Palaeoecology and palaeoenvironment of Mississippian coastal lakes and marshes during the early terrestrialisation of tetrapods

Bennett, C. E.; Kearsey, T. I.; Davies, S. J.; Leng, M. J.; Millward, D.; Smithson, T. R.; Brand, P. J.; Browne, M. A.E.; Carpenter, D. K.; Marshall, J. E.A.; Dulson, H.; Curry, L.

Abstract

© 2020 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.

Citation

Bennett, C. E., Kearsey, T. I., Davies, S. J., Leng, M. J., Millward, D., Smithson, T. R., Brand, P. J., Browne, M. A., Carpenter, D. K., Marshall, J. E., Dulson, H., & Curry, L. (2021). Palaeoecology and palaeoenvironment of Mississippian coastal lakes and marshes during the early terrestrialisation of tetrapods. Palaeogeography, Palaeoclimatology, Palaeoecology, 564, Article 110194. https://doi.org/10.1016/j.palaeo.2020.110194

• Journal Article Type: Article
• Acceptance Date: Dec 20, 2020
• Online Publication Date: Dec 27, 2020
• Publication Date: Feb 15, 2021
• Deposit Date: Jan 6, 2021
• Publicly Available Date: Dec 28, 2021
• Journal: Palaeogeography, Palaeoclimatology, Palaeoecology
• Print ISSN: 0031-0182
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 564
• Article Number: 110194
• DOI: https://doi.org/10.1016/j.palaeo.2020.110194
• Keywords: Earth-Surface Processes; Palaeontology; Ecology, Evolution, Behavior and Systematics; Oceanography
• Public URL: https://nottingham-repository.worktribe.com/output/5202851
• Publisher URL: https://www.sciencedirect.com/science/article/pii/S0031018220306428