In black shale studies, apparent lack of bioturbation is commonly taken as an indication of anoxic bottom waters. Yet, modern oxygen-stressed environments show that even at suboxic levels (0.0 to 0.2 ml l⁻¹ oxygen), microscopic eukaryotic benthic organisms live in the uppermost millimetres to centimetres of the substrate. Known as meiofauna, these organisms disturb the primary fabric as they move through the sediment. These modern examples inspired students of the rock record to report sub-millimetre irregular–wiggly features in black shale thin sections as meiofaunal burrows. Preparation flaws in thin section manufacture can cause reduced light transmission that results in darkened regions when viewed in transmitted light, and one wonders whether micro-burrows reported in the literature are indeed burrows, or alternatively artifact-induced optical illusions. Examining shale thin sections of Archean to Tertiary age showed: (i) that burrow-like features are common regardless of age; and (ii) that burrow identification varies significantly between observers. When transposing locations of presumed traces onto scanning electron microscope images of the same field of view (diamond polished surface), no evidence of fabric modification at locations of presumed burrows was observed. Microfabric within and outside ‘burrows’ was the same, and larger fabric elements traversed ‘burrows’ uninterrupted. Once both sides of the rock slice were polished, presumed burrows could no longer be observed, indicating that damage to the underside of the thin section caused the mistaken identification of micro-burrows. Because burrows emplaced in water-rich muds must undergo substantial compaction-induced ‘flattening’ and deformation prior to lithification, geometries of presumed burrows that disagree with a plausible compaction regime provide an additional filter to separate potential burrows from artifact-induced features. Recognizing meiofaunal disruption is an important aspect for accurate palaeoenvironmental interpretation of black shales. Yet, initial assessment via optical microscopy needs to be verified through scanning electron microscope-based examination of shale fabrics.

中文翻译：

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黑色页岩中的隐秘洞穴痕迹——岩相罗夏测试还是真实的东西？

在黑色页岩研究中，明显缺乏生物扰动通常被视为底水缺氧的迹象。然而，现代氧气压力环境表明，即使在低氧水平（0.0 至 0.2 ml l ^-1氧），微小的真核底栖生物生活在最上面几毫米到几厘米的基质中。这些被称为小型动物的生物在穿过沉积物时会扰乱主要结构。这些现代例子启发了岩石记录的学生将黑色页岩薄片中亚毫米的不规则摆动特征报告为小型动物洞穴。薄切片制造中的制备缺陷会导致透光率降低，在透射光下观察时会导致区域变暗，人们想知道文献中报道的微洞穴是否确实是洞穴，或者是人工制品引起的视错觉。检查太古代至第三纪的页岩薄片表明：（i）无论年龄如何，洞穴状特征都很常见；(ii) 洞穴识别在观察者之间存在显着差异。当将假定痕迹的位置转换到相同视场（金刚石抛光表面）的扫描电子显微镜图像上时，没有观察到假定洞穴位置处织物改性的证据。“洞穴”内部和外部的超细织物是相同的，较大的织物元素不间断地穿过“洞穴”。将岩片两侧磨光后，再观察不到推测的洞穴，说明薄片下侧的损伤导致了微洞穴的错误识别。因为位于富含水的泥浆中的洞穴在岩化之前必须经历大量的压实引起的“扁平化”和变形，与合理压实机制不一致的假定洞穴的几何形状提供了额外的过滤器，以将潜在的洞穴与人工制品引起的特征分开。识别小型动物群的破坏是准确解释黑色页岩古环境的一个重要方面。然而，需要通过基于扫描电子显微镜的页岩织物检查来验证通过光学显微镜进行的初步评估。