TY - JOUR
T1 - Redox conditions in the atmosphere and shallow-marine environments during the first Huronian deglaciation
T2 - Insights from Os isotopes and redox-sensitive elements
AU - Goto, Kosuke T.
AU - Sekine, Yasuhito
AU - Suzuki, Katsuhiko
AU - Tajika, Eiichi
AU - Senda, Ryoko
AU - Nozaki, Tatsuo
AU - Tada, Ryuji
AU - Goto, Kazuhisa
AU - Yamamoto, Shinji
AU - Maruoka, Teruyuki
AU - Ohkouchi, Naohiko
AU - Ogawa, Nanako O.
N1 - Funding Information:
The authors thank M. Ikeda, K. Ozaki, T. Nozu, M. Hailstone, A. Pace, H. Yamamoto, and Y. Otsuki for their help and advice during the study. We also thank Chris Reinhard, Simon Poulton, and one anonymous reviewer for their constructive suggestions to our earlier manuscript. This study was partly supported by Grant in Aid from Japan Society for the Promotion of Science (No. 22740352 to Y.S., No. 20109006 and 20340158 to K.S., No. 14403004 and 18340128 to E.T., No. 21840069 to T.N., and No. 21241001 and 18684032 to T.M.).
PY - 2013/8/5
Y1 - 2013/8/5
N2 - The Paleoproterozoic (2.5-2.0 Ga) is one of the most important periods in Earth's history, and was characterized by a rise in atmospheric oxygen levels and repeated (at least three) severe glaciations (the Huronian glaciations). In this study, we investigate redox conditions in the atmosphere and in shallow-marine environments immediately after the first Huronian glaciation based on the isotopic composition of Os, and the abundance of redox-sensitive elements (Os, Re, and Mo) in sedimentary rocks from the Huronian Supergroup, Canada. We found no significant authigenic enrichment of Os in the sedimentary rocks deposited during the first Huronian deglaciation. The initial isotopic composition of Os in the sediments was close to that of chondrite at the time of deposition (Os187/188Os=~0.11). These results suggest that atmospheric O2 levels were insufficient to mobilize radiogenic Os through continental weathering (pO2 < 10 -5-10 -3 present atmospheric level (PAL)). In contrast, we found enrichment of Re in the sedimentary rocks, which suggests the occurrence of oxidative weathering of Re under mildly oxidizing conditions (>10 -8-10 -5 PAL). Despite the Re enrichment, low abundances of Mo imply possible non-sulfidic conditions in shallow-marine environments at the time of deposition. Together with the results of organic carbon and sulfur analyses, we suggest that atmospheric O2 remained at relatively low levels of around 10 -8-10 -5 PAL after the first Huronian deglaciation, which contrasts with proposed dramatic increases in O2 after the second and third Huronian deglaciations. These results imply that the second and third Huronian glaciations may have been global events, associated with climatic jumps from severe glaciations to super-greenhouse conditions and the subsequent blooming of photosynthetic cyanobacteria in the glacial aftermath.
AB - The Paleoproterozoic (2.5-2.0 Ga) is one of the most important periods in Earth's history, and was characterized by a rise in atmospheric oxygen levels and repeated (at least three) severe glaciations (the Huronian glaciations). In this study, we investigate redox conditions in the atmosphere and in shallow-marine environments immediately after the first Huronian glaciation based on the isotopic composition of Os, and the abundance of redox-sensitive elements (Os, Re, and Mo) in sedimentary rocks from the Huronian Supergroup, Canada. We found no significant authigenic enrichment of Os in the sedimentary rocks deposited during the first Huronian deglaciation. The initial isotopic composition of Os in the sediments was close to that of chondrite at the time of deposition (Os187/188Os=~0.11). These results suggest that atmospheric O2 levels were insufficient to mobilize radiogenic Os through continental weathering (pO2 < 10 -5-10 -3 present atmospheric level (PAL)). In contrast, we found enrichment of Re in the sedimentary rocks, which suggests the occurrence of oxidative weathering of Re under mildly oxidizing conditions (>10 -8-10 -5 PAL). Despite the Re enrichment, low abundances of Mo imply possible non-sulfidic conditions in shallow-marine environments at the time of deposition. Together with the results of organic carbon and sulfur analyses, we suggest that atmospheric O2 remained at relatively low levels of around 10 -8-10 -5 PAL after the first Huronian deglaciation, which contrasts with proposed dramatic increases in O2 after the second and third Huronian deglaciations. These results imply that the second and third Huronian glaciations may have been global events, associated with climatic jumps from severe glaciations to super-greenhouse conditions and the subsequent blooming of photosynthetic cyanobacteria in the glacial aftermath.
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U2 - 10.1016/j.epsl.2013.06.018
DO - 10.1016/j.epsl.2013.06.018
M3 - Article
AN - SCOPUS:84882813656
SN - 0012-821X
VL - 376
SP - 145
EP - 154
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
ER -
