中国南方新元古代可能后生动物成因的硅化和磷酸盐化球状微化石Tianzhushania

Silicified and Phosphatized Tianzhushania , Spheroidal Microfossils of Possible Animal Origin from the Neoproterozoic Doushantuo Phosphorites of Guizhou,South China

对中国南方贵州瓮安地区上新元古界陡山沱组两种类型沉积:燧石夹层(切片法研究)和磷灰岩／含磷碳酸盐岩(切 片法和浸解法研究)中微化石的比较研究表明,磷酸盐化的Megasphaera ornata与燧石中保存的Tianzhushania tuberifera可 能代表由不同矿化过程保存下来的同一生物分类。磷酸盐化标本的外层壁经常脱落,而暴露其具纹饰的中间壁。在一些孤 立于围岩基质的磷酸盐化标本和在磷灰岩薄片所见到的标本上显现部分带刺的外壳保存,它们可以同燧石夹层薄片中发现 的化石进行比较。磷酸盐化标本的中间壁瘤突表面上普遍见到的凹坑,相当于外层壁刺饰所遗留下的附着点。而具有刺饰 的外层壁形态是Tianzhushania Yin and Li,1978属的典型特征,因此建议Tianzhushania ornate(Xiao等,2000)Yin et al., 2004为该种的有效名称。而主要依据其中间壁的纹饰形态所得出的该种为后生动物休眠卵的认识与目前结果并不矛盾。但 是,外层壁具刺饰的形态说明该种为浮游性的,而不是底栖性的生态类型。

Comparative study of microfossils from two kindsof sediments: chert intercalations (studied in thin section) and phospho-rite/phosphatic carbonate (in thin section and maceration), from the upper Neoproterozoic Doushantuo phosphorites in the Weng'an area, Guizhou Province, South China, shows that the phosphatized Megasphaera ornata Xiao and Knoll, 2000, and the chert-preserved Tianzhushania tuberifera Yin, Gao and Xing, 2001, should be regarded as representing the same taxon preserved by different mineralization processes. In phosphatized specimens the outer wall is often peeled off, exposing the ornamented middle wall. Some phosphatized specimens isolated from the rock matrix and specimens seen in thin sections of phosphorites show a partly preserved outer wall with spines, which can be compared to the thin-sectioned specimens from the chert beds. The small pits usually seen on the surface of the ornamented middle wall of phosphatized specimens correspond to the attachment spots of the spines in the outer wall. The presence of a spiny outer wall is a characteristic of Tianzhushania Yin and Li, 1978. Tianzhushania ornata (Xiao and Knoll, 2000) comb. nov. is here proposed as the valid name for the species. The proposed resting-egg nature of T. ornata, mainly based on the ornament type of the middle wall, cannot be excluded. The presence of a spiny outer wall, however, suggests that it is a pelagic rather than a benthic form.