Rockfalls are relatively little described from the ancient geological record, likely due to their poor preservation potential. At Clachtoll, northwest Scotland, a megaclast (100 m × 60 m × 15 m) of Neoarchean Lewisian gneiss with an estimated mass of 243 kt is associated with basal breccias of the Mesoproterozoic Stoer Group. Foliation in the megablock is misoriented by ∼90° about a subvertical axis relative to that in the underlying basement gneisses, and it is cut by fracture networks filled with Stoer Group red sandstone. Bedded clastic fissure fills on top of the megablock preserve way-up criteria consistent with passive deposition during burial. Sediment-filled fractures on the lateral flanks and base show characteristics consistent with forceful injection. Using numerical calculations, we propose that rift-related seismic shaking caused the megablock to fall no more than 15 m onto unconsolidated wet sediment. On impact, overpressure and liquefaction of the water-laden sands below the basement block were sufficient to cause hydrofracturing and upward sediment slurry injection. In addition, asymmetrically distributed structures record internal deformation of the megablock as it slowed and came to rest. The megablock is unrelated to the younger Stac Fada impact event, and represents one of the oldest known terrestrial rockfall features on Earth.

中文翻译：

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更大的摔伤：苏格兰西北部1.2岁大的陆地巨碎石的灾难性地质

古代地质记录对岩崩的描述相对较少，这可能是由于其潜在的保存潜力。在苏格兰西北部的克拉奇托尔（Clachtoll），新中古宙斯路易斯片麻岩的巨裂（100 m×60 m×15 m），估计重达243 kt，与中生代斯托尔群的基底角砾岩有关。相对于下伏的基底片麻岩而言，大块体中的叶相对于一个垂直下轴错位了约90°，并且被充满Stoer Group红砂岩的裂缝网络所切割。巨块顶部的层状碎屑裂隙填充物保持了与埋葬期间的被动沉积相一致的上升标准。侧面和底部的沉积物充满裂缝，表现出与强力注入一致的特征。使用数值计算 我们提出，与裂谷有关的地震震动导致大块体坠落到未固结的湿沙上的距离不超过15 m。撞击时，地下室下方的含水砂的超压和液化足以引起水力压裂和向上注入泥浆。此外，不对称分布的结构记录了大块体减速并静止时的内部变形。这个巨型区块与年轻的Stac Fada撞击事件无关，它代表了地球上最古老的地面落石特征之一。不对称分布的结构记录了大块减速并停止时的内部变形。这个巨型区块与年轻的Stac Fada撞击事件无关，它代表了地球上最古老的地面落石特征之一。不对称分布的结构记录了大块减速并停止时的内部变形。这个巨型区块与年轻的Stac Fada撞击事件无关，它代表了地球上最古老的地面落石特征之一。