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| Sussex Group | |
|---|---|
| Name | Sussex Group |
| Type | Geological group |
| Age | Carboniferous (Carboniferous) |
| Period | Carboniferous |
| Region | Sussex, England; adjacent areas |
| Country | United Kingdom |
| Subunits | Ashdown Formation; Wadhurst Clay Formation; Tunbridge Wells Sand Formation; Weald Clay Formation |
Sussex Group
The Sussex Group is a lithostratigraphic succession of sedimentary rock units exposed across parts of East Sussex, West Sussex, and neighboring counties in southern England. It forms a major component of the southern Wealden outcrop and records continental to marginal marine deposition during the Early Cretaceous and late Jurassic intervals as interpreted in regional syntheses. The Group has been integral to understanding basin development in the Weald Basin and has been the subject of studies by institutions such as the British Geological Survey and universities including the University of Oxford and the University of Cambridge.
The Sussex Group comprises a stacked sequence of formations including the Ashdown Formation, the Wadhurst Clay Formation, the Tunbridge Wells Sand Formation, and the Weald Clay Formation in varying local successions. Lithologies range from fluvial sandstones and conglomerates in the Ashdown Formation to marine-influenced clays and mudstones in the Wadhurst Clay Formation, with laterally extensive silty sandstones in the Tunbridge Wells Sand Formation and thick mudstones in the Weald Clay Formation. Primary facies include channelized coarse-grained sandstones, heterolithic floodplain deposits, carbonaceous mudstones, sideritic concretion horizons, and localized ironstone bands that have been correlated with marker beds recognized on the South Downs escarpment and coastal exposures at Hastings and Beachy Head.
Biostratigraphic and radiometric frameworks place much of the Sussex Group within the latest Jurassic to Early Cretaceous time span, commonly correlated with the Tithonian to Valanginian stages in international stages. Palynological assemblages and vertebrate biostratigraphy have been used to correlate beds with contemporaneous units in the Hauterivian–Barremian intervals where regional unconformities permit. Correlations have been drawn between the Sussex succession and equivalent sequences in the Weald Basin, the Broads Basin, and offshore facies encountered in North Sea exploration wells drilled by companies such as BP and Shell.
Depositional environments represented in the Sussex Group include low-sinuosity river systems, crevasse-splay and floodplain settings, coastal lagoons, and ephemeral lakes within a subsiding intracontinental basin. Sedimentology and paleocurrent data indicate provenance from uplifted source areas to the north and east, including parts of the London Platform and adjacent basement highs. Tectonic controls related to the opening of the Atlantic Ocean and the evolution of the Weald-Artois Anticline influenced accommodation and drainage patterns, producing lateral facies changes from fluvial channel sandstones to estuarine and marginal marine clays. Paleogeographic reconstructions link Sussex Group environments with contemporaneous coastal plains documented in southern England and northern France.
The Sussex Group is fossiliferous, yielding terrestrial and marginal marine assemblages including dinosaur remains, crocodylomorphs, turtles, charophytes, ostracods, bivalves, and diverse plant megafossils. Notable vertebrate finds have been made near Hastings and Tunbridge Wells, providing data used in studies by paleontologists associated with the Natural History Museum, London and the British Museum (Natural History). Palynological records—spores and pollen—have been crucial for biostratigraphy and paleoenvironmental interpretation, while invertebrate assemblages assist correlation with continental shelf deposits described from the Channel Basin and Paris Basin research. Ichnofauna, including dinosaur trackways recorded in coastal exposures, have been documented by teams from institutions such as the Geological Society of London.
Historically, sandstones of the Sussex Group provided building stone and dimension stone exploited in towns such as Lewes and Hastings; ironstone bands were mined during the 18th and 19th centuries to supply local ironworks including firms linked to the Sussex iron industry. Clay-rich horizons have been used for brickmaking and tile production supporting manufacturers in the Weald during the Industrial Revolution and later. The Group’s aquifer properties in coarse-grained sand units are utilized for groundwater supply in municipal systems managed by utilities including Southern Water. Petroleum exploration in adjacent basins has targeted deeper equivalents, and aggregate extraction continues under the oversight of county planning authorities such as East Sussex County Council.
Early observations of the Sussex succession date to the 18th and 19th centuries by naturalists and geologists such as William Smith, Gideon Mantell, and members of the Geological Society of London, who documented fossils and mapped coastal sections near Hastings and Beachy Head. Systematic mapping and formal lithostratigraphic definition were advanced in the 20th century by the British Geological Survey and academic workers at the University of Sussex and the University of Oxford. Recent multidisciplinary studies integrating sedimentology, palynology, and sequence stratigraphy have refined age models and basin reconstructions, with contributions from research groups at the Natural History Museum, London and European collaborators in France and the Netherlands.
Exposures of the Group occur across the Wealden anticline, along the Hastings Beds coastline, and in inland quarries and boreholes from Hastings westwards toward Brighton and north into Kent. Subunits recognized at varying stratigraphic levels include the Ashdown Formation, Wadhurst Clay Formation, Tunbridge Wells Sand Formation, and Weald Clay Formation, each subdivided into members and beds in detailed maps by the British Geological Survey. Correlative successions continue offshore and beneath younger cover sedimentary packages encountered in basinal studies by organizations such as BGS and industry partners.
Category:Geologic groups of the United Kingdom Category:Geology of Sussex