan volcanism, and is temporally separate from the Os isotope excursion associated with the Chicxulub impact at the K-Pg boundary. Improved geochronologic data constraining the eruptive history of the Deccan (Renne et al., 2015; Schoene et al., 2015), as well as Os isotope records coinciding with other episodes of large igneous province (LIP) eruption (Duvivier et al., 2015; Bottini et al., 2012; Kuroda et al., 2010), provide a new and larger context for understanding the response of the marine Os record to LIP emplacement. Comparison of Os isotope records coinciding with other LIP events to the Deccan/K-Pg record reveal important differences in the structure and duration of shifts in the Os isotope record, and precludes a single interpretation of all LIP-associated Os isotope excursions.