Molybdenum Isotope Signatures from Yangtze Craton Continental Margin and Its Indication to Organic Burial Rate
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摘要: 通过对扬子克拉通古大陆边缘不同时期沉积岩的Mo同位素进行测定, 结合Mo微量元素组成, 对古大陆边缘Mo的自生作用规律进行了研究, 并根据Mo丰度对原始有机碳堆积速率进行了计算.结果表明, 其原始有机碳堆积速率在0.17~0.67mmol/m2/day之间.利用已建立的现代大陆边缘δ98Mo与有机碳埋藏速率模型, 对该区不同时期沉积岩的有机碳埋藏速率进行恢复.结果表明, 扬子克拉通显生宙不同时期沉积岩的有机碳埋藏速率有较大的变化范围(0.43~2.87mmol/m2/day), 并与原始有机碳堆积速率具有明显的相关性, 因此, δ98Mo有可能成为评价有效烃源岩的潜在指标.Abstract: The paper presents the molybdenum isotope data, along with the trace element content, to investigate the geochemical behavior of authigenic Mo during long-term burial in sediments in continental margin settings of Yangtze craton, as well as their indication to the burial of original organic carbon. The burial rate of original organic carbon was estimated on the basis of the amount of sedimentary sulphur (TS content), whilst the carbon loss by aerobic degradation was estimated according to calculated Mn contents. On these points, the original organic carbon flux was calculated, exhibiting a large range of variation (0.17-0.67 mmol/m2/day). The strong correlation between sedimentary Mo isotope values and organic carbon burial rates previously proposed on the basis of the investigations on modern ocean sediments, was also used here to estimate the organic carbon burial rate. The data gained through this model showed that organic carbon burial rates have large variations, ranging from 0.43-2.87 mmol/m2/day. Although the two sets of data gained through different geochemical records in the Yangtze craton show a deviation of one order of magnitude, they do display a strong correlation. It is thus tempting to speculate that the Mo isotope signature of sediments may serve as a tracer for the accumulation rate of original organic carbon in the continental margin sediments.
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图 1 扬子克拉通北缘西乡-碑坝地区取样地点示意图(据高山, 1989修改)
Fig. 1. Map of the study area showing the approximate locations of the investigated sites from the north margin of Yangzte craton
图 5 原始有机碳埋藏速率(Cflux) 与有机碳埋藏速率关系(Cburial)
Fig. 5. The original carbon burial rate (Cflux) plotted as a function of organic carbon burial rate (Cburial)
表 1 扬子克拉通北缘碎屑沉积岩Mo同位素和微量元素数据
Table 1. Mo isotope and trace element compositions of clastic sediments from the north margin of Yangtze craton
表 2 原始有机碳堆积速率(Cflux) 和有机碳埋藏速率(Cburial) 的计算结果
Table 2. The results of the original organic carbon burial rate (Cflux) and organic carbon burial rate (Cburial) from δ98Mo calculating model (Siebert et al., 2006)
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