Modern phosphogenesis occurs on continental margins influenced by upwelling and high primary productivity. The formation of phosphatic sediments is coupled to global climate fluctuations, biological cycling of phosphorus and local redox conditions. Although the processes involved in phosphogenesis are well described, high-resolution data on the redox and stable isotope systematics in Recent in-situ phosphorites are scarce. In this contribution, we investigate the trace element and sulfur, nitrogen and organic carbon stable isotope composition of Recent in-situ phosphatic sediments off the coast of Namibia. Also, we examine the reliability of different widely used geochemical proxies in phosphatic sediments. Our results suggest a shift from sulfidic to suboxic conditions, coinciding with the maximum in solid calcium phosphate mineral concentration. This shift is accompanied by unidirectional changes in Mo and Re enrichments and TOC abundance. Relatively low pyrite δ³⁴S values (ca −20‰) of phosphatic sediments indicate open system fractionation during phosphogenesis. The initiation of phosphogenesis is also accompanied by negative shifts in sedimentary δ¹³C_org and δ¹⁵N values. Phosphate associated sulfate (PAS) δ³⁴S values are lower than modern seawater sulfate values, suggesting the involvement of chemolithotrophic sulfur oxidation. Our results show a shift in redox conditions from sulfidic to (sub)oxic, coupled with active sulfur cycling are prerequisites for phosphogenesis. Phosphatic sediments show substantial enrichments in U and V highlighting the complexity of using these elements, as well as V/(V + Ni) and V/Cr, as redox proxies particularly in phosphorites and phosphatic sediments.

现代的磷化作用发生在受上升流和高初级生产力影响的大陆边缘。磷沉积物的形成与全球气候波动，磷的生物循环和局部氧化还原条件有关。尽管很好地描述了与磷发生有关的过程，但有关近距离原位亚磷酸盐中氧化还原和稳定同位素系统的高分辨率数据却很少。在这项贡献中，我们研究了最近的原位中的微量元素以及硫，氮和有机碳稳定同位素的组成纳米比亚沿海的磷酸盐沉积物。此外，我们检查了磷沉积物中不同的广泛使用的地球化学代理的可靠性。我们的研究结果表明，从硫化状态转变为低氧状态，这与固体磷酸钙矿物质浓度的最大值相吻合。这种转变伴随着Mo和Re富集以及TOC丰度的单向变化。相对低的黄铁矿δ ^34个价值观磷酸盐沉积物（约-20‰）表示phosphogenesis期间开放系统分馏。phosphogenesis的启动也伴随着在沉积δ负位移¹³ Ç_有机和δ ¹⁵的N值。磷酸盐相关硫酸（PAS）δ ³⁴S值低于现代海水硫酸盐值，表明参与了化学营养型硫的氧化。我们的结果表明，氧化还原条件从硫化转变为（亚）氧化，再加上有效的硫循环是产生磷的先决条件。磷沉积物在U和V中显示出大量富集，突显了使用这些元素以及V /（V + Ni）和V / Cr作为氧化还原代理的复杂性，尤其是在磷矿和磷沉积物中。