Abstract Two carbonate- and phosphate-rich concretions from Early Jurassic strata at Buttenheim (Bavaria, Germany) and their immediate claystone host rocks were analysed to study the mechanisms of biomarker preservation in concretions. Superimposed on a common sedimentary background signal, distinctive biomarkers reflect microbial processes involved in concretion formation. When normalized to the HCl-insoluble insoluble rock portion, concretions show ∼1.5–3 times higher TOC values than their host rocks, but identical absolute quantities of most extractable hydrocarbons. In contrast, n-fatty acids and α,ω-dicarboxylic acids are, by an order, more abundant compared to the host rocks, suggesting an enhanced preservation or selective accumulation mechanism for carboxylic acids in the concretions. Further, linear and iso-/anteiso-fatty acids with unusually short carbon chains (as low as C8) are exclusively observed in the concretions and are interpreted as biodegradation products of lipids derived from in-situ bacteria. Likewise, strongly enhanced neohop-13(18)-enes and hopanoic acids with more ‘immature’ isomer distributions indicate an in-situ contribution of microbial biomass during formation of the concretions. Pyrolysis released ample additional saturated short-chain n-fatty acids from the kerogens of the concretions, but not from the host rocks. We hypothesize that these compounds are remnants of locally accumulated OM rich in fatty acyl moieties (e.g. plant polymers or triglyceride storage lipids) whose hydrolysis products were initially precipitated as fatty acid salts (‘adipocere’). During shallow burial, these substances may have delivered a steadily flowing energy source for sedimentary microorganisms, with their anaerobic decomposition supplying both carbonate and metal ions. In concert with other factors, this may have promoted carbonate precipitation and thus, the formation of the Buttenheim concretions.

中文翻译：

---

两个早侏罗世结核及其直接寄主岩（Lias δ，Buttenheim 粘土坑，德国巴伐利亚）中的脂肪酸和其他生物标志物

摘要 分析了来自 Buttenheim（德国巴伐利亚）早侏罗世地层的两个富含碳酸盐和磷酸盐的结核及其直接粘土岩主岩，以研究结核中生物标志物的保存机制。叠加在共同的沉积背景信号上，独特的生物标志物反映了参与结核形成的微生物过程。当归一化为不溶于 HCl 的不溶性岩石部分时，结核的 TOC 值比其母岩高约 1.5-3 倍，但大多数可提取碳氢化合物的绝对数量相同。相比之下，n-脂肪酸和α,ω-二羧酸在一定程度上比主岩更丰富，这表明结核中羧酸的保存或选择性积累机制增强。更多，具有异常短碳链（低至 C8）的线性和异/反异脂肪酸仅在结核中观察到，并被解释为来自原位细菌的脂质的生物降解产物。同样，强烈增强的neohop-13(18)-enes 和具有更多“未成熟”异构体分布的hopanoic 酸表明微生物生物质在结核形成过程中的原位贡献。热解从结核的干酪根中释放了大量额外的饱和短链正脂肪酸，但没有从主岩中释放出来。我们假设这些化合物是局部积累的富含脂肪酰基部分（例如植物聚合物或甘油三酯储存脂质）的 OM 的残余物，其水解产物最初以脂肪酸盐（'adipocere'）的形式沉淀。浅埋时，这些物质可能为沉积微生物提供了稳定流动的能源，它们的厌氧分解提供了碳酸盐和金属离子。与其他因素一起，这可能促进了碳酸盐沉淀，从而促进了 Buttenheim 结核的形成。