Volcanic Margins Research Consortium
The rise of a new terrestrial ecosystem in the Early Carboniferous.
Examples of early Mississippian terrestrial habitats from palaeoequatorial regions are preserved in sedimentary rocks that crop out across the borders of England and Scotland as the Tournaisian Ballagan Formation. New discoveries of land-based tetrapod taxa in this formation are of international importance because tetrapods were thought to be very uncommon in this part of the geological record. Early Mississippian finds provide a new insight into the late Devonian primitive aquatic forms and the terrestrial fauna with robust pentadactyl limbs recovered from late Mississippian successions. The Ballagan Formation represents deposition across an extensive coastal-alluvial plain. Fluvial systems include multi-storey meandering and sheet-like bodies and single channel forms. Diverse palaeosols, with a dominance of entisols and inceptisols, suggest relatively brief periods of soil development on the floodplain. Mean annual rainfall estimates from palaeosol compositions are 1000–1500 mm yr-1. Detailed palynological analysis provide insights to the changing vegetation. Key vertebrate (actinopterygians, rhizodonts, dipnoans, chondrichthyans and tetrapods), invertebrate and plant fossils are preserved in sandy siltstones, a previously under-recognised floodplain facies. Interpreted as the deposits of cohesive debris flows, originating from overbank floods and localised floodplain transport at times of high rainfall, these matrix-supported siltstones incorporate lithic clasts and preserve some fossils with a greater degree of articulation compared to those found in basal conglomerates of fluvial channel sandstones. Dolostone beds from successions in the Scottish Borders represent an unusual floodplain lake environment, inhabited by actinoptergyians, rhizodonts, molluscs and ostracods. An associated ichnofauna indicates repeated, short-lived marine interactions. These marine incursions influenced lake development and evaporite-bearing beds are associated with dolostones. Dolostones in Northumberland, further south, represent more lagoonal to marginal marine settings. Extensive evaporites in these Lower Mississippian successions have commonly been used as evidence for an arid to semi-arid palaeoclimate however, their context (including data from palaeosol types and geochemical proxies, and from palaeobotanical evidence) indicates a strongly seasonal palaeoclimate at this time. The early Mississippian tetrapods occupied a complex and dynamic mosaic of sub-environments that existed for many million years and the region provided a range of habitats for tetrapods to develop terrestrial capabilities and suitable settings for their preservation.
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The Volcanic Margins Research Consortium (VMRC) provides the petroleum industry with training and research expertise in volcanology, sedimentology and structural geology of volcanic margins. The consortium comprises academic staff at the universities of Durham, Aberdeen, Glasgow, Leicester and CASP, and industry partners involved in the development of hydrocarbon prospects in the North Atlantic Igneous Province and the Faroes-Shetland Basin.
Training takes place during workshops, in the laboratory and on field courses and each industrial partner has the opportunity to fund PhD projects through the member universities.
VMRC Leader: Richard Brown