Selective dolomitization of HMC allochems in Neogene carbonates is a common phenomenon. It has been proposed that the higher magnesium concentrations [Mg] in these allochems promotes dolomitization. To directly investigate the effects of [Mg] (reported as mol% MgCO3) in biogenic HMC on dolomitization, high-temperature (200 °C) dolomitization experiments were conducted. Dolomite reaction rate, stoichiometry, and microstructures were tracked during dolomitization for a variety of biogenic HMC reactants, including Goniolithon, Lithothamnion, Lithophyllum, Corallina officinalis, Heterocentrotus mamillatus, and Mellita quinquiesperforata. Solids were characterized using standard powdered X-ray diffraction (XRD) and scanning electron microscopy (SEM). In general, biogenic HMC reactants are progressively replaced by protodolomite products between 2 and 46 hours. In the experiment using Corallina officinalis, no products were detected by XRD after 46 hours. Initial protodolomite products are subsequently replaced by ordered dolomite as the reactions proceed. Dolomitization rate and protodolomite stoichiometry do not correlate with [Mg] of the biogenic HMC reactants. Dolomitized HMC skeletons reliably retain the original microstructure of the HMC reactants, consistent with the microcrystalline mimetic textures observed in nature. These findings collectively suggest that under the conditions investigated, dolomitization is less affected by the concentration of magnesium in the HMC reactants relative to other known factors, such as temperature, reactant mineralogy, organic content, skeletal texture, and fluid chemistry. These results imply that the observed correlation between coralline red algae abundance and global dolomitization events in the Neogene is not driven by the elevated magnesium concentration of the HMC reactants.

中文翻译：

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高镁方解石异化物中镁浓度对白云石化的影响：来自高温白云石合成实验的见解

新近纪碳酸盐岩中 HMC 异质化合物的选择性白云石化是普遍现象。有人提出，这些异种化合物中较高的镁浓度 [Mg] 会促进白云石化。为了直接研究生物成因 HMC 中 [Mg]（报告为 mol% MgCO3）对白云石化的影响，进行了高温（200 °C）白云石化实验。白云石反应速率、化学计量和微观结构在白云石化过程中跟踪了各种生物 HMC 反应物，包括 Goniolithon、Lithothamnion、Lithophyllum、Corallina officinalis、Heterocentrotus mamillatus 和 Mellita quinquiesperforata。使用标准粉末 X 射线衍射 (XRD) 和扫描电子显微镜 (SEM) 表征固体。一般来说，生物源 HMC 反应物在 2 到 46 小时内逐渐被原白云石产物取代。在使用 Corallina officinalis 的实验中，46 小时后 XRD 未检测到任何产物。随着反应的进行，最初的原白云石产物随后被有序白云石取代。白云石化速率和原白云石化学计量与生物 HMC 反应物的 [Mg] 无关。白云石化的 HMC 骨架可靠地保留了 HMC 反应物的原始微观结构，与自然界中观察到的微晶模拟纹理一致。这些发现共同表明，在所研究的条件下，白云石化受 HMC 反应物中镁浓度的影响相对于其他已知因素（如温度、反应物矿物学、有机物含量、骨骼结构、和流体化学。这些结果意味着在新近纪中观察到的珊瑚红藻丰度与全球白云石化事件之间的相关性并非由 HMC 反应物的镁浓度升高所驱动。