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Girvanella-coated grains from Cambrian oolitic limestone

机译：寒武纪硬质灰岩的Girvanella涂层谷物

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Oolites from the Cambrian carbonate sequences of China were analyzed using standard petrographic methods. Thin-section examination reveals that Girvanella, probably representing calcified sheath of a filamentous cyanobacterium, is well preserved in carbonate grains with little diagenetic alterations. The carbonate grains preserved with Girvanella may constitute an independent category here, since Girvanella was previously rarely known in carbonate grains, especially in ooids. According to the microstructures, these carbonate grains can be divided into two types: Girvanella oncoids are ooid-sized grains composed entirely of a meshwork of Girvanella coating a poorly defined nucleus; Girvanella ooids in samples can be further subdivided into two types, Girvanella-core ooids and Girvanella-cortex ooids, according to the microstructures and the distribution of Girvanella in the ooids. Girvanella-core ooids are characterized by a well-defined Girvanella nucleus, which was probably a rounded fragment of the former cyanobacterial buildup. Girvanella-cortex ooids, in contrast, are characterized by the alternations of Girvanella laminae and the micrite laminae. Observations of this study provide direct evidence that microbes, most likely cyanobacteria, were involved in the formation of coated carbonate grains and influenced their microstructures.
机译：使用标准的岩相学方法分析了中国寒武纪碳酸盐岩层序中的橄榄岩。薄层检查表明，长春花杆菌（可能代表丝状蓝细菌的钙化鞘）在碳酸盐颗粒中保存良好，几乎没有成岩作用。用长柄香草保存的碳酸盐颗粒在这里可能是一个独立的类别，因为长柄香草以前在碳酸盐颗粒中尤其是在阿片类中很少见。根据微观结构，这些碳酸盐颗粒可分为两种类型：长叶小肠长石样的类固醇颗粒大小完全由长满定义不清的核的长叶小肠网组成。样品中的小叶长颈鹿阿片类物质可根据其微结构和分布情况进一步细分为两类，即长叶小黑猩猩核心类阿片类和长叶小戈尔皮质类阿片类。 Girvanella核心类oid的特征是Gilvanella核的轮廓清晰，这可能是以前的蓝细菌堆积的圆形片段。相比之下，Girvanella-皮质皮质激素的特征是薄片状的Girvanella laminae和薄片状的micrite。这项研究的观察结果提供了直接证据，表明微生物（最可能是蓝细菌）参与了包覆碳酸盐颗粒的形成并影响了其微观结构。

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