Unraveling the sulfur cycle with carbonates: mechanism of incorporation and diagenesis of structurally-substituted-sulfate

海洋碳酸盐是关于海洋的物理和化学特征以及大气成分和全球气候变化方面重建地球系统演化的中心档案。生物碳酸盐、碳酸盐胶结物和泥晶都被用来重建各自的海水性质。除了碳、氧或锶等更经典的同位素替代物外，越来越多的研究利用微量硫酸盐来重建海水硫酸盐随时间推移的硫同位素组成。更重要的是，个别研究将提取的硫酸盐数量解释为反映了最初的海洋硫酸盐丰度。虽然经验证据表明，硫同位素组成确实反映了碳酸盐沉积时大洋硫酸盐的同位素组成，但对硫酸盐并入的机制和边界条件尚无确切的认识。此外，碳酸盐岩还受沉积后成岩蚀变的影响。然而，对碳酸盐中这种微量成分的丰度和同位素组成的各自影响在很大程度上是未知的。这里提出的实验和经验工作旨在揭示硫酸盐作用及其沉积后改变的各自细节，以便对其作为重建地球系统演化的替代指标的适用性施加严格的限制。

Marine carbonates represent the central archive for reconstructing Earth System evolution in respect to the physical and chemical characteristics of the oceans as well as changes in atmospheric composition and global climate. Biogenic carbonates, carbonate cements and micrites alike have been utilized for reconstructing respective seawater properties. Aside more classical isotopic proxies such as carbon, oxygen, or strontium, an increasing number of studies utilizes trace quantities of sulfate in order to reconstruct the sulfur isotopic composition of seawater sulfate through time. Even more, individual studies interpreted the amount of extracted sulfate as a reflection of the initial oceanic sulfate abundance. Although empirical evidence suggests that the sulfur isotopic composition indeed reflects the isotopic composition of oceanic sulfate at the time of carbonate deposition, no firm understanding about the mechanism of as well as the boundary conditions for sulfate incorporation exists. Furthermore, carbonates are subject to post-depositional diagenetic alteration. Yet, respective effects on the abundance and isotopic composition of this trace constituent in carbonates are largely unknown. Experimental and empirical work proposed here aims at unravelling respective details of sulfate incorporation and its post-depositional alteration in order to place firm constraints on the applicability as a proxy for reconstructing Earth System evolution.