In the Firth of Clyde area of southwest Scotland, the Famennian Kinnesswood Formation includes an interval of massive, host-replacing phreatic calcrete hardpan (HRPCH), the likes of which have been documented only at few locations and few intervals in geological history. The HRPCH is found only at basin-margin shoulders, where the Kinnesswood Formation succession is thin and incomplete. The isles of Bute and Great Cumbrae provide well exposed sections in which adjacent shoulder and trough successions can be correlated and compared to clarify the tectonostratigraphic and paleoenvironmental settings of the HRPCHs. In the Cumbraes Trough, above a thin interval of peritidal limestone, the middle part of the Kinnesswood Formation (lower part of the Foul Port Member) is pervasively disturbed by large syndepositional dewatering structures interpreted to be products of the intermittent deposition and dissolution of evaporites. These structures occur at approximately the same stratigraphic interval as the HRPCHs on the isles of Bute and possibly Arran. The HRPCH in Bute is interpreted to have developed on a syndepositional shoulder adjacent to a growth fault (the Kerrycroy Fault) delimiting a trough that accommodated intermittent seawater incursions in a restricted, evaporitic setting. This is consistent with the current model for HRPCH formation, which involves the mixing of fresh groundwater issued from source areas with the high pH groundwater that surrounds evaporitic basins. A significant increase in silica solubility paired with a decrease in calcite solubility occurs in the mixing zone, thus promoting the thorough replacement of silicates with calcrete.

中文翻译：

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苏格兰西南部上泥盆统 Kinnesswood 组盆地边缘发育的宿主置换潜水钙质硬质岩的构造地层和古环境背景

在苏格兰西南部的克莱德湾地区，法门尼期金内斯伍德组包括一段块状的、宿主替代的潜水钙质硬质岩（HRPCH），在地质历史上，仅在少数地点和少数间隔记录了类似的情况。HRPCH 仅在盆地边缘发现，Kinnesswood 组层序薄且不完整。Bute 岛和 Great Cumbrae 岛提供了良好的暴露剖面，在这些剖面中可以关联和比较相邻的台肩和槽序列，以阐明 HRPCH 的构造地层和古环境设置。在 Cumbraes Trough，在薄薄的围带石灰岩层段之上，Kinnesswood 组的中部（Foul Port 段的下部）普遍受到大型同沉积脱水结构的干扰，这些脱水结构被解释为蒸发岩间歇沉积和溶解的产物。这些构造与布特岛上的 HRPCHs 和可能的 Arran 上的地层间隔大致相同。布特的 HRPCH 被解释为是在与生长断层（Kerrycroy 断层）相邻的同沉积肩台上发育的，该断层界定了一个在受限制的蒸发环境中容纳间歇性海水侵入的槽。这与 HRPCH 形成的当前模型一致，该模型涉及从源区流出的新鲜地下水与蒸发盆地周围的高 pH 值地下水的混合。