Various geochemical proxies are used to constrain the diagenetic origin and evolution of ancient dolomites. Dolomite stoichiometry (mole % MgCO3) and cation ordering, two mineralogical attributes that define dolomite, have also been shown to demonstrate utility in this regard. Observations from laboratory experiments and field studies suggest that these attributes broadly reflect the fluid chemistry and temperature of the dolomitizing environment. The degree to which these parameters reflect global conditions during dolomitization (e.g., seawater chemistry, eustasy, atmospheric pCO2) and long-term geological processes is poorly understood, however. Here, a large dataset consisting of mineralogical data from over 1,690 Phanerozoic dolomites from various geographic locations, stratigraphic ages, platform types, and depositional environments are queried to investigate the broader geological controls on dolomite stoichiometry and cation ordering in dolomites formed by early, near-surface dolomitization. A suite of statistical analyses performed on the global dataset indicate: 1) despite wide ranges at the eon, period, and epoch level, dolomite stoichiometry and cation ordering broadly increase with geologic age; 2) significant variations in dolomite stoichiometry and cation ordering throughout the Phanerozoic do not correlate with global parameters, such as seawater chemistry, eustasy, orogenic events, and ocean crust production; 3) dolomites associated with restricted depositional settings, such as restricted lagoons, and the intertidal and supratidal zones, are more stoichiometric than dolomites associated with open marine settings, such as the deep-subtidal and shallow-subtidal zones; and 4) dolomites from shallow ramps and epeiric carbonate platforms are generally more stoichiometric than dolomites from open shelves and isolated carbonate platforms. These observations permit a number of inferences to be drawn. First, the principal signal observed in the data is that local environmental conditions associated with platform type and depositional setting are the strongest control on dolomite mineralogy. The observation that more stoichiometric dolomites correlate with shallow and restricted depositional environments is consistent with laboratory experiments that show environmental factors, such as higher Mg:Ca, temperature, and salinity of the dolomitizing fluids yield more stoichiometric dolomite. Second, a weaker secondary signal is also observed such that dolomite stoichiometry and cation ordering both increase with geologic age, suggesting that progressive recrystallization driven by mineralogical stabilization during burial is also occurring. Collectively, these data suggest that spatial and temporal variations in stoichiometry and cation ordering reflect the interplay between local dolomitizing conditions near the surface and long-term mineralogical stabilization during burial.

中文翻译：

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通过显生宙对白云石化学计量和阳离子排序的全球研究

各种地球化学指标被用来限制古代白云岩的成岩起源和演化。白云石化学计量（摩尔 % MgCO3）和阳离子排序，这两个定义白云石的矿物学属性，也已证明在这方面具有实用性。实验室实验和现场研究的观察表明，这些属性广泛地反映了白云石化环境的流体化学和温度。然而，这些参数在多大程度上反映了白云石化过程中的全球条件（例如，海水化学、eustasy、大气 pCO2）和长期地质过程，我们知之甚少。在这里，一个大型数据集由来自不同地理位置、地层年龄、台地类型的 1,690 多个显生宙白云岩的矿物学数据组成，查询和沉积环境以研究对由早期近地表白云石化形成的白云岩中白云岩化学计量和阳离子排序的更广泛的地质控制。对全球数据集进行的一系列统计分析表明：1) 尽管在 eon、period 和 epoch 水平上存在很大范围，但白云岩的化学计量和阳离子排序随着地质年龄的增加而广泛增加；2) 整个显生宙白云岩化学计量和阳离子排序的显着变化与全球参数无关，例如海水化学、eustasy、造山事件和海洋地壳生产；3) 与受限沉积环境相关的白云岩，如受限泻湖、潮间带和潮上带，比与开放海洋环境相关的白云岩更具化学计量比，如深潮下带和浅潮下带；4) 浅斜坡和表层碳酸盐台地的白云岩通常比开放式陆架和孤立的碳酸盐台地的白云岩具有更高的化学计量比。这些观察结果允许得出一些推论。首先，在数据中观察到的主要信号是与平台类型和沉积环境相关的当地环境条件是对白云岩矿物学的最强控制。更多化学计量白云岩与浅层和受限沉积环境相关的观察结果与实验室实验一致，实验室实验表明环境因素，例如较高的 Mg:Ca、温度和白云石化流体的盐度会产生更多的化学计量白云岩。第二，还观察到较弱的次生信号，即白云石化学计量和阳离子排序都随着地质年龄而增加，这表明埋藏期间矿物学稳定驱动的渐进再结晶也在发生。总的来说，这些数据表明化学计量和阳离子排序的空间和时间变化反映了地表附近局部白云石化条件与埋藏期间长期矿物学稳定之间的相互作用。