蓝细菌死后, 容易受到降解作用的影响而腐烂, 难以保存为完好的化石。地史时期保存比较好的蓝细菌化石, 大都在一些特殊的如燧石等沉积岩中。在我国华南二叠纪–三叠纪之交广泛发育的微生物岩中, 真正意义上保存完整的蓝细菌化石较为少见, 大部分缺乏蓝细菌的内部结构, 往往只保存有蓝细菌的轮廓或铸模。 本文报道了四川省广安市谢家槽剖面夜郎组底部微生物岩中保存完整且内部存在拟似子细胞的单细胞 Stanieria-like 球状蓝细菌化石及其生态习性。这一发现表明 Stanieria-like 球状蓝细菌的钙化作用, 不仅发生在鞘上和鞘外，也发生在鞘内拟似子细胞上。Stanieria-like 球状蓝细菌化石的较好保存与该地区夜郎组底部的沉积环境(局限海台地)及其区域上有利的海洋地球化学环境如 CO₂ 分压以及海洋中碳酸盐高饱和度有关。 这一发现对于研究二叠纪–三叠纪之交该地区的海洋环境及海洋古生态都具有重要意义。谢家槽剖面微生物岩中不仅产有莓状黄铁矿, 还产有星点状、斑块状和条带状等其他各种不同形态的黄铁矿, 它们具有各自不同的成因过程。扫描电镜研究发现, 交代作用形成的斑块状和条带状黄铁矿常常为半球形集合体, 类似于围岩中的球状蓝细菌的外形, 推测为球状蓝细菌在黄铁矿化中产生的复制作用。本文首次报道了这一新的发现, 详细描述了各种黄铁矿的形态和结构特点, 并初步分析了它们的成因。

Cyanobacteria are hard to be well preserved as intact fossils through calcification because they easily suffer from microbial degradation after death. Sometimes, only calcified sheaths in some genera like Girvanella can be preserved in rocks. Most of the well-preserved cyanobacteria in geologic time are found in some special sedi-mentary rocks such as cherts. The coccoid cyanobacteria are rarely found as well-preserved fossils in microbialites that are widespread in South China. The expansion of cyanobacteria and the wide occurrence of microbialites are one of the features related to microbial communities in the aftermath of the Permian-Triassic mass extinction. Here in this paper, well preserved unicellular Stanieria-like coccoid cyanobacterial fossils are reported from the bottom of the Yelang Formation at the Xiejiacao section of Guang’an, Sichuan. These fossils are mainly composed of likely daughter cells and sheaths. The colonial structure of the Stanieria-like cyanobacteria is resulted from the type of re-production and the mucilaginous sheaths. Reproduction of the Stanieria-like coccoid cyanobacteria is characterized by simultaneous multiple fission (baeocytes division). The preservation of the Stanieria-like coccoid cyanobacterial fossils is ascribed to the special depositional environments of the Yelang Formation. These environments, including restricted marine platform, pressure level of atmospheric CO₂ and carbonate saturation state of seawater, enabled the calcification of the cyanobacteria. The discovery of these fossils is significant for us to understand the Permian-Triassic marine paleoenvironments and paleoecology. Pyrites in microbialites at the bottom of Yelang Formation have a variety of morphology including framboids, stellate, patchy and striated forms. SEM observations show that patchy and striated pyrites often have the appearances comparable to coccoid cyanobacteria. It can be inferred that they inherited their morphology from the coccoid cyanobacteria through pyritization.

国家自然科学基金(41772020)资助