GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 76-19
Presentation Time: 9:00 AM-5:30 PM


IKEDA, Masayuki1, HORI, Rie2, OKADA, Yuki2, NAKADA, Ryoichi3 and SAITO, Yu4, (1)Geosciences, Shizuoka University, 836 Ooya, Suruga-ku, Shizuoka, 422-0833, Japan, (2)Department of Earth Sciences, Ehime University, Ehime, 790-8577, (3)Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Kochi Institute for Core Sample Research, Monobe 200, Nankoku, Kochi, 783-8502, (4)Research Institute for Humanity and Nature, Kyoto, 603-8047,

The end-Triassic extinction event (ETE) marks one of the “big five” mass extinction events of the Phanerozoic. The ultimate cause of the extinction is considered to be volcanism of the Central Atlantic magmatic province (CAMP), yet the underlying nature of global environmental changes that accompanied the biotic turnover remains elusive. Here we present chemical and mineralogical studies across the end-Triassic extinction level of the deep-sea chert sequence (Inuyama, Japan). Depleted hematite content normalized by terrigenous material predated the ETE level with significant rock color change from brick red to purple, which is consistent with the rock magnetic records of hematite reported. This suggests the loss of authigenic hematite possibly due to the acidification of bottom-water and the underlying pore-water in sediment. This timing is consistent with the initial eruption of CAMP volcanism, suggesting a catastrophic release of greenhouse gases as a cause of deep-ocean acidification. Across the ETE interval, MgO/Al2O3, Fe2O3/Al2O3, and Al2O3/SiO2 increased with change in color from purple to dusty red. This trend became close to those of weathered CAMP basalts in arid area, implying that it became the considerable source of aeolian dust in cherts after the ETE. These temporal relations support the synchrony among the initial eruption of CAMP, deep-ocean acidification, and the end-Triassic extinction. Similar rock color changes of cherts might have potential information for the volcanisms and deep-ocean acidification in other geologic events. Further isotopic works will constrain their exact timing and quantitative effects across the ETE.