[BCG10-P04] Reconstruction of marine Os-isotope record from upper Aptian to lower Albian to shed light on the relationships between Oceanic Anoxic Event 1b and massive volcanic activities
Keywords:black shale, Cretaceous, OAE1b, Os-isotope ratio
Recently, detailed studies on marine isotopic records of osmium (187Os/188Os) have revealed a direct linkage between massive magmatic episode associated with the emplacement of large igneous provinces (LIPs) and onset of Cretaceous OAEs. For example, Tejada et al. (2009) and Turgeon and Creaser (2008) demonstrated that the onset of the early Aptian OAE1a and end Cenomanian OAE2 were synchronous to the sharp decreases in 187Os/188Os ratio to the typical mantle endmenber. These decreases were interpreted as the increase in the relative supply rate of unradiogenic Os from the LIPs activities. Since the stratigraphic interval representing OAE1b (~113-109 Ma) is close to the ages of the igneous rocks from the Kerguelen Plateau in the Indian Ocean (~120-95 Ma), their causal relationship has also been suggested. However, direct evidence using 187Os/188Os ratio has been lacking so far. In this study, we present marine Os isotopic evolution during the late Aptian and lower Albian to evaluate the impact of massive volcanisms on OAE1b.
We collected pelagic sedimentary rock samples deposited in the Tethys Ocean, from the Poggio le Guaine section, Italy, which is one of the most complete and best-documented OAE1b site (Coccioni et al., 2014). The upper Aptian to lower Albian interval of this section comprises reddish brown to olive argillaceous limestones, marlstones, and mudstones with several cyclically alternating black shales, some of which have been identified as the sedimentary expression of OAE1b. We measured 187Os/188Os ratio and stable carbon isotope ratios of these sedimentary rock samples at Japan Agency for Marine-Earth Science and Technology (JAMSTEC). We will present our recent results.
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