Exceptional preservation of fossil plant spores in high-pressure metamorphic rocks
Exceptional preservation of fossil plant spores in high-pressure metamorphic rocks
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DOI：
10.1016/j.epsl.2007.07.041
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发表时间：
2007-10-15
影响因子：
5.3
通讯作者：
Goffe, Bruno
中科院分区：
文献类型：
--
作者：
Bernard, Sylvain;Benzerara, Karim;Goffe, Bruno
人们普遍认为，高级变质作用会抹去岩石中所有化石的痕迹，更广泛地说，会抹去岩石中的生物起源。为了解决这个问题，我们在这项研究中报道了在法国阿尔卑斯山三叠纪变质沉积岩中发现的纳米尺度的石蒜化石大孢子的X射线光谱、拉曼光谱和电子显微镜观察。这些岩石在阿尔卑斯山造山期间经历了高压变质条件(类似于14Kbar，类似于360℃)，对应于俯冲期间类似3.5公里的埋藏。尽管发生了这样的变质作用，但化石大孢子在结构上保存得非常完好。孢子壁结构上叠加了由磁铁矿、铁白铁矿和方解石组成的不寻常的矿物分带。同时，检测到组成孢子壁的有机物(OM)的化学不均一性。我们讨论了对我们的观察结果的不同解释，特别是这些特征是孢子中原始结构不均一性的残留物的情景，并对高级变质条件下的石化过程提供了见解。无论是什么过程导致了这种非均质性，我们的观察结果都与通常的假设相反，即高级变质作用抹去了岩石中所有生物成因的迹象，并为在成岩和变质作用期间有机质演化的纳米尺度上的研究开辟了新的途径。(C)2007 Elsevier B.V.保留所有权利。
It is commonly believed that high-grade metamorphism erases all traces of fossils and, more generally, of biogenicity in rocks. To address this issue, we report in this study X-ray spectromicroscopy, Raman microspectroscopy, and electron microscopy observations at the nm-scale of fossil lycophytes megaspores found in Triassic metasedimentary rocks from the French Alps. These rocks have undergone high-pressure metamorphic conditions (similar to 14 kbar, similar to 3 60 degrees C) during the Alpine orogeny corresponding to a burial of similar to 3 5 km during subduction. Despite such metamorphism, the fossil megaspores are remarkably well-preserved texturally. An unusual mineralogical zonation consisting of magnetite, ankerite and calcite is superposed on the structures of the spore walls. In parallel, chemical heterogeneities of the organic matter (OM) composing the spore walls were detected. We discuss different interpretations for our observations, in particular a scenario in which these features are remnants of the original structural heterogeneities in the spores, and provide insights on the fossilization processes under high-grade metamorphic conditions. Whatever the processes leading to such heterogeneities, our observations oppose the usual assumption that high-grade metamorphism erases all indications of biogenicity in rocks and open new avenues for investigation at the nm-scale of the evolution of organic matter during diagenesis and metamorphism. (c) 2007 Elsevier B.V. All rights reserved.