Progress towards an improved Precambrian seawater 87Sr/86Sr curve
Progress towards an improved Precambrian seawater 87Sr/86Sr curve
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DOI：
10.1016/j.earscirev.2021.103869
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发表时间：
2022-01-01
影响因子：
12.1
通讯作者：
Shields, Graham A.
中科院分区：
文献类型：
--
作者：
Chen, Xi;Zhou, Ying;Shields, Graham A.
海水锶同位素比值（Sr-87/Sr-86）的长期变化趋势反映了大陆与地幔储层对海洋成分相对贡献的变化，并为全球构造事件、风化速率和地球化学循环提供了信息。然而，前寒武纪海水Sr-87/Sr-86曲线的细节远不如它的古生代对应物。在这项研究中，我们汇编了自2002年以来发表的前寒武纪海洋沉积岩的2249个锶同位素比值，以及以前汇编的旧数据。在这里，我们评估的不确定性，所有已公布的数据约束同时代海水Sr-87/Sr-86使用四个标准（沉积环境，成岩蚀变，年龄限制和溶解方法）。所得海水Sr-87/Sr-86曲线主要使用“高确定性”数据，并显示出c处从~0.7005开始的总体增加趋势。3.5 Ga到> 0.7089接近埃迪卡拉纪末期。改进后的曲线显示海水Sr-87/Sr-86较早偏离同生地幔约c. 3.5 Ga，这可能反映了与新生构造有关的演化大陆地壳的首次重要出现。此外，更新后的曲线记录了2.5-2.2 Ga和1.9-1.7 Ga的两次主要上升，以及0.8-0.5 Ga的一次明确事件。尽管相对稀缺的高确定性的数据，这两个增加是一致的增强大陆风化后的氧化风化和组装的超大陆努纳，分别开始。虽然这两个事件的确认等待更高的确定性数据，前寒武纪海水Sr-87/Sr-86经历了更强的振荡和更好的对应关系，与超大陆周期比以前显示。
The secular trend of seawater strontium isotope ratio (Sr-87/Sr-86) reflects changes in the relative contributions of continental versus mantle reservoirs to ocean composition, and informs global tectonic events, weathering rates and biogeochemical cycling through Earth history. However, the Precambrian seawater Sr-87/Sr-86 curve is known in far less detail than its Phanerozoic counterpart. For this study, we compiled 2249 strontium isotope ratios of Precambrian marine sedimentary rocks published since 2002, alongside previously compiled older data. Here we evaluate the uncertainty of all published data for constraining coeval seawater Sr-87/Sr-86 using four criteria (depositional environment, diagenetic alteration, age constraint and dissolution method). The resultant seawater Sr-87/Sr-86 curve uses mainly 'high certainty' data and shows an overall increasing trend from ~0.7005 at c. 3.5 Ga to > 0.7089 towards the end of the Ediacaran Period. The improved curve shows an earlier deviation of seawater Sr-87/Sr-86 from the contemporaneous mantle by c. 3.5 Ga, which might reflect the first significant emergence of evolved continental crust related to nascent tectonics. Additionally, the updated curve records two major rises at 2.5-2.2 Ga and 1.9-1.7 Ga in addition to a well-established event at 0.8-0.5 Ga. Despite the relative scarcity of high-certainty data, these two increases are consistent with enhanced continental weathering following the onset of oxidative weathering and assembly of the supercontinent Nuna, respectively. Although confirmation of these two events awaits more high-certainty data, Precambrian seawater Sr-87/Sr-86 experienced stronger oscillations and better correspondence with supercontinent cycles than previously shown.