Spatial distribution of organic functional groups in Ediacaran acritarchs from the Doushantuo Formation in South China as revealed by micro-FTIR spectroscopy
Spatial distribution of organic functional groups in Ediacaran acritarchs from the Doushantuo Formation in South China as revealed by micro-FTIR spectroscopy
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DOI：
10.1016/j.precamres.2022.106628
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发表时间：
2022-03-10
影响因子：
3.8
通讯作者：
Takai, Ken
中科院分区：
文献类型：
--
作者：
Igisu, Motoko;Ueno, Yuichiro;Takai, Ken
利用拉曼光谱和傅里叶变换红外光谱技术，研究了中国地区埃迪卡拉纪(635~551 Ma)陡山沱组黑色硅质岩结核中有机质微体化石的化学特征及其空间分布。拉曼光谱参数(I-1350/1600值)表明，鞭毛、束丝和OM具有不同程度的结构有序性，而单个鞭毛的不同部分(即内部结构、内膜和外壁)的I-1350/1600值没有显著差异。红外图谱显示了个别甲藻标本中部分特定的化学特征。天祝山藻的内膜含有脂肪族C-H键。包括天柱山在内的方块石具四种内部结构：(1)富芳烃C-H型，(2)富脂型C-H型，(3)贫C-H型芳烃，或(4)非均质。无论有无突起，所有受检的目标生物都有富含C-H的芳香族外壁。这些特征支持真核生物的包囊起源，尽管很难确定原生动物或后生动物的包囊是否对应于原生动物的包囊。成束的细丝也由芳香族CH键组成，但其来源尚不清楚。OM的拉曼光谱I-1350/1600值变化很大，不对称脂肪族CH3/CH2的红外光谱强度比也是如此，同时芳香族和脂肪族C-H带的空间分布也不均匀。这表明来自死亡微生物细胞碎片和胞外有机化合物的各种前体的贡献。总体而言，这些结果证实了陡山坨微生物区系中存在各种微生物。此外，个体微体化石中有机官能团的空间分布可以为来源不明的微体化石的分类提供线索。
Raman and Fourier-transform infrared (FTIR) microspectroscopic analyses were performed to examine the chemical signatures and their spatial distribution of organic-walled microfossils together with organic matter (OM) in a black chert nodule from the Ediacaran (635-551 Ma) Doushantuo Formation in China. Raman spectral parameters (I-1350/1600 values) reveal that the acritarchs, bundled filaments, and OM have different degrees of structural order, and that there is no significant difference in I-1350/1600 values among the different portions of individual acritarchs (i.e., inner structure, inner membrane, and outer wall). The IR mapping reveals portionspecific chemical signatures within the individual acritarch specimens. The inner membrane of Tianzhushania contains aliphatic C-H bonds. The acritarchs, including Tianzhushania, show chemically four types of inner structures: (1) aromatic C-H-rich type, (2) aliphatic C-H-rich type, (3) aromatic/aliphatic C-H-poor type, or (4) heterogeneous. All of the examined acritarchs have aromatic C-H rich outer wall, irrespective of the presence/ absence of processes. These features support a eukaryotic cyst origin, although it is difficult to determine whether the acritarchs correspond to the cysts of Protista or Metazoa. The bundled filaments also consist of an aromatic CH bond, but its origin is uncertain. The OM shows a high degree of variation in Raman spectral I-1350/1600 values, as does the IR spectral intensity ratio of asymmetric aliphatic CH3/CH2, alongside a heterogeneous spatial distribution of aromatic and aliphatic C-H bands. This suggests the contribution of various precursors derived from dead microbial cell debris and extracellular organic compounds. Overall, these results confirm the presence of diverse microorganisms in the Doushantuo microbiota. Furthermore, the spatial distribution of organic functional groups in individual microfossils could provide clues about the taxonomy of microfossils of unknown origin.