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首页> 外文期刊>Sedimentology: Journal of the International Association of Sedimentologists >Formation, diagenesis and palaeoenvironmental significance of upper Ediacaran fibrous dolomite cements
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Formation, diagenesis and palaeoenvironmental significance of upper Ediacaran fibrous dolomite cements

机译：上埃德拉甘松纤维白云岩水泥的形成，成岩作用和古环境意义

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摘要

Neoproterozoic marine dolomite cements represent reliable, albeit complex, archives of their palaeoenvironment. Petrological and high-resolution geochemical data from well-preserved fibrous dolomite and pyrite in the upper Ediacaran (ca 551 center dot 1 to 548 center dot 0 Ma) Dengying Formation in south-west China are presented and discussed here. The aim of this research is to reconstruct the redox state of late Ediacaran shallow seawater and porewater in the Sichuan Basin using early marine diagenetic fabrics. Based on crystalline texture and axis, four basic types of fibrous dolomite cements formed penecontemporaneously in a microbialite reef setting at the platform margin: (i) bladed dolomites (replacement from a high-Mg calcite precursor); (ii) fascicular fast dolomites (replacement from an aragonitic precursor); (iii) fascicular slow dolomites; and (iv) radial slow dolomites. The latter two fabrics are considered direct marine porewater precipitates due to their length-slow character, cathodoluminescent zonation, and enriched copper and cobalt concentrations. Marine cements yield rare earth element and yttrium patterns comparable to modern seawater and represent a refined set of archive data relative to previously published bulk dolostones. Redox-sensitive elements and cathodoluminescence indicate that the fascicular fast dolomites formed in suboxic seawater, while fascicular slow and radial slow dolomites formed in euxinic marine porewaters. Microbial sulphate reduction during the formation of fascicular slow and radial slow dolomites is recognized by nanometre-scale spheroidal ankerite and sulphur-containing dolomite, and intergrown pyrite grains with U-shaped delta S-34 transects. Data shown here suggest predominantly suboxic shallow late Ediacaran seawater and euxinic marine porewaters, with microbial activity promoting the direct precipitation of dolomite.
机译：NeoproteroZoice海洋白云石水泥代表可靠，虽然复杂，古代环境档案。在这里，在中国西南部的上埃德拉甘中保存纤维状白云石和黄铁矿中的岩石和高分辨率地球化学数据和纤维植物（CA 551中心点1至548个中心点0 mA）。该研究的目的是使用早期海洋型成岩织物重建四川盆地晚埃德加伦浅海水和沉皮水的氧化还原状态。基于结晶纹理和轴，在平台边缘的微生物卷礁设置中，四种基本类型的纤维白云岩水泥在平台边缘的微生物卷中形成：（i）叶片白云岩（替代高镁棉材前体）; （ii）瘘状快速白云岩（替代金属前体）; （iii）坐着的慢性白云岩; （iv）径向缓慢的白云岩。由于其长度慢的性质，阴极发光区分和富集的铜和钴浓度，后两种织物被认为是直接海洋沉淀物沉淀物。海洋水泥产生稀土元素和与现代海水相当的钇图案，相对于先前发表的散装天花板代表了一套精致的档案数据。氧化还原元素和阴极致发光表明，在中草水中形成的瘘状快速白云岩，而在迅速的海洋芯片中形成的坐着肌肉缓慢和径向缓慢的白云岩。在形成瘘管缓慢和径向缓慢的白云岩期间的微生物硫酸盐降低由纳米级球形脂肪酸和含硫的白云石识别，并具有U形ΔS-34横切的白天硫铁矿晶粒。这里显示的数据表明，主要是对埃德氏埃德拉兰海水和养殖海洋芯片的微生物活性，促进白云石的直接沉淀。

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