The Ballagan Formation of northern Britain provides an exceptional record of Early Mississippian ecosystems that developed as tetrapods emerged onto land. In this paper, we study two 500-metre sections of the formation near Berwick-upon-Tweed, which are characterised by abundant ferroan dolostone beds. Five lithofacies are identified: cemented siltstone and sandstone, homogeneous dolomicrite, mixed dolomite and siltstone, mixed calcite and dolomite, and dolomite with evaporite minerals. Cemented sediments have non-planar to planar subhedral dolomite crystals, up to 40 μm in size, whereas other facies predominantly comprise dolomicrite or planar euhedral dolomite rhombs 15 μm in size, with patches of larger rhombs indicating partial recrystallisation. The macro- and microfossil content of the dolostones is dominated by sarcopterygian (rhizodont) and actinopterygian fish, bivalves, Serpula, ostracods and Chondrites trace fossils; with rarer Spirorbis, chondrichthyans (Ageleodus, hybodonts and ?ctenacanths, xenacanths), non-gyracanth acanthodians, gastropods, eurypterids, brachiopods, plant debris, wood, lycopsid roots, charcoal, megaspores, phycosiphoniform burrows, Zoophycos? and Rhizocorallium. The oxygen and carbon isotope composition of dolomites range from –3.6‰ to –1.7‰ (for δ¹⁸O) and –2.6‰ to +1.6‰ (for δ¹³C) respectively indicating dolomite growth in mixed salinity waters. Frequent marine storm-surge events transported marine waters and animals into floodplain lakes, where evaporation, interstitial sulphate-reducing bacteria, iron reduction and methanogenesis allowed dolomite growth in the shallow sub-surface. Secondary pedogenic modification (by roots, brecciation, desiccation, and soil forming processes) is common and represents lake evaporation with, in some cases, saline marsh development. The dolostone facies are part of a complex environmental mosaic of sub-aerial dry floodplain, wet marshy floodplains, rivers, and lakes ranging in salinity from freshwater to hypersaline. Marine influence is strongest at the base of the formation and decreases over time, as the floodplain became drier, and forested areas became more established. Coastal lakes were an important habitat for animals recovering from the end-Devonian Hangenberg Crisis and may have acted as a pathway for euryhaline fishes, molluscs and arthropods to access freshwater environments.

英国北部的Ballagan组提供了密西西比早期生态系统的杰出记录，该生态系统是随着四足动物出现在土地上而发展的。在本文中，我们研究了特威德河畔贝里克附近两个500米的地层剖面，这些剖面的特征是丰富的二茂铁白云岩层。确定了五个岩相：胶结粉砂岩和砂岩，均质白云岩，混合白云岩和粉砂岩，方解石和白云岩混合以及含蒸发矿物的白云岩。胶结沉积物具有非平面至平面的亚面白云石晶体，最大尺寸为40μm，而其他相则主要由大小为15μm的白云石或平面的正面体白云石菱形组成，较大的菱形斑块表明部分重结晶。蛇纹石，蛇足纲和球粒陨石化石；与罕见Spirorbis， chondrichthyans（Ageleodus，hybodonts和？ctenacanths，xenacanths），非gyracanth acanthodians，腹，广翅鲎，腕足动物，植物碎片，木，lycopsid根，木炭，大孢子，phycosiphoniform打洞，Zoophycos？和根瘤菌。白云石的氧和碳同位素组成范围从-3.6‰〜-1.7‰（对于δ ¹⁸ O）和-2.6‰〜+ 1.6‰（对于δ ¹³C）分别表示在混合盐度水中白云岩的生长。频繁的海洋风暴潮事件将海水和动物运到洪泛区的湖泊中，在这些湖泊中，蒸发，减少间质硫酸盐的细菌，铁的还原和甲烷化作用使白云岩在浅表层下生长。二次成岩作用的改良（通过根，角质化，干燥和土壤形成过程）很普遍，并且代表了湖泊的蒸发，在某些情况下还伴随着盐沼的发展。白云岩相是复杂的环境镶嵌的一部分，这些镶嵌环境包括盐度从淡水到高盐度的地下干洪泛区，湿沼泽洪泛区，河流和湖泊。海洋影响在地层的底部最强，并随着时间的流逝而减小，因为洪泛区变得更干燥，森林地区变得更加牢固。