Abstract As an important family of elements, halogens (Cl, Br, and I) have been widely used to study geological processes, particularly in high-temperature environments, showing great prospects either in fundamental or in applied studies. However, little work has been conducted for sedimentary and low-temperature diagenetic environments re-construction although these elements have the potential in theory. Here we perform a pilot study on this issue using a case study of Middle Triassic marine dolomitization in South China. Our results show that the average Cl concentrations in limestone, dolomitic limestone, calcitic dolomite and dolomite are 88.3 ppm, 114.7 ppm, 121.3 ppm and 142.9 ppm respectively, and the corresponding Br concentrations are 1.15 ppm, 1.42 ppm, 1.59 ppm and 2.13 ppm, respectively. Both the concentrations of Cl and Br increased with the increasing dolomitization degree. The increasing tendency of Cl and Br is similar to the seawater evaporation trajectory before halite precipitation, indicating that dolomitization occurs in fluids with elevated salinity. Meanwhile, the difference of Cl/Br ratios between our carbonate samples and seawater may be ascribed to the input of terrestrial water, which has variable Cl/Br ratios. As for the concentration of I, the mean values sharply decreased from 0.36 ppm in limestone to 0.13 ppm in dolomitic limestone samples, and it further lowered to 0.09 ppm and 0.08 ppm in calcitic dolomite and dolomite samples, respectively. The calculated I/(Ca + Mg) ratios in limestones vary between 0.05 and 0.58 μmol/mol with an average value of 0.29 μmol/mol, indicating that limestone formed in open ocean oxygen-minimum zone (OMZs) or anoxic basin environment. The average I/(Ca + Mg) ratio decreases from 0.29 μmol/mol in limestone to 0.06 μmol/mol in dolomite, serving as an important case that dolomitization decreases I/(Ca + Mg) ratios of carbonates rocks. Halogens in carbonates therefore have promising potential for investigating the sedimentary and diagenetic environments of carbonate rocks.

中文翻译：

---

中三叠统碳酸盐岩中的卤素（Cl、Br 和 I）地球化学：对 I/(Ca + Mg) 比值的盐度和成岩改变的影响

摘要 作为重要的元素族，卤素（Cl、Br、I）已被广泛用于研究地质过程，特别是在高温环境中，无论是在基础研究还是应用研究中都具有广阔的前景。然而，尽管这些元素在理论上具有潜力，但在沉积和低温成岩环境重建方面的工作却很少。在这里，我们使用华南中三叠统海相白云石化的案例研究对这个问题进行了试点研究。我们的研究结果表明，石灰石、白云质石灰岩、方解石白云石和白云石中的平均 Cl 浓度分别为 88.3 ppm、114.7 ppm、121.3 ppm 和 142.9 ppm，相应的 Br 浓度分别为 1.15 ppm、1.42 ppm、1.519 ppm 和 1.519 ppm。分别。Cl和Br的浓度随着白云石化程度的增加而增加。Cl和Br的增加趋势与岩盐沉淀前的海水蒸发轨迹相似，表明白云石化发生在盐度升高的流体中。同时，我们的碳酸盐样品和海水之间的 Cl/Br 比值的差异可能归因于陆地水的输入，其具有可变的 Cl/Br 比值。对于I的浓度，平均值从石灰石的0.36 ppm急剧下降到白云质石灰岩样品的0.13 ppm，并进一步降低到方解石白云石和白云石样品的0.09 ppm和0.08 ppm。石灰石中计算的 I/(Ca + Mg) 比率在 0.05 和 0.58 μmol/mol 之间变化，平均值为 0.29 μmol/mol，表明石灰岩形成于开阔洋最低氧区 (OMZ) 或缺氧盆地环境。平均 I/(Ca + Mg) 比值从石灰岩的 0.29 μmol/mol 降低到白云岩的 0.06 μmol/mol，是白云石化降低碳酸盐岩 I/(Ca + Mg) 比值的一个重要例子。因此，碳酸盐中的卤素在研究碳酸盐岩的沉积和成岩环境方面具有广阔的前景。