The importance of organic-rich shales to the geochemical cycles of rhenium and osmium
The importance of organic-rich shales to the geochemical cycles of rhenium and osmium
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DOI：
10.1016/j.chemgeo.2015.03.010
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发表时间：
2015-05-18
期刊：
影响因子：
3.9
通讯作者：
Peucker-Ehrenbrink, Bernhard
中科院分区：
文献类型：
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作者：
Dubin, Andrea;Peucker-Ehrenbrink, Bernhard
海洋富有机物沉积物在表层锇和铼循环中所起的作用被认为是重要的，因为与平均大陆地壳相比，这些还原性沉积物中的Re/Os比高，这些元素的浓度也高。高Re/ o导致Os-187/Os-188比值迅速上升。我们通过编制地球化学数据库，量化富有机质沉积物的平均Re-187/Os-188和Os-187/Os-188比值，确定这些沉积物在地表锇和铼收支中的作用有多大。然后，我们利用不同时代地质记录中富有机质沉积物丰度的估计值来估计这些沉积物的平均Os-187/Os-188。研究发现，不同体积-年龄模型计算的富有机质沉积物的Os-187/Os-188值在2.22 ~ 2.27之间，误差估计分别为2.07 ~ 2.42和2.12 ~ 2.48。尽管这些沉积物在上大陆地壳中所占的比例相对较小，但由于这些元素的高浓度，它们对上大陆地壳铼的贡献不成比例地大（约50%），对锇的贡献较小（5-10%）。(C) 2015 Elsevier B.V.版权所有
The role that marine organic-rich sediments play in the surficial osmium and rhenium cycles has been assumed to be important due to the high Re/Os ratios and high concentrations of these elements in such reducing sediments compared to the average continental crust. The high Re/Os leads to rapidly increasing Os-187/Os-188 ratios. We determine how large a role these sediments play in the surficial osmium and rhenium budgets by compiling a geochemical database to quantify the mean Re-187/Os-188 and Os-187/Os-188 ratios of organic-rich sediments. We then utilize estimates of the abundance of organic-rich sediments in the geologic record of different ages to estimate an average Os-187/Os-188 for these sediments. We find that the calculated Os-187/Os-188 value of organic-rich sediments varies between 2.22 and 2.27 depending on the volume-agemodel used, with error estimates of 2.07 to 2.42 and 2.12 to 2.48, respectively. Despite the fact that these sediments constitute a relatively small proportion of the upper continental crust, they contribute a disproportionately large amount (>50%) to the upper continental crustal rhenium and, to a lesser extent (5-10%), osmium inventories owing to their high concentrations of these elements. (C) 2015 Elsevier B.V. All rights reserved.