Bullslaughter Bay in southern Pembrokeshire, UK, exposes sections of Upper Mississippian limestone strata. In many places, the rock suffered an isovolumetric alteration during a period of sea-level oscillations. We used multiple approaches to study the weathered rocks, combining sedimentological, petrographic and isotopic compositions (δ18O and δ13C values). Two main microfacies are recognized: (i) packstones/grainstones, characteristic of an open marine shallow subtidal/intertidal environment, with a high degree of agitation, slightly elevated salinity and temporary subaerial exposure; and (ii) mudstones/wackestones in a lagoonal setting and intertidal or supratidal environments, with a pedogenetic influence. In both cases, a complex diagenetic story, which started early in a meteoric environment, induced a strong alteration producing loose sediments in place of the parent rock. Calcretization, at or near the sediment surface in the vadose zone, was one of the most widespread diagenetic modes. It could be associated with beachrocks. Carbon and oxygen stable isotope analyses from more or less weathered limestones support the petrographic data: they show non-marine values with δ13C ranges of from −2.13 ‰ to 1.75 ‰ and δ18O from −6.05 ‰ to −4.66 ‰. These values are systematically lower than those of the middle Carboniferous seawater. Some periods of low sea level and subaerial exposure allowed gypsum to form. Neoformation of euhedral quartz by probable replacement after sulfate, and halite pseudomorphs after gypsum in a hypersaline environment are documented for the first time in southern Pembrokeshire. The studied weathered limestones present a complex diagenetic evolution related to sea-level oscillations in a range of hot and contrasting seasonal climates.

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彭布罗克郡南部（威尔士布尔斯劳特湾）的密西西比晚期石灰岩沉积环境：大气成岩作用和高盐度特征的证据

英国彭布罗克郡南部的布尔斯劳特湾暴露了上密西西比石灰岩地层的部分区域。在许多地方，岩石在海平面振荡期间发生了等容变化。我们使用多种方法来研究风化岩石，结合沉积学、岩相学和同位素组成（δ18O 和 δ13C 值）。识别出两种主要微相： (i) 泥灰岩/颗粒岩，具有开阔的海洋浅潮下/潮间带环境的特征，具有高度搅动、盐度略微升高和暂时的地下暴露；(ii) 泻湖环境和潮间带或潮上带环境中的泥岩/泥岩，具有成土影响。在这两种情况下，在大气环境早期开始的复杂成岩作用引发了强烈的蚀变，产生了松散的沉积物代替母岩。渗流带沉积物表面或其附近的钙化是最普遍的成岩模式之一。它可能与海滩岩石有关。来自或多或少风化石灰岩的碳和氧稳定同位素分析支持岩相学数据：它们显示非海洋值与 δ13C 范围从 -2.13 ‰ 到 1.75 ‰ 和 δ18O 从 -6.05 ‰ 到 -4.66 ‰。这些值系统地低于中石炭纪海水的值。某些时期的低海平面和地下暴露使石膏形成。在彭布罗克郡南部首次记录了在高盐环境中硫酸盐后可能替换自面体石英的新形成，以及石膏后的岩盐假形体。研究的风化石灰岩呈现出复杂的成岩演化过程，与一系列炎热和对比鲜明的季节性气候中的海平面振荡有关。