Xing Li , Peter W. Crockford , Yafang Song , Haoming Yin , Wei Wei , Xun Wang , Yuntao Ye , Zhenhua Jing , Fang Huang , Huajian Wang , Jihua Hao
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引用次数: 0
Abstract
Recent studies have revealed the possibility of fluctuations of oxygen in the atmosphere and oceans across the Mesoproterozoic Era. Such fluctuations may have provided the necessary foundation for the emergence and possible early diversification of eukaryotic organisms at this time. However, the current understanding of this apparent coevolution requires further constraints on the operation of the biosphere. Here we analyzed barium isotopic compositions (δ138Ba) together with other geochemical proxies within marine carbonates from the Gaoyuzhuang Formation (∼1570 Ma) of the Yanliao Basin, North China Craton. Our δ138Ba values are similar to those of modern marine pelagic barite, but are lower and less scattered compared to modern seawater δ138Ba compositions. We interpret these new δ138Ba data to reflect the δ138Ba composition of early Mesoproterozoic seawater, at least at the sediment-water interface. Moreover, we do not observe any clear fluctuations in δ138Ba values coincident with carbonate δ13C excursions. We interpret these observations as a response to the accumulation of dissolved barium in the low-sulfate Mesoproterozoic ocean and thus, a buffering of δ138Ba against significant variation in response to local factors such as primary productivity which influence modern marine δ138Ba profiles. Moreover, our calculations estimate a ratio of ≈ 4:1 of continental weathering to hydrothermal activity based on a steady-state box model. Furthermore, our simulations suggest that the residence time of barium was 10–100-fold longer in the early Mesoproterozoic ocean compared to the modern, implying a much more conservative behavior of Ba and its isotopes.
期刊介绍:
Earth and Planetary Science Letters (EPSL) is a leading journal for researchers across the entire Earth and planetary sciences community. It publishes concise, exciting, high-impact articles ("Letters") of broad interest. Its focus is on physical and chemical processes, the evolution and general properties of the Earth and planets - from their deep interiors to their atmospheres. EPSL also includes a Frontiers section, featuring invited high-profile synthesis articles by leading experts on timely topics to bring cutting-edge research to the wider community.