Comparison of reductive accumulation of Re and Os in seawater-sediment systems

采用多示踪技术和XAFS光谱对海水-沉积物体系中Re、Os的去除行为和去除过程中Re/Os的分异进行了研究。随着还原条件的发展，铼和氧可以从人工海水中被去除到沉积物中，证实了还原去除是Re和Os的重要过程。在氧化条件下，海水中的Os被去除到燃烧沉积物和无有机物沉积物中，而Re在相同条件下没有被去除到沉积物中。Os的去除过程似乎受几个因素的控制，如还原、水解和有机络合。虽然在我们的实验中，Re只有在高还原性条件下才被去除到沉积物中，但由于Re还原的缓慢动力学，在实验的时间尺度内无法观察到低还原性条件下的Re去除。因此，我们在此得出结论，Re对沉积物的去除需要还原条件，而Os在我们的实验中即使在氧化条件下也可以去除。因此，较高的^<187>Re/^<188>Os比值有利于还原沉积，如黑色页岩。高^<187>的Re/^<188>的Os比值使黑色页岩适合Re-Os定年，因为高^<187>的Re/^<188>的Os大量增长。而氧环境下的自生沉积物（和矿物）只能富集Os，导致Re/ Os比值远低于海水。这些材料的锇同位素系统的^<187>Os/^<188>Os比由于其^<187>Re/^<188>Os比极低而不能显著增长，因此可以用作古海洋环境示踪剂。

The removal behaviors of Re and Os in a seawater-sediment system and Re/Os fractionation during removal were studied by performing laboratory experiments using a multitracer technique and XAFS spectroscopy.1. Rhenium and Os can be removed from artificial seawater to sediments with development of reducing conditions, confirming that reductive removal is an important process for Re and Os. The removal of Os from the seawater to burnt sediment and organic-free sediment under oxic conditions was also observed, while Re was not removed from the seawater to the sediments under the same conditions. The removal process of Os seems to be controlled by several factors, such as reduction, hydrolysis, and orgaic complexation.2. Although Re is removed to sediments only under highly reducing condition in our experiments, the slow kinetics of Re reduction can inhibit the observation of Re removal under less reducing condition within the timescale of the experiments. Hence, we here conclude that reduction condition is needed for the removal of Re to sediments, while Os can be removed even under oxic condition as shown in our experiments. Thus, a high ^<187>Re/^<188>Os ratio can our in reducing sediments, such as black shale. The high ^<187>Re/^<188>Os ratio makes black shale suitable for Re-Os dating due to the large growth of high ^<187>Re/^<188>Os. In contrast, authigenic sediments (and minerals) under oxic environments can only enrich Os, which cause a much lower ^<187>Re/^<188>Os ratio than that of seawater. The osmium isotopic system of these materials can be used as a paleo-marine environmental tracer because the ^<187>Os/^<188>Os ratio cannot grow significantly due to its extremely low ^<187>Re/^<188>Os ratio.