The siliciclastic ~1 Ga‐old strata of the Torridon Group, Scotland, contain some of the most exquisitely preserved three‐dimensional organic‐walled microfossils (OWMs) of the Precambrian. A very diverse microfossil assemblage is hosted in a dominantly phosphatic and clay mineral matrix, within the Diabaig and the Cailleach Head (CH) Formations. In this study, we report on several microfossil taxa within the CH Formation (Leiosphaeridia minutissima, Leiosphaeridia crassa, Synsphaeridium spp. and Myxococcoides spp.) that include populations of cells containing an optically transparent and highly refringent mineral, here identified using electron microscopy as anatase (TiO₂). Most anatase crystals occur entirely within individual cells, surrounded by unbroken carbonaceous walls. Rarely, an anatase crystal may protrude outside a cell, interpreted to correspond to zones where the cell wall had broken down prior to anatase precipitation. Where an anatase crystal entombs an organic intracellular inclusion (ICI), the ICI is large and well preserved. These combined observations indicate that the intracellular anatase is an authigenic sedimentary phase, making this the first report of in situ precipitated anatase intimately associated with microfossils. The ability of anatase to preserve relatively large volumes of intracellular and cell wall organic material in these cells suggests that the crystallisation of anatase entombed cellular contents particularly quickly, soon after the death of the cell. This is consistent with the strong affinity of Ti for organic material, the low solubility of TiO₂, and reports of Ti occurring in living organisms. With the data currently available, we propose a mineralisation pathway for anatase involving Ti complexation with organic ligands within specific cells, leading to localised post‐mortem anatase nucleation inside these cells as the complexes broke down. Further overgrowth of the anatase crystals was likely fuelled by very early diagenetic mobilisation of Ti that had been bound to more labile organic material nearby in the sediments.

中文翻译：

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10亿年历史的细胞内有自生锐钛矿

苏格兰Torridon组的硅质碎屑〜1 Ga老地层包含一些前寒武纪保存最完好的三维有机壁微化石（OWM）。在Diabaig和Cailleach Head（CH）地层中，以磷和粘土为主的矿物基质中存在着多种多样的微化石组合。在这项研究中，我们报告了CH组内的几种微化石类群（Leiosphaeridia minutissima，Leiosphaeridia crassa，Synsphaeridium spp。和Myxococcoides spp。），其中包括含有光学透明和高反射性矿物的细胞群，这里使用电子显微镜将其鉴定为锐钛矿（二氧化钛₂）。大多数锐钛矿晶体完全存在于单个细胞中，周围是完整的碳质壁。锐钛矿晶体很少会突出到细胞外部，解释为对应于锐钛矿沉淀之前细胞壁已破裂的区域。锐钛矿晶体包裹有机细胞内包裹体（ICI）时，ICI很大且保存完好。这些综合的观察结果表明，胞内锐钛矿是自生沉积阶段，这是与微化石密切相关的原位沉淀锐钛矿的首次报道。锐钛矿在这些细胞中保留相对大量的细胞内和细胞壁有机物质的能力表明，锐钛矿的结晶在细胞死亡后很快特别迅速地吞噬了细胞内含物。参见图₂，并且报道了在生物体中发生Ti。利用目前可获得的数据，我们提出了一种锐钛矿的矿化途径，其中涉及与特定细胞内的有机配体进行Ti络合的Ti，随着复合物的分解，导致这些细胞内的局部死后锐钛矿成核。钛的早期成岩动员可能进一步促进了锐钛矿晶体的过度生长，而钛的成岩动员与沉积物中附近的较不稳定的有机物质结合。