Limestone–marl alternations are commonly used for high-resolution cyclostratigraphic studies and palaeoenvironmental reconstructions, but diagenetic studies indicate that not all limestone–marl alternations reflect genuine differences in the initial sediment composition driven by environmental changes. Differences in the ratios of diagenetically inert trace elements between limestones and marls indicate changes affecting the terrigenous fraction of the precursor sediment. Contrarily, limestone–marl alternations without these differences can be the product of: (i) variations in CaCO₃ input (aragonite, calcite); (ii) distortion of the latter by diagenetic CaCO₃ redistribution; or (iii) diagenetic CaCO₃ redistribution in a homogeneous precursor sediment. The aim of this study is to provide a method to differentiate these cases and to identify variations in the proportion of calcite and aragonite in the precursor sediment composition. The model of differential diagenesis assumes that the concentration of diagenetically inert elements is inversely proportional to the amount of redistributed CaCO₃. Consequently, the difference between ratios of diagenetically inert elements from two adjacent beds is a measure for CaCO₃ redistribution. This is quantifiable by the vector length between ratios from two adjacent beds. The approach is illustrated here by evaluation of a case study from the Silurian of Gotland, Sweden. Trace elements were compared according to their solubility during diagenesis. All elements bound to clay minerals or calcite show similar patterns of vector length, while vector length of elements which fit into the aragonite lattice, and are diagenetically mobile, differ. The vector length approach provides a tool to test the diagenetic origin of limestone–marl alternations, to identify initial variations in CaCO₃ input and to test a limestone–marl alternation’s suitability for cyclostratigraphic analyses.

中文翻译：

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检测石灰石-泥灰岩交替中的初始文石和方解石变化

石灰岩-泥灰岩交替常用于高分辨率旋回地层研究和古环境重建，但成岩研究表明，并非所有石灰岩-泥灰岩交替都反映了由环境变化驱动的初始沉积物成分的真正差异。石灰岩和泥灰岩之间成岩惰性微量元素比率的差异表明影响前体沉积物陆源部分的变化。相反，没有这些差异的石灰石-泥灰交替可能是以下因素的产物：(i) CaCO ₃输入（文石、方解石）的变化；(ii) 后者因成岩 CaCO ₃再分布而变形；或 (iii) 成岩 CaCO ₃在均匀的前体沉积物中重新分布。本研究的目的是提供一种方法来区分这些情况并确定前体沉积物成分中方解石和文石比例的变化。差异成岩模型假设成岩惰性元素的浓度与重新分布的 CaCO ₃的量成反比。因此，来自两个相邻床层的成岩惰性元素比率之间的差异是 CaCO ₃的量度再分配。这可以通过来自两个相邻床的比率之间的向量长度来量化。此处通过对瑞典哥特兰志留纪的案例研究进行评估来说明该方法。微量元素根据它们在成岩过程中的溶解度进行比较。所有与粘土矿物或方解石结合的元素都显示出相似的矢量长度模式，而适合文石晶格的元素的矢量长度则不同。矢量长度方法提供了一种工具来测试石灰岩-泥灰岩交替的成岩成因，识别 CaCO ₃输入的初始变化，并测试石灰岩 - 泥灰岩交替对旋回地层分析的适用性。