期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2012
卷号：109
期号：45
页码：18300-18305
DOI：10.1073/pnas.1120387109
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Carbonates from approximately 2.3-2.1 billion years ago show markedly positive {delta}13C values commonly reaching and sometimes exceeding +10{per thousand}. Traditional interpretation of these positive {delta}13C values favors greatly enhanced organic carbon burial on a global scale, although other researchers have invoked widespread methanogenesis within the sediments. To resolve between these competing models and, more generally, among the mechanisms behind Earth's most dramatic carbon isotope event, we obtained coupled stable isotope data for carbonate carbon and carbonate-associated sulfate (CAS). CAS from the Lomagundi interval shows a narrow range of {delta}34S values and concentrations much like those of Phanerozoic and modern marine carbonate rocks. The {delta}34S values are a close match to those of coeval sulfate evaporites and likely reflect seawater composition. These observations are inconsistent with the idea of diagenetic carbonate formation in the methanic zone. Toward the end of the carbon isotope excursion there is an increase in the {delta}34S values of CAS. We propose that these trends in C and S isotope values track the isotopic evolution of seawater sulfate and reflect an increase in pyrite burial and a crash in the marine sulfate reservoir during ocean deoxygenation in the waning stages of the positive carbon isotope excursion.
关键词：Lomagundi excursion ; Great Oxidation Event ; Precambrian
