[BCG08-P01] Marine Osmium isotope record across the Aptian/Albian boundary to elucidate the relationship between the Oceanic Anoxic Event 1b and massive volcanic activities at the Southern Kerguelen Plateau
Keywords:Oceanic Anoxic Event 1b, Osmium isotope ratio, large igneous province
Pelagic sedimentary rock samples were collected from two sites; 1) Poggio le Guaine (PLG) section (Italy) that was deposited in the central-western Tethys Ocean, and 2) Deep Sea Drilling Project (DSDP) Site 463 drilled at the western Mid-Pacific Mountains in the Pacific Ocean. Based on the micropaleontological study on planktonic foraminifera and carbon isotopic analysis of bulk inorganic carbon, the stratigraphy of these two sections was precisely correlated. Indeed, the stratigraphic interval equivalent to the Jacob and Kilian levels were identified for the first time in the Pacific region. Variations of initial 187Os/188Os values were consistent between PLG section and DSDP Site 463 and summarized as follows; 1) relatively stable 187Os/188Os values in the pre-OAE1b interval, 2) decline of 187Os/188Os values at the onset of OAE1b, (3) a first sharp drop of 187Os/188Os at the extinction level, (4) a second sharp drop followed by an abrupt increase in the 187Os/188Os values at the Kilian level, and (5) fluctuation of 187Os/188Os values above the Kilian level. Combining 187Os/188Os data and other geochemical data, we interpreted that the drops of 187Os/188Os values at the extinction and Kilian levels were induced by pulses of hydrothermal activities. Massive volcanic eruptions at the Southern Kerguelen Plateau is one of the most likely candidates to have caused the decreases in isotopic composition of osmium of seawater recorded at PLG section and DSDP Site 463. The close correspondence of osmium spikes to the extinction events within the OAE1b would support a causal link between the volcanic eruptions at the Southern Kerguelen Plateau and the biotic turnover recorded across Aptian/Albian boundary.