MÖssbauer Spectroscopic Study on Characterization of Iron in the Permian to Triassic Deep-Sea Chert from Japan

Abstract

Chemical states of iron in the Permian to Triassic deep-sea chert from Japan have been investigated by 57Fe Mossbauer spectroscopy. In the 57Fe Mossbauer spectra five iron species were identified, that is, hematite (α-Fe2O3), pyrite (FeS2), goethite (α-FeOOH), paramagnetic Fe2+, paramagnetic Fe3+. In the Early to Middle Permian and Middle to Late Triassic cherts, main iron-containing mineral was hematite and less than 35 % of iron was in the ferrous state. This fact suggests that oxic conditions persisted in the deep-sea, such that ferric iron was stable in the sediments. On the other hand, in the Late Permian and Early to early Middle Triassic cherts, main iron-containing mineral was pyrite, and hematite disappeared completely, then more than 65 % of iron was in the ferrous state. This fact suggests that the redox condition of deep-sea open-ocean globally changed from oxic to anoxic for approximately 20 million years across the Permo-Triassic boundary.