Diagenetic mobilization of Ti and formation of brookite/anatase in early Cambrian black shales, South China
Diagenetic mobilization of Ti and formation of brookite/anatase in early Cambrian black shales, South China
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华南早寒武世黑色页岩中钛的成岩活化与板钛矿/锐钛矿的形成
DOI：
10.1016/j.chemgeo.2018.12.022
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发表时间：
2019-02
期刊：
影响因子：
3.9
通讯作者：
Gao Jian-Feng
中科院分区：
文献类型：
--
作者：
Liu Ze-Rui Ray;Zhou Mei-Fu;Wiliams-Jones A.E;Wang Wei;Gao Jian-Feng
钛（Ti）通常存在于海洋沉积物中的碎屑矿物中，长期以来一直被认为在成岩作用期间是不活动的。在华南早寒武世梅树村剖面和渣金剖面的碳质页岩中，分别发现了板钛矿和钛铁矿这两种自生钛矿物。梅树村剖面黑色页岩的总有机碳（TOC）含量为1.6~3.9 wt %，氢指数（HI）值为3.8~20 mg HC/g TOC，而扎津剖面黑色页岩的TOC值高得多（7.1-15.6 wt %），但氢指数较低（<2.0 mg HC/g TOC），并含有丰富的沥青（~3 vol %）。梅树村剖面黑色页岩中的板钛矿总是沿着碎屑黑云母劈理结晶。这种密切的关联表明，钛形成二氧化钛矿物所需的是来自碎屑黑云母和钛动员只有在纳米到微米尺度。相反，扎金段黑色页岩中的沥青质骨料与沥青共生。有人建议，钛在这些页岩中动员在低pH值的有机丰富的流体，随后，优先沉淀为随pH值的增加而增加。惰性钛在黑色页岩中的动员是一个可能的成岩或成岩后元素在碳质岩石中的再分配的指示。研究结果进一步表明，基于黑色页岩地球化学成分的代用指标可以用于估算古海洋的氧化还原状态，但应谨慎使用。
Titanium (Ti) is typically hosted in detrital minerals in marine sediments and has long been considered to be immobile during diagenesis. In this study, the authigenic titania minerals, brookite and anatase, are observed in early Cambrian carbonaceous shales from the Meishucun and Zhajin sections of South China, respectively. Black shales in the Meishucun section have total organic carbon (TOC) contents from 1.6 to 3.9 wt% and HI (hydrogen index) values from 3.8 to 20 mg HC/g TOC, whereas black shales in the Zhajin section have much higher TOC (7.1–15.6 wt%) but lower HI (<2.0 mg HC/g TOC) and contain abundant bitumen (~3 vol%). Brookite in black shales from the Meishucun section crystallized invariably along cleavages of detrital biotite. This intimate association suggests that the Ti required to form titania minerals was derived from detrital biotite and that Ti was mobilized only on a nano- to micro-meter scale. In contrast, anatase aggregates in black shales from the Zhajin section are intergrown with bitumen. It is proposed that Ti in these shales was mobilized in low pH organic-rich fluids and, subsequently, preferentially precipitated as anatase with increasing pH. The mobilization of inert Ti in black shales is indicative of a possible diagenetic or post-diagenetic elemental redistribution in carbonaceous rocks. Our study further demonstrates that proxies based on geochemical component of black shales can be employed to estimate redox state of ancient oceans, but must be applied with caution.
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影响因子：
0.8
作者：
Hong‐fu Zhang;M. Sun;F. Lu;Xin-hua Zhou;Mei‐Fu Zhou;Yongshun Liu;Guohui Zhang
通讯作者：
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通讯作者：
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影响因子：
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作者：
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通讯作者：
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影响因子：
1.4
作者：
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通讯作者：
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