Abstract Investigation of fault rocks is crucial for the evaluation of sealing properties of rock formations considered as oil and gas storage or for the disposal of heat-generating radioactive waste. Even in tight rock formations, fluid flow may concentrate along brittle faults. The present study focuses on the sealing properties of faulted Lower Cretaceous clay- and siltstones encountered in drill cores from the central and eastern Lower Saxony Basin (Germany). Our investigations are based on a multidisciplinary approach including microstructural, mineralogical-geochemical, stable isotope and biomarker analyses. The new data suggest that preexisting discontinuities and/or sedimentary heterogeneities played a significant role for the increase in fluid pressure and formation of mode I veins within low permeability claystones. High-strain domains of fault cores consist of fine-grained fault gouge. A scaly fabric of varying deformation intensity is present around larger faults. Calcite-precipitation in faults and complex mineralized veins, and the differences in trace element concentrations of various veins, reflect several phases of palaeofluid activity. Calcite precipitation in the fault rocks led to elevated amounts of Mn, Ba and/or Sr. Isotope signatures indicate a local carbonate source for the origin of thin calcite coatings of fault planes, but a more complex palaeofluid interaction for the larger faults and for complex veins, consistent with the microfabrics. Biomarker signatures reveal the presence of mature hydrocarbons pointing to hydrocarbon migration in sections where steep, only weakly mineralized faults occur. The new results suggest that faulted claystones represent critical zones with a potentially reduced barrier capability consistent with published data.

中文翻译：

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下白垩统粘土岩（德国北部下萨克森盆地）中流体控制的脆性断层和脉的结构、运动学和组成：来自岩相学研究、微结构、稳定同位素和生物标志物分析的限制

摘要 断层岩的研究对于评价被认为是油气储存的岩层的密封性能或处置发热放射性废物至关重要。即使在致密的岩层中，流体流动也可能沿着脆性断层聚集。目前的研究重点是在下萨克森盆地（德国）中部和东部的钻芯中遇到的断层下白垩统粘土和粉砂岩的封闭特性。我们的调查基于多学科方法，包括微观结构、矿物地球化学、稳定同位素和生物标志物分析。新数据表明，先前存在的不连续性和/或沉积非均质性对流体压力增加和低渗透粘土岩内 I 型脉的形成起到了重要作用。断层核心的高应变域由细粒度断层泥组成。较大断层周围存在变形强度不同的鳞片状结构。断层和复杂矿化脉中的方解石沉淀，以及各种脉中微量元素浓度的差异，反映了古流体活动的几个阶段。断层岩中的方解石沉淀导致 Mn、Ba 和/或 Sr 的含量升高。同位素特征表明断层面的薄方解石涂层起源的局部碳酸盐来源，但对于较大断层和复杂脉，与微织物一致。生物标志物特征揭示了成熟烃的存在，表明在发生陡峭、仅弱矿化断层的部分中烃迁移。