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区间代表了浅海沉积环境中复杂且非常常见的特征，该提案重点关注阿布扎比泻湖和潮间带的实际硬地层，这些硬地层在层序地层学术语中属于海侵地层。支持者和合作者的初步工作已经证明这些特征非常复杂且空间可变。硬地层形成和硬地水泥岩相学的常用模型无法描述观察到的广泛特征，我们的数据记录了硬地水泥形态的迄今为止未知但非常典型的趋势，从外泻湖的针状霰石到片状。内泻湖中的伪六边形胶结物（即早期成岩岩化和随后的海底结壳和生物穿孔）的证据。这些特征在海底数十厘米处的孔隙水氧化还原线下方的沉积物柱内形成，复杂的文石胶结物的沉淀与碳酸盐的活动有关。硫酸盐还原菌、抑制剂的去除以及碱度的增加这一发现是相关的，因为化石结核层可能被误认为是海洋遗漏表面，从而导致。错误的古环境解释。一系列近更新世硬地层特征的存在可以对早期海洋文石胶结层段的成岩历史进行时间分辨评估，其特征是腐蚀的前体胶结物和新形成的菱形方解石（一种成岩作用）。值得详细研究的演替过程包括海水和地球化学研究。与早期成岩碳酸盐相相关的孔隙水特性为了揭示控制不常见胶结物形态的参数，我们与格拉茨技术大学的同事合作进行了非生物沉淀实验。在一个独立的双胞胎项目中提供微生物地质学方面的专业知识，其目的是理清流体特性和水泥沉淀动力学的一系列复杂的物理、化学和微生物参数，因为大多数化石研究具有更广泛的相关性。硬地层的研究重点是保存完好的方解石胶结断面，相比之下，有关现实和化石文石胶结硬地层的研究，特别是其形成和成岩演化的物理化学参数，尚未得到充分发展。