Abstract The Boda Claystone Formation, a potential host rock for high-level nuclear waste in Hungary, contains numerous sigmoidal vein arrays with angular vein terminations. These veins are excellent strain markers and can be used in the interpretation of palaeo-environments. Sigmoidal vein arrays were investigated in the BAF-2 well, which penetrates the formation to depths above 900 m with nearly 100% core recovery. The veins have antitaxial growth morphologies and are filled by calcite, anhydrite and barite–celestine phases. To estimate the volume change in shear zones, we used geometric, mass-balance and density-change calculations. These methods exhibit different volume loss rates. The geometric approach indicates a large amount of volume loss, whereas the isocon method and density-change approach suggest that volume loss in the shear zones was less than 10%. We propose that the volume loss in the shear zone occurred because of tectonic compaction. Vein shapes indicate formation under compressional stress fields. Based on their intersections with other vein generations, the sigmoidal en echelon vein generation is determined to be one of the youngest structures in the well, which probably formed during a Late Cretaceous compression event.

中文翻译：

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与博达粘土岩中 S 形脉阵列相关的剪切应变和体积变化

摘要 Boda 粘土岩组是匈牙利高放核废料的潜在母岩，包含许多具有角状脉终止的 S 形脉阵列。这些静脉是极好的应变标记，可用于解释古环境。在 BAF-2 井中研究了 Sigmoidal 脉阵列，其穿透地层深度超过 900 m，岩心采收率接近 100%。脉具有抗轴生长形态，被方解石、硬石膏和重晶石-天青石相填充。为了估计剪切带中的体积变化，我们使用了几何、质量平衡和密度变化计算。这些方法表现出不同的体积损失率。几何方法表明大量的体积损失，而 isocon 方法和密度变化方法表明剪切带中的体积损失小于 10%。我们认为剪切带中的体积损失是由于构造压实而发生的。静脉形状表示在压缩应力场下的形成。基于它们与其他脉代的交集，S 形梯状脉生成被确定为井中最年轻的构造之一，可能形成于晚白垩世压缩事件。