Early-marine diagenetic dolomitisation of a giant Upper Triassic carbonate platform

经过均匀的早成岩海相孔隙水白云化作用，区域范围广泛（100公里）和厚度（1000米）的碳酸盐岩台地是许多Myr时期被动边缘和表海的典型代表。大量沉积和生物源CaCO3向（钙质）白云岩的海相成岩转化是碳酸盐岩研究中最有趣的过程之一。替代的早成岩白云岩以细晶、保存织物的“白云岩”的马赛克形式存在，与后期埋藏的白云岩明显不同。这里提出的研究重点是阿尔卑斯地区的Norian“Dolomia Principale”的杰出案例，特别是伦巴第盆地，它使显生宙的大多数早成岩白云化台地相形见绌。主要白云岩具有以下特点：早成岩白云化作用均匀地影响所有台地内部、台地边缘和斜坡碳酸盐，而台地内盆地沉积为钙质沉积；白云化作用将该台地与下伏（卡尼期）和上伏（雷蒂亚期）的台地区分开来，其特征是部分白云化的潮缘台地内灰岩相。复杂的水深测量（台地内部与台地内部盆地）允许研究白云化机制的模式（回流、sabkha、修正混合带、微生物诱导的白云化等）。所涉及的过程可能相互作用非常复杂，但我们认为它们是确定性的。我们将应用详细的野外和岩心沉积学和岩石学，使用来自内平台、边缘、微生物堆积、斜坡角砾岩（都是白云化的）和盆地灰岩等关键位置的样本。样品将通过涉及CaMgCO3所有主要元素的多代理同位素-地球化学和元素方法进行研究。正如我们在之前的工作中所记载的那样，详细的沉积学、岩石学、水泥地层学和地球化学相结合，对评估这些样品的成岩途径和白云化机制具有重要的潜力。在项目第二年末和第三年期间，地层正向和反应性输运模型（与项目伙伴合作）将把数据及其解释置于本研究对象之外的更广泛的背景下。这个项目雄心勃勃（但可行）。它的目的是系统和机械地评估早期海洋成岩白云化过程，在区域和地形复杂的背景下，广泛的平台系统记录了海洋替代白云化的时间尺度为15兆年。我们建议，该项目得出的数据和科学可以作为该研究领域未来研究的模板。

Regionally extensive (100s of km) and thick (1000s of m) carbonate platforms that have undergone homogeneous, early-diagenetic marine porewater dolomitisation typify passive margins and epeiric seas over periods of many Myr. The marine-diagenetic transformation of very large volumes of sedimentary and biogenic CaCO3 to (calcian) dolomite is one of the most intriguing processes in carbonate research. Replacive, early-diagenetic dolostones are present as mosaics of fine-crystalline, fabric-preserving `dolomicrite’ differing significantly from later burial dolomite. The research proposed here focuses on the outstanding case example of the Norian `Dolomia Principale´ in the Alpine domain, specifically the Lombardy Basin, that dwarfs most other early-diagenetic dolomitised platforms of the Phanerozoic. Several features set the Dolomia Principale apart: The early-diagenetic dolomitisation homogeneously affects all inner platform, platform-margin and slope carbonates, while intraplatform basin deposits are calcitic. Dolomitisation discriminates this platform from the underlying (Carnian) and overlying (Rhaetian) ones, characterised by partially dolomitised peritidal inner-platform limestone facies. The complex bathymetry (inner platform versus intra-platform basins) allows studying patterns in the dolomitisation mechanism (reflux, sabkha, revised mixing zone, microbially-induced dolomitisation etc.). The processes involved likely interacted highly complexly, but we argue that they are deterministic. We will apply detailed field and core sedimentology and petrography using samples from key locations in the inner platform, the margin, microbial buildups, slope breccia (all dolomitised) and basinal limestones. Samples will be studied through a multiproxy isotope-geochemical and elemental approach involving all major elements of CaMgCO3. As documented in our previous work, the combination of detailed sedimentology, petrography, cement stratigraphy and geochemistry has a significant potential to assess these samples’ diagenetic pathways and dolomitisation mechanisms. Towards the end of year two and during the third project year, stratigraphic forward and reactive transport modelling (in cooperation with project partners) will place the data and their interpretation in a wider context beyond this study object. The project is ambitious (yet feasible). It aims to systematically and mechanistically assess the process of early marine-diagenetic dolomitisation in the context of a regionally and topographically complex, widespread platform system that recorded marine replacement dolomitisation over time scales of 15 Myr. We suggest that data and science resulting from this project can serve as a template for future studies in this research field.