17:15 〜 18:30
[MIS18-P09] Estimation of the duration of Ontong Java Nui volcanism from osmium and carbon isotopic record of the tuffaceous carbonate sequence at the Mid-Pacific Mountains
★Invited Papers
キーワード：オスミウム、白亜紀、シデライト
Lower to mid-Aptian Tethyan sedimentary records are characterized by the repeated deposition of organic-rich sediments (i.g., Selli, Wezel, and Fallot Levels). Recent Os isotopic (187Os/188Os) studies have revealed that these Early to mid-Aptian organic-rich sediments in the Tethyan region are accompanied by the highly unradiogenic 187Os/188Os values (~0.2–0.36), suggesting a massive input of mantle-derived unradiogenic Os. Since radiometric ages of the Ontong Java, Manihiki, Hikurangi Plateaus, which once formed a single large basaltic plateau called Ontong Java Nui (OJN), roughly corresponds to the sedimentary ages of these OAEs, the unradiogenic 187Os/188Os values are interpreted as the strong hydrothermal activity associated with the massive volcanic episode forming the OJN. However, the sedimentary osmium isotopic record does not have the information of where the hydrothermal activity occurred. Furthermore, large uncertainties on the radiogenic and sedimentary ages have hampered the precise chronological correlations between the unradiogenic 187Os/188Os shifts and volcanic activity at the OJN.
DSDP Site 463 is a pelagic carbonate sequence deposited at the Mid-Pacific Mountains, which was once located close to the OJN. The lower Aptian interval of this core consists of siderite bearing limestone and thick tuffaceous sediments which is possibly derived from the volcanic eruption at the OJN. To correlate the tuffaceous interval in DSDP Site 463 derived from the OJN volcanism and the Early to mid-Aptian OAEs in the Tethyan region, we reconstructed the detailed Os and carbon isotopic records of the siderite-bearing carbonate and tuffaceous sequence at the DSDP Site 463 and discussed their linkage.
As the results, the tuffaceous sedimentary interval at the DSDP Site 463 corresponds to the sedimentary interval covering the Selli Level to the Wezel Level in the Tethyan region which supports the hypothesis that volcanic eruptions at the OJN are the triggering factor of these OAEs. Also, the siderite bearing interval corresponds to the sedimentary interval of the Selli, Wezel, and the Fallot Levels. Given the siderite is formed under the reducing, high dissolved inorganic carbon content, and iron-rich porewater condition, the distribution of the siderite suggests that reducing and ferruginous pore-water condition was sustained until mid-Aptian after the main volcanic pulse of OJN.
DSDP Site 463 is a pelagic carbonate sequence deposited at the Mid-Pacific Mountains, which was once located close to the OJN. The lower Aptian interval of this core consists of siderite bearing limestone and thick tuffaceous sediments which is possibly derived from the volcanic eruption at the OJN. To correlate the tuffaceous interval in DSDP Site 463 derived from the OJN volcanism and the Early to mid-Aptian OAEs in the Tethyan region, we reconstructed the detailed Os and carbon isotopic records of the siderite-bearing carbonate and tuffaceous sequence at the DSDP Site 463 and discussed their linkage.
As the results, the tuffaceous sedimentary interval at the DSDP Site 463 corresponds to the sedimentary interval covering the Selli Level to the Wezel Level in the Tethyan region which supports the hypothesis that volcanic eruptions at the OJN are the triggering factor of these OAEs. Also, the siderite bearing interval corresponds to the sedimentary interval of the Selli, Wezel, and the Fallot Levels. Given the siderite is formed under the reducing, high dissolved inorganic carbon content, and iron-rich porewater condition, the distribution of the siderite suggests that reducing and ferruginous pore-water condition was sustained until mid-Aptian after the main volcanic pulse of OJN.