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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Tracking the Hirnantian glaciation using Os isotopes
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Tracking the Hirnantian glaciation using Os isotopes

机译：使用Os同位素追踪Hirnantian冰川

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Here we present initial Os-187/Os-188 (Os-i) values integrated with delta C-13(org) for the first Paleozoic section - the Ordovician/Silurian boundary GSSP at Dob's Linn, Scotland. Our Os-187/Os-188 data tracks major changes in climate that occurred during the Late Ordovician (Hirnantian glaciation), which coincides with the second largest known mass extinction. During the complanatus and early anceps Biozones Os-i values increase from 0.28-1.08. This provides evidence for a period of increased silicate weathering of radiogenic continental crust, likely from the Caledonian Orogen. This increase in weathering was likely the driving mechanism for the drawdown in atmospheric CO2 and global cooling that resulted in the onset of the Hirnantian Glaciation. A decrease to less radiogenic Os-i occurs at the base Hirnantian extraordinarius Biozone and coincides with the trend to more positive delta C-13(org), values that mark the onset of the Hirnantian Glaciation. The trend in Os-i during this interval is ascribed to Hirnantian ice cover and reduced chemical weathering rates cutting the supply of radiogenic material to the Iapetus Ocean. The reduction in silicate weathering enabled atmospheric CO2 to return back to greenhouse levels, causing rapid deglaciation during the mid persculptus Biozone. This period is marked by an abrupt increase in Os-i values from 0.6 to 1.08 over 19 cm of stratigraphy and coincides with the deglacial limb of the delta C-13(org) profile. We interpret the Os-i data to reflect the leaching of exposed radiogenic Os-187/Os-188 bearing glacial deposits and increased weathering of radiogenic Os-187/Os-188 silicate terrane during the deglaciation. Previous workers have identified the Hirnantian glaciation primarily through delta C-13 stratigraphy. However, our Os isotope data indicate that an initial mechanism (i.e. increased silicate weathering) was the driving mechanism behind the Hirnantian Glaciation and subsequent mass extinction. Thus, by coupling Os; and delta C-13(org) proxies we provide the most direct evidence for the initiation and cessation of the Hirnantian glaciation. Furthermore, this study demonstrates the first use of Os-817/Os-188 chemostratigraphy for the Paleozoic as a proxy for reconstructing the Earth's climate system, particularly palaeoceanography.
机译：在这里，我们介绍了第一代古生界-奥陶纪/ Si义界GSSP在多布的林恩，苏格兰的初始Os-187 / Os-188（Os-i）值，其与C-13（org）积分相结合。我们的Os-187 / Os-188数据跟踪了奥陶纪晚期（赫南特冰期）发生的主要气候变化，这与已知的第二大物种灭绝相吻合。在趾骨和足爪早期，生物区的Os-i值从0.28-1.08增加。这提供了可能来自加里东造山带的放射源大陆壳硅酸盐风化增加的时期的证据。风化的增加很可能是导致大气CO2减少和全球冷却的驱动机制，从而导致了赫南特冰川的爆发。辐射降低的Os-i发生在Hirnantian Extraordinarius基本生物区，并且与δC-13（org）呈正值的趋势相吻合，该值标志着Hirnantian冰期的开始。在此间隔期间Os-i的趋势归因于Hirnantian冰盖和化学风化速率的降低，从而减少了向伊阿佩图斯海洋的放射源物质的供应。硅酸盐风化作用的减少使大气中的二氧化碳返回到温室水平，从而在中层百草丛生物区中引起快速的冰消作用。这一时期的特征是，在19厘米的地层上，Os-i值从0.6突然增加到1.08，与三角洲C-13（org）剖面的冰期肢体相吻合。我们解释Os-i数据，以反映冰消融过程中暴露的含放射性Os-187 / Os-188冰川沉积物的浸出和放射性Os-187 / Os-188硅酸盐岩地层的风化增加。先前的工作人员主要通过三角洲C-13地层识别了赫南特冰川。但是，我们的Os同位素数据表明，最初的机制（即，增加的硅酸盐风化作用）是Hirnantian冰川和随后的物种灭绝的驱动机制。因此，通过耦合Os;和delta C-13（org）代理，我们提供了最直接的证据来证明赫南特冰川的形成和停止。此外，这项研究表明，Os-817 / Os-188化学地层学首次用于古生代，作为重建地球气候系统（尤其是古海洋学）的替代物。

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