Early diagenesis of corals generated by variable activity of endolithic algae and its impact on geochemical proxies.

由内石藻的可变活动产生的珊瑚的早期成岩作用及其对地球化学指标的影响。

• 批准号: 218476762
• 负责人: Professor Dr. Anton Eisenhauer
• 金额: --
• 依托单位: GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel
• 依托单位国家: 德国
• 项目类别: Research Units
• 财政年份: 2013
• 资助国家: 德国
• 起止时间: 2012-12-31 至 2020-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/218476762?language=en
• 关键词: Early; diagenesis; corals; generated; variable

Aragonitic corals are widely considered as suitable archives of their past marine environment and as monitors of sea-level evolution. Variations in the chemical and isotope signatures of the skeleton can be calibrated to environmental parameters such as seawater temperature, salinity, and pH at time of coral biomineral secretion. The geochemical proxy approach on scleractinian corals is challenged because actual studies dealing with early coral diagenesis revealed that mineralogical and chemical alteration may commence immediately post mortem or even in the skeleton underneath living corals, prior to burial or sub-aerial exposure.. Evidence for this comes among others from trace element ratios significantly differing in their proxy information for initially cogenetic skeleton parts. Previous workers have discussed mainly physico-chemical processes including diagenesis of primary biogenic aragonite, ingrowth of abiogenic aragonite, dissolution of the primary coral skeleton, recrystallization and transformation to secondary calcite. We argue that these processes should be readdressed from the viewpoint of early biogenic factors, specifically the role of endolithic algae on coral carbonate diagenesis. Endolithic algae constitute a common feature of tropical corals, living within the skeleton pore space. Algae activity within the coral includes skeleton dissolution and pH increase by photosynthesis. The latter is inducing precipitation of secondary phases with chemical signatures outside coral specific fractionation systematics. Consequently, both processes may strongly influence the carbonate stability and proxy record reliability, potentially representing a significant impact on early coral diagenesis and proxy calibration approaches.This study benefits from an innovative combination of low- and high-resolution techniques for structural and mineralogical investigation, as well as for element and isotope geochemical analyses. The obtained data will provide a comprehensive understanding of pore volume characteristics and mineralogical composition as basis for the interpretation of spatial variations in elemental (Li/Ca, B/Ca, Mg/Ca, Sr/Ca, I/Ca Ba/Ca U/Ca,) and isotope geochemical proxies (delta11B, delta13C, delta18O, delta26Mg, delta44/40Ca, delta88/86Sr, 87Sr/86Sr, U-Th geochronology). From these results we aim to achieve a detailed understanding of the impact of endolithic algae activity on coral early diagenesis.

文石珊瑚被广泛认为是其过去海洋环境的适当档案，并作为海平面演变的监测器。骨骼的化学和同位素特征的变化可以根据环境参数进行校准，例如珊瑚生物矿物分泌时的海水温度，盐度和pH值。石珊瑚的地球化学代用方法受到挑战，因为有关早期珊瑚成岩作用的实际研究表明，矿物和化学变化可能在死后立即开始，甚至在埋葬或暴露于空气中之前，在活珊瑚下面的骨骼中也可能开始。这方面的证据来自微量元素的比例显着不同的代理信息最初同源的骨骼部分。前人主要讨论了原生生物文石的成岩作用、无机文石的长入作用、原生珊瑚骨架的溶解作用、重结晶作用和次生方解石的转化等物理化学过程。我们认为，这些过程应该重新处理的观点，早期的生物因素，特别是珊瑚碳酸盐成岩作用的石内藻类。内石藻类是热带珊瑚的共同特征，生活在骨骼孔隙中。珊瑚中的藻类活动包括骨骼溶解和光合作用引起的pH值升高。后者是诱导沉淀的第二阶段的化学签名以外的珊瑚具体分馏系统。因此，这两个过程可能会强烈影响碳酸盐岩的稳定性和代理记录的可靠性，可能代表早期珊瑚成岩作用和代理calibration approaches.This study benefits from a innovative combination of low- and high-resolution techniques for structural and mineralogical investigation，以及元素和同位素地球化学分析。所获得的数据将提供对孔隙体积特征和矿物组成的全面了解，作为解释元素（Li/Ca、B/Ca、Mg/Ca、Sr/Ca、I/Ca、Ba/Ca、U/Ca）和同位素地球化学代用指标（δ 11 B、δ 13 C、δ 18 O、δ 26 Mg、δ 44/40 Ca、δ 88/86 Sr、87 Sr/86 Sr、U-Th年代学）空间变化的基础。从这些结果中，我们的目标是实现详细了解的影响，石内藻类活动对珊瑚早期成岩作用。