It remains unclear whether waning of the volcanic degassing CO2 source or enhancement of the mafic (Ca, Mg-silicate) weathering CO2 sink, or both, caused global cooling leading to the Ordovician greenhouse–icehouse transition. We present a uniquely age-constrained and integrated Middle–Late Ordovician (470–450 Ma) continental weathering isotopic proxy data set (87Sr/86Sr and εNd(t)) from carbonate rocks of the Antelope Range of central Nevada, USA, paired with published paleotemperature proxy measurements (δ18O) of conodont apatite from the same locality. This suite of proxy records signals an increase in mafic weathering of the Taconic mountains (eastern United States) at ca. 463 Ma, which forced a period of global cooling. We adapt a 87Sr/86Sr and pCO2 mass balance approach to model CO2 drawdown during the Ordovician, and show that a combined decrease in volcanic degassing and increase in mafic weathering approximately halves pCO2 in agreement with δ18O trends and paleotemperature reconstructions.

中文翻译：

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Nd同位素证据表明增强的镁铁质风化导致奥陶纪冷却

目前尚不清楚火山脱气 CO2 源的减少或镁铁质（Ca、Mg-硅酸盐）风化 CO2 汇的增强，或两者兼而有之，是否导致全球变冷导致奥陶纪温室-冰室过渡。我们从美国内华达州中部羚羊山脉的碳酸盐岩中展示了一个独特的受年龄限制和综合的中-晚奥陶世 (470-450 Ma) 大陆风化同位素代理数据集 (87Sr/86Sr 和 εNd(t))，并与发表了来自同一地区的牙形石磷灰石的古温度代理测量值（δ18O）。这套代理记录表明，大约在 ca。463 Ma，这迫使全球冷却了一段时间。我们采用 87Sr/86Sr 和 pCO2 质量平衡方法来模拟奥陶纪期间的 CO2 下降，