Formation and diagenetic evolution of actualistic, aragonite-cemented seafloor carbonates

现实的文石胶结海底碳酸盐的形成和成岩演化

• 批准号: 435379576
• 负责人: Professor Dr. Adrian Immenhauser
• 金额: --
• 依托单位: School of Ocean Sciences
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/435379576?language=en
• 关键词: Formation; diagenetic; evolution; actualistic; aragonite

Discontinuity surfaces and their related hiatus intervals represent complex and very common features in shallow marine depositional environments. This proposal focusses on actualistic, aragonite-cemented hardgrounds in the lagoon and intertidal sabkha of Abu Dhabi. In the terminology of sequence stratigraphy, these qualify as transgressive surfaces or parasequence boundaries. Preliminary work by the proponent and collaborators has documented that these features are highly complex and spatially-variable both with respect to their formation and hardground cement petrography. Commonly-applied models of hardground formation fail to describe the wide range of features observed. Our data document a hitherto unknown but very characteristic trend in hardground cement morphology, ranging from needle aragonite in the outer lagoon to platy and pseudo-hexagonal cements in the inner lagoon. Next to conventional marine hardgrounds (i.e. early diagenetic lithification and subsequent encrustation and bioperforation of the seafloor), evidence for what here are referred to as “non-conventional hardgrounds” is presented. These features form as concretionary layers within the sediment column beneath the porewater redoxcline some tens of centimetres beneath the seafloor. There, precipitation of complex aragonite cements is related to the activity of sulfate-reducing bacteria, the removal of inhibitors, and an increase in alkalinity. This finding is relevant as fossil concretionary layers might be mistaken as marine omission surfaces leading to erroneous palaeoenvironmental interpretations. The presence of a suite of Recent to Pleistocene hardground features allows for a time-resolved assessment of the diagenetic history of early marine, aragonite cemented intervals. Pleistocene hardgrounds are typified by corroded precursor cements and neoformed, rhombohedral calcites, a diagenetic succession that merits detailed investigation. The field sedimentological, petrographic, and geochemical study considers seawater and porewater properties in relation to early diagenetic carbonate phases. In order to shed light on parameters that control the uncommon cement morphologies, we collaborate with colleagues from the Technical University of Graz performing abiogenic precipitation experiments. We further rely on collaboration with colleagues at Newcastle University to provide expertise in microbiogeology in the context of an independent twin project. The aim is to disentangle the complex array of physical, chemical, and microbiological parameters on fluid properties and cement precipitation kinetics. Research proposed here has wider relevance as most studies of fossil hardground have focussed on well-preserved, calcite-cemented discontinuities. In contrast, research dealing with actualistic and fossil aragonite-cemented hardgrounds, and specifically the physico-chemical parameters of their formation and diagenetic evolution, is as yet insufficiently developed.

不连续面及其相关的间断间隔是浅海沉积环境中复杂且非常常见的特征。该提案的重点是阿布扎比泻湖和潮间带sabkha的现实主义，文石胶结硬地。在层序地层学的术语中，它们被称为海侵面或准层序界面。提议者和合作者的初步工作证明，这些特征在其形成和硬地面水泥岩相学方面都非常复杂和具有空间可变性。硬地地层的常用模型无法描述所观察到的各种特征。我们的数据文件迄今未知的，但非常典型的趋势，硬地水泥形态，从针文石在外部泻湖板状和假六角水泥的内部泻湖。除了常规的海洋硬地（即早期成岩岩化作用和随后的结壳作用以及海底生物穿孔作用）之外，还提出了这里所称的“非常规硬地”的证据。这些特征形成为海底下几十厘米处孔隙水氧化还原跃层下沉积柱内的结核层。在那里，沉淀的复杂的文石水泥有关的硫酸盐还原菌的活性，抑制剂的去除，并增加碱度。这一发现是相关的，因为化石结核层可能被误认为是海洋遗漏的表面，导致错误的古环境解释。一套最近更新世硬地面功能的存在允许一个时间分辨的评估成岩历史的早期海洋，文石胶结间隔。更新世硬地的典型特征是受腐蚀的前体胶结物和新形成的菱面体方解石，这是一种值得详细研究的成岩序列。野外沉积学、岩相学和地球化学研究考虑了海水和孔隙水与早期成岩碳酸盐相的关系。为了阐明控制不常见的水泥形态的参数，我们与来自格拉兹技术大学的同事合作进行非生物沉淀实验。我们进一步依靠与纽卡斯尔大学的同事合作，在一个独立的双胞胎项目的背景下提供微生物学方面的专业知识。目的是解开复杂的物理，化学和微生物参数对流体性质和水泥沉淀动力学。这里提出的研究具有更广泛的相关性，因为大多数化石硬地的研究都集中在保存完好的方解石胶结的不连续面上。与此相反，研究处理现实和化石文石胶结硬地，特别是其形成和成岩演化的物理化学参数，尚未充分发展。