Microbialites are formed through two processes, the trapping and binding of sediment grains and mineral precipitation. Sediment trapping and binding result in coarse sandy textures, whereas fine micritic textures are produced by mineral precipitation. Although well-studied modern microbialites (e.g. Bahamas and Shark Bay) are formed through the former process, purely trapped-and-bound examples are rare throughout the geologic record and limited to shallow-marine environments. Through the use of conventional microscopy and 3D micro-computed tomography (µ-CT) scanning, this study found that South African coastal microbialites have a primarily mineral precipitated texture, although detrital material is included sporadically. Furthermore, these modern microbialites exhibit both micritic and fibrous layering with high porosity. The novel use of 3D microtomography rotational scans has revealed that microbialites are extensively burrowed by metazoan activity and was also able to distinguish the occurrence and distribution of heavy minerals and detrital shell material in the samples. Some of the detrital grains appeared to be accidental/random inclusions, while in other cases the metazoan burrows provided space for the accumulation of sediment once abandoned. In both cases, sediment was incorporated as a product of intermittent accumulation, rather than systematic trapping and binding. The microfabric texture of South African microbialites is therefore a function of both biological (e.g. microbially mediated precipitation) and environmental (e.g. sporadic sediment deposition and inorganic cementation) influence. Overall, the findings presented here highlight the importance of these systems regarding microbialite formation, ichnology and taphonomy.

中文翻译：

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后生动物活动促进现代潮上微生物岩中的被动沉积物捕获：使用 μ-CT 扫描和显微镜揭示

微生物岩是通过两个过程形成的，沉积物颗粒的捕获和结合以及矿物沉淀。沉积物截留和结合导致粗糙的沙质质地，而精细的泥晶质地是由矿物沉淀产生的。尽管经过充分研究的现代微生物岩（例如巴哈马和鲨鱼湾）是通过前一个过程形成的，但在整个地质记录中，纯被困和束缚的例子很少见，并且仅限于浅海环境。通过使用传统显微镜和 3D 显微计算机断层扫描 (μ-CT) 扫描，该研究发现南非沿海微生物岩具有主要的矿物沉淀结构，尽管偶尔会包含碎屑材料。此外，这些现代微生物岩表现出具有高孔隙率的泥晶和纤维层状结构。3D 显微断层扫描旋转扫描的新用途表明，微生物岩被后生动物活动广泛挖掘，并且还能够区分样品中重矿物和碎屑壳材料的发生和分布。一些碎屑颗粒似乎是偶然/随机的包裹体，而在其他情况下，后生动物洞穴为曾经被遗弃的沉积物的积累提供了空间。在这两种情况下，沉积物都是作为间歇性积累的产物，而不是系统的捕获和结合的产物。因此，南非微生物岩的微结构是生物（例如微生物介导的降水）和环境（例如零星沉积物沉积和无机胶结）影响的函数。总体，