5:15 PM - 7:15 PM
[BCG06-P12] Changes in marine Os isotope ratio during the Early Jurassic recorded in bedded chert of the Inuyama area, central Japan
Keywords:bedded chert , Early Jurassic, osmium isotope ratio, Toarcian OAE, Panthalassa ocean
The Early Jurassic is a distinctive period in which significant environmental changes were triggered by the activity of two large igneous provinces (LIPs). The mass extinction at the Triassic-Jurassic boundary is considered to be related to the Central Atlantic Magmatic Province (CAMP), which was emplaced at ca. 200 Ma [1]. Additionally, the Toarcian Ocean Anoxic Event (T-OAE) is also reported to have occurred at ca. 183 Ma, and contemporaneous eruption of the Karoo-Ferrar LIPs could have triggered this event [2]. Osmium (Os) isotope ratio of seawater serves as an effective tool to reconstruct the environmental perturbations associated with such LIP eruptions.
Marine Os isotope ratio is controlled by the relative balance of riverine, hydrothermal, and cosmic dust fluxes that flow into the ocean [3]. Continental crust, which is enriched in radiogenic 187Os, shows high 187Os/188Os ratio, whereas mantle and extraterrestrial materials show relatively low 187Os/188Os ratio. Therefore, Os isotope ratios reconstructed from marine sediments can be used as a powerful proxy for estimating flux changes of continental chemical weathering associated with global warmings [4], and Earth's surface environmental changes caused by volcanic activity with a large eruption of mantle-like materials or gigantic meteorite impacts [5,6].
Several studies have reported increases in marine Os isotope ratios across the T-OAE [7-10]. Based on the observed increase of Os isotope ratio relative to the pre-event value, an increase in continental weathering rate by up to 160 % has been suggested [8]. However, these studies were based on samples deposited in coastal and shallow marine environments of the peri-Tethys and the Panthalassa, which may have not captured the global information. In contrast, bedded cherts deposited in the pelagic Panthalassa are expected to provide a global signal of marine Os isotope ratios.
In this study, we conducted major and trace element analysis, as well as Os isotope ratio analysis, on bedded cherts from the Kurusu section at the Inuyama area, Aichi Prefecture, central Japan, which was deposited during the Late Triassic–Early Jurassic period. The major and trace element analyses were analyzed by XRF and ICP-MS, respectively, and the Re-Os isotope analysis was performed using a multi-collector ICP-MS. In this presentation, we report the analytical results and discuss the variations in the Os isotope ratio during the Early Jurassic, as well as the change of the weathering flux around the T-OAE estimated from the obtained data quantitatively.
[1] Marzoli et al., 1999, Topics in Geobiology 46, 91–125. [2] Pálfy and Smith, 2000, Geology 28, 747-750. [3] Peucker-Ehrenbrink & Ravizza, 2000, Terra Nova, 12, 205–219. [4] Ravizza et al., 2001, Paleoceanography 16, 155–163. [5] Tejada et al., 2009, Geology 37, 855–858. [6] Sato et al., 2013, Nature Communications 4, 2455. [7] Cohen et al.,2004, Geology 32,157–160. [8] Percival et al., 2016, Geology 44, 759–762. [9] Them et al., 2017, Scientific Reports 7, 1–10. [10] Kemp et al., 2020, Geology 48, 976–980.
Marine Os isotope ratio is controlled by the relative balance of riverine, hydrothermal, and cosmic dust fluxes that flow into the ocean [3]. Continental crust, which is enriched in radiogenic 187Os, shows high 187Os/188Os ratio, whereas mantle and extraterrestrial materials show relatively low 187Os/188Os ratio. Therefore, Os isotope ratios reconstructed from marine sediments can be used as a powerful proxy for estimating flux changes of continental chemical weathering associated with global warmings [4], and Earth's surface environmental changes caused by volcanic activity with a large eruption of mantle-like materials or gigantic meteorite impacts [5,6].
Several studies have reported increases in marine Os isotope ratios across the T-OAE [7-10]. Based on the observed increase of Os isotope ratio relative to the pre-event value, an increase in continental weathering rate by up to 160 % has been suggested [8]. However, these studies were based on samples deposited in coastal and shallow marine environments of the peri-Tethys and the Panthalassa, which may have not captured the global information. In contrast, bedded cherts deposited in the pelagic Panthalassa are expected to provide a global signal of marine Os isotope ratios.
In this study, we conducted major and trace element analysis, as well as Os isotope ratio analysis, on bedded cherts from the Kurusu section at the Inuyama area, Aichi Prefecture, central Japan, which was deposited during the Late Triassic–Early Jurassic period. The major and trace element analyses were analyzed by XRF and ICP-MS, respectively, and the Re-Os isotope analysis was performed using a multi-collector ICP-MS. In this presentation, we report the analytical results and discuss the variations in the Os isotope ratio during the Early Jurassic, as well as the change of the weathering flux around the T-OAE estimated from the obtained data quantitatively.
[1] Marzoli et al., 1999, Topics in Geobiology 46, 91–125. [2] Pálfy and Smith, 2000, Geology 28, 747-750. [3] Peucker-Ehrenbrink & Ravizza, 2000, Terra Nova, 12, 205–219. [4] Ravizza et al., 2001, Paleoceanography 16, 155–163. [5] Tejada et al., 2009, Geology 37, 855–858. [6] Sato et al., 2013, Nature Communications 4, 2455. [7] Cohen et al.,2004, Geology 32,157–160. [8] Percival et al., 2016, Geology 44, 759–762. [9] Them et al., 2017, Scientific Reports 7, 1–10. [10] Kemp et al., 2020, Geology 48, 976–980.