Role of seafloor production versus continental basalt weathering inMiddle to Late Ordovician seawater 87Sr/86Sr and climate
Role of seafloor production versus continental basalt weathering inMiddle to Late Ordovician seawater 87Sr/86Sr and climate
复制标题
DOI：
10.1016/j.epsl.2022.117641
复制
发表时间：
2022-09-01
影响因子：
5.3
通讯作者：
Olesik, John W.
中科院分区：
文献类型：
--
作者：
Avila, Teresa D.;Saltzman, Matthew R.;Olesik, John W.
奥陶纪（486.9 ~ 443.1 Ma）的全球气候以降温为特征，并在希尔南天冰期达到顶峰。含钙和含镁硅酸盐矿物的化学风化作用以及随后在海洋碳酸盐中捕获的碳在数百万年的时间尺度上充当了大气二氧化碳的汇，玄武岩比花岗岩成分的岩石消耗二氧化碳的速度更快。海洋Sr同位素比值（Sr-87/Sr-86）可作为玄武岩与花岗岩风化相对比例的地球化学指标。氧同位素（δ O-18）作为古温度和冰体积的代表，在古气候研究中为Sr-87/Sr-86提供了有益的补充。以前的研究报告了在中奥陶纪至晚奥陶纪的逐渐冷却（δ O-18增加）。结合Sr和C旋回模型，提出了大陆基性物质的硅酸盐风化作用驱动奥陶系降温的假说（如Taconic造山运动）。然而，Sr和C旋回模型没有考虑到中奥陶世（Darriwilian）海平面和海底生产的明显上升，这将增加热液Sr通量以及沿大陆火山弧的脱气。此外，一些奥陶纪研究如果不是基于配对分析，则Sr-87/Sr-86和δ O-18曲线之间存在时间上的不确定性，这可能会模糊硅酸盐风化和冷却之间的关系。在此，我们提出了来自牙形石磷灰石的新的配对Sr-87/Sr-86和δ O-18数据，并将其与确定性（正）和随机（反向）建模方法相结合，认为热液风化作用的增加在推动海洋Sr-87/Sr-86中发挥了作用，特别是发生在darriwilian中期Pygoda serraconodon带（类似于4609 ma +/- 1My）。Sr-87/Sr-86的变化伴随着δ O-18的增加，与气候变冷一致。阐明海底生产对海洋Sr-87/Sr-86的作用以及对奥陶纪冷却的影响，可以更细致地了解驱动数百万年气候变化的因素。(c) 2022 Elsevier B.V.版权所有
The global climate of the Ordovician Period (486.9 to 443.1 Ma) is characterized by cooling that culminated in the Hirnantian glaciation. Chemical weathering of Ca- and Mg-bearing silicate minerals and the subsequent trapping of carbon in marine carbonates act as a sink for atmospheric CO2 on multi-million-year time scales, with basaltic rocks consuming CO2 at a greater rate than rocks of granitic composition. The oceanic Sr isotope ratio (Sr-87/Sr-86) can act as a geochemical proxy for the relative proportion of basaltic versus granitic weathering. Oxygen isotopes (delta O-18) act as a proxy for paleotemperature and ice volume, providing a useful complement to Sr-87/Sr-86 in studies of ancient climate. Previous studies have reported stepwise cooling (increasing delta O-18) during the Middle to Late Ordovician. Combined with Sr and C cycle models, this has led to the hypothesis that continental silicate weathering of mafic material drove Ordovician cooling (e.g., the Taconic Orogeny). However, Sr and C cycle models have not accounted for an apparent rise in sea level and seafloor production in the Middle Ordovician (Darriwilian), which would increase the hydrothermal Sr flux as well as degassing along continental volcanic arcs. Furthermore, some Ordovician studies contain temporal uncertainty between Sr-87/Sr-86 and delta O-18 curves if they are not based on paired analyses, which can obscure the relationship between silicate weathering and cooling. Here, we present new paired Sr-87/Sr-86 and delta O-18 data from conodont apatite and integrate this with both a deterministic (forward) and stochastic (reverse) modeling approach to argue that increased hydrothermal weathering played a role in driving marine Sr-87/Sr-86, specifically an inflection occurring in the Pygoda serraconodont zone of the mid-Darriwilian Stage (similar to 460.9Ma +/- 1My). This Sr-87/Sr-86 inflection is accompanied by an increase in delta O-18, consistent with climate cooling. Clarifying the role of seafloor production for marine Sr-87/Sr-86 and the implications for Ordovician cooling allows for a more nuanced understanding of the factors that drive multi-million-year shifts in climate. (c) 2022 Elsevier B.V. All rights reserved.