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Triassic-Jurassic boundary(TJB) is one of the Big Five extinction events through the Phanerozoic, and a number of investigations have revealed a carbon-isotopic excursion across the boundary in shallow, continental shelf sediments. However, shallow sea sediments such as shale, mudstone and platform carbonate are not free from the influence of local geology and environment. So their carbon isotopic excursions may not represent global signature but local or regional anomalies. Pelagic deep-sea sediments such as bedded chert are more reliable as a global paleo-enviromental indicator. Furthermore the comparison between shallow and deep-sea sediments is expected to provide information of oceanic structure during the TJB event. However, content of organic matters in deep-sea chert is extremely low, generally less than 0.05%. We analyzed organic carbon content and carbon-isotopic values of radiolarian bedded chert from the continuous section of Inuyama area, SW Japan. The section consisted of alternating radiolarian chert layers (0.5 to 15cm in thickness)and shale layers (1 to 10mm in thickness). They were identified as low altitude pelagic deep-sea sediments of Panthalassa based on paleomagnetic and stratigraphic investigations. Intensive marine microfossil studies revealed a rapid radiolarian faunal change from Triassic type to Jurassic type and disappearance of conodonts at TJB. Study samples were mostly selected from radiolarian chert layers because they are not suffered from weathering comparing with the shale. Condensation and extraction of organic carbon was conducted in the following procedures. At first, carbonate minerals were removed with 1.5N hydrochloric acid, then the residues were treated by 48% hydrofluoric acid to remove silicates after acidification by 4N hydrochloric acid to prevent formation of fluorides. Finally the residual solids were soaked with 4N hydrochloric acid. The treated residues in each step were washed with distilled water sufficiently. As a result, about 30 to 35g of sample powder became 0.05 to 0.22g. These condensed samples included 1.7 to 9.2% carbon, so their initial values are thought to be less than 0.02%. The carbon isotope values are approximately -29 to -26‰. The record shows a depleted values, -29‰ during the late Triassic, then it marks about -26‰ with about -2‰ positive excursion just above the TJB of conodonts disappearing horizon. The values return to the level about -29‰ at early Jurassic. The positive excursion is possibly correlated with reports from Canada (Williford et al.,2007) and USA (Ward et al.,2006). Proxies from pelagic deep-sea sediments are considered to indicate global environmental change at that age. So the positive excursion of organic carbon-isotope just above TJB is probably global characteristic feature. Timing and duration of the positive excursions will be discussed between the shallow and deep-sea environments in terms of the reconstruction of the environmental change at the TJB.
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