Reconstruction of the geological history of orogenic events can be challenging where basins have limited and/or fragmentary preservation. Here, we apply understanding gained from modern analogues to the sedimentological analysis of the succession of Upper Silurian to Lower Devonian Lower Old Red Sandstone (LORS), northern Midland Valley, Scotland, in order to reconstruct the foreland to the Caledonian orogeny. A new depositional model is presented which differs significantly from current understanding. Using facies analysis, grain size distribution and palaeocurrent data a large distributive fluvial system is reconstructed. Three lithofacies and nine sublithofacies are identified, forming fluvial channel and floodplain facies associations. The system was derived from an emerging mountain range in the Caledonian foreland undergoing constant tectonic rejuvenation to produce 9 km of coarse‐grained sediment, exhibiting an overall decrease in thickness towards the west and a large‐scale downstream reduction in grain size. Conglomerate sublithofacies dominate proximal areas in the east where amalgamated fluvial channel facies association is abundant, with a downstream increase in the dominance of floodplain facies. Additionally, observed grain size cyclicity is attributed to a pulsatory tectonic influence. The LORS records the time‐period between the late phases of the Caledonian Orogeny and the onset of post‐orogenic collapse in the mid‐Devonian and the presented model allows improved understanding of the north‐Atlantic Caledonian foreland.

中文翻译：

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加里东前陆盆地沉积：苏格兰米德兰谷盆地志留系-下泥盆统下老红砂岩的新沉积模型

在盆地保存有限和/或片断化的地区，重建造山活动的地质历史可能会面临挑战。在这里，我们将从现代类似物中获得的理解应用于对苏格兰上米德兰河谷北部志留纪-下泥盆统下老红砂岩（LORS）演替的沉积学分析，以重建前陆至加里东造山带。提出了一种新的沉积模型，该模型与当前的理解有很大不同。使用相分析，粒度分布和古流数据，重建了一个大型的分布式河流系统。确定了三个岩相和九个亚岩相，形成了河道和洪泛区相联系。该系统来自加里东前陆的一个新兴山脉，该山脉经过不断的构造复兴，产生了9 km的粗粒沉积物，向西厚度总体减小，下游粒度大幅度减小。砾岩亚岩相在东部近端地区占主导地位，该地区的河道相结合非常丰富，下游的洪泛区相占主导地位。另外，观察到的晶粒尺寸的周期性归因于脉动构造的影响。LORS记录了加里东造山运动后期到中德文统中的造山后崩塌发生之间的时间周期，并且该模型可以更好地了解北大西洋加里东前陆。