Calcium Isotopic Constraints on the Transition From Aragonite Seas to Calcite Seas in the Cambrian
Calcium Isotopic Constraints on the Transition From Aragonite Seas to Calcite Seas in the Cambrian
复制标题
寒武纪文石海向方解石海转化的钙同位素制约
DOI：
10.1029/2021gb007235
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发表时间：
2022-05
影响因子：
5.2
通讯作者：
Guangyi Wei;Ashleigh v. S. Hood;N. Planavsky;Da Li;H. Ling;L. Tarhan
中科院分区：
文献类型：
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作者：
Guangyi Wei;Ashleigh v. S. Hood;N. Planavsky;Da Li;H. Ling;L. Tarhan
海洋碳酸盐的主要矿物学随着地质时期的变化而变化，与全球气候和海水化学的长期演变相一致。在这里，我们采用了多代理地球化学和岩石学方法，包括测量埃迪卡拉系-寒武系碳酸盐的Ca同位素（δ44Ca）和Sr含量，以提供关于埃迪卡拉系-寒武系从“白云石-文石海”向“方解石海”转变的时间的新见解。我们找到了强有力的证据，证明文石海一直存在到寒武纪 2 纪（甚至可能一直持续到 4 纪）。这些新的 δ44Ca 和 Sr 数据与更新的非生物碳酸盐沉淀物（即鲕质和胶结物）岩相学汇编一起提供了进一步的证据，表明寒武纪存在从文石海到方解石海的长期过渡。我们认为，这种转变部分是由海水镁/钙比的变化所介导的，而海水镁/钙比的变化可能受到全球海洋氧化还原状态和自生粘土降水程度的调节。
The primary mineralogy of marine carbonates has varied over geological time in concert with the secular evolution of global climate and seawater chemistry. Here, we employed a multi‐proxy geochemical and petrographic approach, including measuring the Ca isotope (δ44Ca) and Sr content of Ediacaran–Cambrian carbonates, to provide new insights into the timing of the transition from a “dolomite‐aragonite sea” to a “calcite sea” across the Ediacaran‐Cambrian transition. We find robust evidence for the persistence of an aragonite sea well into Cambrian Age 2 (and potentially up through Age 4). Together with an updated petrographic compilation of abiotic carbonate precipitates (i.e., ooids and cements), these new δ44Ca and Sr data provide further evidence that there was a protracted transition from aragonite seas to calcite seas in the Cambrian. We propose that this transition was mediated, in part, by changes in seawater Mg/Ca ratios potentially regulated by the global marine redox state and extents of authigenic clay precipitation.