TY - JOUR
T1 - Triassic marine Os isotope record from a pelagic chert succession, Sakahogi section, Mino Belt, southwest Japan
AU - Nozaki, Tatsuo
AU - Nikaido, Takashi
AU - Onoue, Tetsuji
AU - Takaya, Yutaro
AU - Sato, Keiko
AU - Kimura, Jun Ichi
AU - Chang, Qing
AU - Yamashita, Daisuke
AU - Sato, Honami
AU - Suzuki, Katsuhiko
AU - Kato, Yasuhiro
AU - Matsuoka, Atsushi
N1 - Funding Information:
We are grateful to Ryoko Senda, Hideo Yamamoto and Yukari Otsuki of JAMSTEC and Yayoi Itabashi of the University of Tokyo for their assistance with the Re-Os isotope and ICP-QMS analyses. Constructive comments by two anonymous reviewers much improved our manuscript. This study was supported by the Japan Society for the Promotion of Science through KAKENHI grants JP21840069 to T.N., JP15204048 to Y.K., and JP16H01123 and JP15H02148 to J.-I.K.
PY - 2019/6/15
Y1 - 2019/6/15
N2 - Pelagic cherts preserved in accretionary complexes represent former seafloor sediment that can retain geochemical evidence of paleoceanographic conditions that predate the oldest extant oceanic crust. The ratio of Os isotopes in seawater, in particular, is of wide interest as a source of insight into notable geologic events such as oceanic anoxic events, rapid global warming episodes, and eruption of large igneous provinces, but marine Os isotope records from before 80 Ma are scarce. We present a record of secular variations of marine Os isotope ratios from a thick, continuous succession of Middle and Upper Triassic pelagic chert in the Sakahogi section of the Mino Belt accretionary complex. Initial Os isotope ratios (187Os/188Os) have a wide range in this succession, from 0.197 to 0.813. The variations in this Os record are quite similar to those in the marine Sr isotope record for the same time period, although their amplitudes differ owing to the differing residence times of Os and Sr in the ocean. Together, our results and previous data trace a continuous Os isotope record for ca. 50 Myr starting in Anisian time. We document the following six notable features in the Os record, which also appear in the Sr record, and their interpretation: (1) a negative (unradiogenic) shift associated with euxinia in the latest Anisian reflecting late-stage Siberian Traps eruptions, (2) wide fluctuations from the latest Anisian to Ladinian induced by volcanism and by the late Ladinian humid pulse and volcanism of the Italian Volcanic Center, (3) a continuous decrease in the early Carnian during eruptions of the Wrangellia large igneous province, (4) stable unradiogenic values from the early to early middle Norian associated with a prolonged arid period, (5) a negative spike in the middle Norian associated with the Manicouagan impact event, and (6) a broad rise and fall from the earliest late Norian to the Rhaetian ages, attributed to the Cimmerian-Indosinian orogeny and subsequent volcanism of the Central Atlantic Magmatic Province.
AB - Pelagic cherts preserved in accretionary complexes represent former seafloor sediment that can retain geochemical evidence of paleoceanographic conditions that predate the oldest extant oceanic crust. The ratio of Os isotopes in seawater, in particular, is of wide interest as a source of insight into notable geologic events such as oceanic anoxic events, rapid global warming episodes, and eruption of large igneous provinces, but marine Os isotope records from before 80 Ma are scarce. We present a record of secular variations of marine Os isotope ratios from a thick, continuous succession of Middle and Upper Triassic pelagic chert in the Sakahogi section of the Mino Belt accretionary complex. Initial Os isotope ratios (187Os/188Os) have a wide range in this succession, from 0.197 to 0.813. The variations in this Os record are quite similar to those in the marine Sr isotope record for the same time period, although their amplitudes differ owing to the differing residence times of Os and Sr in the ocean. Together, our results and previous data trace a continuous Os isotope record for ca. 50 Myr starting in Anisian time. We document the following six notable features in the Os record, which also appear in the Sr record, and their interpretation: (1) a negative (unradiogenic) shift associated with euxinia in the latest Anisian reflecting late-stage Siberian Traps eruptions, (2) wide fluctuations from the latest Anisian to Ladinian induced by volcanism and by the late Ladinian humid pulse and volcanism of the Italian Volcanic Center, (3) a continuous decrease in the early Carnian during eruptions of the Wrangellia large igneous province, (4) stable unradiogenic values from the early to early middle Norian associated with a prolonged arid period, (5) a negative spike in the middle Norian associated with the Manicouagan impact event, and (6) a broad rise and fall from the earliest late Norian to the Rhaetian ages, attributed to the Cimmerian-Indosinian orogeny and subsequent volcanism of the Central Atlantic Magmatic Province.
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U2 - 10.1016/j.jaesx.2018.100004
DO - 10.1016/j.jaesx.2018.100004
M3 - Article
AN - SCOPUS:85059780134
SN - 2590-0560
VL - 1
JO - Journal of Asian Earth Sciences: X
JF - Journal of Asian Earth Sciences: X
M1 - 100004
ER -
