Abstract The full potential of the dolomite Ca isotope proxy only unfolds when combined with data of the other main elements (C, O, Mg) in the crystal lattice of Mg-carbonates. Data presented here reveal the level of complexity inherent to dolomite precipitation and alteration environments and add new constraints to the understanding of early diagenetic dolomite formation. Well-constrained Precambrian to Pleistocene dolomites were investigated, representing three characteristic formation and alteration environments: (i) sabkha, (ii) altered marine and (iii) lacustrine/palustrine dolomites. Primary sabkha dolomites with typically low cation ordering degree (COD), high δ13C and low δ44/40Ca values contrast with recrystallized sabkha dolomites with relatively high COD, low δ13C and high δ44/40Ca values. Both δ13C and δ44/40Ca values of sabkha dolomite bear witness to the relative effects of kinetic and equilibrium Ca isotope fractionation conditions. Primary sabkha dolomites display Δ44/40Cadolomite-fluid ranging from −0.4 to −1.3‰, whereas recrystallized dolomite is approaching isotopic equilibrium (Δ44/40Cadolomite-fluid ∼ 0‰). Using the fractionation factor deduced from the sabkha dolomite data set, recrystallized Precambrian dolomite points to a δ44/40Caseawater/pore fluid of about 1.2‰ (SRM 915a), a value that is distinctively lower compared to previously suggested ones and modern seawater. Altered marine dolomites display evidence for meteoric overprint, indicated by δ18O values as low as −4.62‰. Both Mg and Ca isotope signatures correlate with δ18O values of altered marine dolomites, whereas δ13C values lack correlation with the other isotope systems. We propose that freshwater circulated through silicate aquifers prior to reaching the dolostone units and Ca, Mg and O isotopes of altered marine dolomites reflect variable degrees of this meteoric overprint. Lacustrine/palustrine dolomites display a correlation between the isotope values of C, Mg and Ca. These dolomites are formed during pulses of marine ingression in swamp, playa and lake environments and are thus characterized by water-logged conditions (anaerobic) and saline, sulfate-rich fluids. Bacterial-sulfate reduction induces dolomite formation and leads to lower δ13C and δ44/40Ca as well as to higher δ26Mg values. The Ca isotope proxy acts as a benchmark against which other proxy data can be calibrated or processes tested. Taking COD and dolomite stoichiometry into consideration, the here documented multi-proxy isotope approach is promising and provides benchmarks against which proxy signals can be calibrated and tested. Interestingly, even the limited data sets shown here point to patterns that can be interpreted in a meaningful manner that is of relevance for dolomite research.

中文翻译：

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早期成岩白云岩形成和蚀变的控制：多代理δ44/40Ca、δ26Mg、δ18O和δ13C方法

摘要 只有与镁碳酸盐晶格中其他主要元素（C、O、Mg）的数据结合时，白云石 Ca 同位素替代物的全部潜力才会显现。这里提供的数据揭示了白云岩沉淀和蚀变环境固有的复杂程度，并为了解早期成岩白云岩的形成增加了新的限制。研究了受约束的前寒武纪至更新世白云岩，代表了三种特征形成和蚀变环境：(i) sabkha，(ii) 改变的海相和 (iii) 湖相/湖相白云岩。具有典型低阳离子有序度 (COD)、高 δ13C 和低 δ44/40Ca 值的原生 sabkha 白云岩与具有相对高 COD、低 δ13C 和高 δ44/40Ca 值的再结晶 sabkha 白云岩形成对比。sabkha 白云岩的 δ13C 和 δ44/40Ca 值都证明了动力学和平衡 Ca 同位素分馏条件的相对影响。原生sabkha 白云岩显示Δ44/40Cadolomite-fluid 范围从-0.4 到-1.3‰，而重结晶白云岩接近同位素平衡（Δ44/40Cadolomite-fluid ∼ 0‰）。使用从 sabkha 白云岩数据集推导出的分馏因子，再结晶的前寒武纪白云岩表明 δ44/40Caseawater/孔隙流体约为 1.2‰ (SRM 915a)，该值明显低于先前建议的值和现代海水。改变的海洋白云岩显示出陨石叠加的证据，δ18O 值低至 -4.62‰。Mg 和 Ca 同位素特征都与蚀变海相白云岩的 δ18O 值相关，而 δ13C 值与其他同位素系统缺乏相关性。我们认为，淡水在到达白云岩单元之前循环通过硅酸盐含水层，而蚀变海洋白云岩的 Ca、Mg 和 O 同位素反映了这种陨石覆盖的不同程度。湖相/湖相白云岩显示 C、Mg 和 Ca 的同位素值之间存在相关性。这些白云岩是在沼泽、海滩和湖泊环境中海洋入侵的脉冲期间形成的，因此具有浸水条件（厌氧）和含盐、富含硫酸盐的流体的特征。细菌硫酸盐还原诱导白云石形成并导致较低的 δ13C 和 δ44/40Ca 以及较高的 δ26Mg 值。Ca 同位素代理作为基准​​，其他代理数据可以校准或过程测试。考虑到 COD 和白云石化学计量，这里记录的多代理同位素方法很有前途，并提供了可以校准和测试代理信号的基准。有趣的是，即使此处显示的有限数据集也指向可以以与白云岩研究相关的有意义的方式进行解释的模式。