Wadhurst Clay Formation | |
---|---|
Stratigraphic range: | |
Type | Geological formation |
Unit of | Wealden Group |
Underlies | Tunbridge Wells Sand Formation |
Overlies | Ashdown Formation |
Thickness | 30 to 78 m |
Lithology | |
Primary | Shale, Mudstone |
Other | Siltstone, Sandstone, Limestone, Ironstone |
Location | |
Region | Europe |
Country | UK |
Extent | Weald Basin |
Type section | |
Named for | Wadhurst |
The Wadhurst Clay Formation is a geological unit which forms part of the Wealden Group and the middle part of the now unofficial Hastings Beds. These geological units make up the core of the geology of the High Weald in the English counties of West Sussex, East Sussex and Kent.
The other component formations of the Hastings Beds are the underlying Ashdown Formation and the overlying Tunbridge Wells Sand Formation. The Hastings Beds in turn form part of the Wealden Group which underlies much of southeast England. The sediments of the Weald, including the Wadhurst Clay Formation, were deposited during the Early Cretaceous Period, which lasted for approximately 40 million years from 140 to 100 million years ago. The Wadhurst Clay is of Early to Late Valanginian age. [1] The Formation takes its name from the market town of Wadhurst in East Sussex.
The Wadhurst Clay comprises predominantly medium to dark bluish grey over-consolidated clays, silts, mudstones, and shales. These lithologies often occur with subordinate amounts of pale grey silty mudstones, laminated siltstones, sandstones, conglomerate, shelly limestones and clay-ironstones. [2] When they become exposed to the elements at the surface, the mudstones often degrade over a short period of time and weather to yellowish brown and greenish grey clays. [3]
The formation thickness ranges from 55m in the Tenterden area, to 30m near Lewes and varies in between. In Kent, the Wadhurst Clay has been proven to over 70m thick near Tunbridge Wells [2] and in West Sussex up to 80m near Horsham. [4]
The base of the Wadhurst Clay is taken at the bottom of the Top Ashdown Pebble Bed. The base of this marker horizon marks the formational change to the Ashdown Formation. Despite its name this thin and impressistent bed comprises a coarse grained to gravelly sandstone. This horizon is best exposed at Cliff End, East Sussex, but where it is encountered elsewhere, it is usually fairly distinctive and easily identified. The Top Ashdown Pebble Bed occurs mainly in the southern half of East Sussex and is often missing elsewhere. Where this is the case, the boundary is taken at a layer of disconnected ripples. [5]
The top of the Wadhurst Clay is marked by a distinct lithological change into the siltstones of the Tunbridge Wells Sand Formation. The uppermost clays of the Wadhurst Clay, closest to the boundary are often stained red. [1]
Natural slopes in the Wadhurst Clay, like those in the Ashdown Formation, are known for their instability, especially where impermeable clays and impermeable silts and siltstones are interbedded. Instability, resulting in landslips, often occurs along shear surfaces and weaknesses that originally developed during the Late Devensian glaciation. Other common features include cambering, valley bulging and solifluction lobes.
Landslips often occur at or close to the upper boundary of the Wadhurst Clay, which is shared with the overlying Tunbridge Wells Sand Formation. This is partly caused by the steep sided hill, valley and ravine topography of the High Weald and partly by the lithological variation between the formations and the presence of spring lines and seepages. [3]
When percolating groundwater in the permeable sandstones of the Tunbridge Wells Sands comes into contact with the upper impermeable clay beds of the Wadhurst Clay, it is forced to find alternative migration pathways to the surface. This results in the saturation and weakening of the upper portion of the Wadhurst Clay, increasing the chances of failure. [3]
Taken from [6]
Fish reported from the Wadhurst Clay | ||||||
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Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
Egertonodus | E. basanus | Ashdown Brickworks [7] | Hybodont shark | |||
Planohybodus | P. ensis | |||||
Polyacrodus | P. parvidens, P. brevicostatus | |||||
Ocloedus | Pycnodontiform | |||||
Coccolepis | Coccolepidid [8] | |||||
Semionotiformes, | ||||||
Albuliformes |
Dinosaurs reported from the Wadhurst Clay | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
Altispinax | A. dunkeri | Hollington Quarry | Tooth | An carnosaurian theropod | ||
Barilium | B. dawsoni [9] | Shornden Quarry, Old Roar Quarry, | "[Two] partial skeletons." [10] | An iguanodontian | ||
Unnamed dromaeosaurid | Indeterminate | |||||
Hypselospinus | H. fittoni [9] | Hollington Quarry, Shornden Quarry, Hare Farm Lane, Brede | Partial skeletons | An iguanodontian | ||
Suchosaurus | S. cultridens | Hare Farm Lane, Brede | Teeth | A spinosaurid theropod | ||
Unnamed maniraptoran | Indeterminate | Ashdown Brickworks | Specimen BEXHM: 2008.14.1 [11] A single cervical vertebra | Possibly an oviraptorosaur [11] | ||
Unnamed spinosaurid | Indeterminate | |||||
Unammed tyrannosauroid | Indeterminate | |||||
Amphibians reported from the Wadhurst Clay | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
Anura | Indeterminate | Ashdown Brickworks | Two fragmentary ilia | At least 2 taxa [12] | ||
Urodela | Indeterminate | Atlas and postatlas vertebrae, dentary, maxilla and vomer fragments | At least 3 taxa distinguishable by their atlas vertebrae [12] |
Crocodyliformes reported from the Wadhurst Clay | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
Goniopholis | G. crassidens | Hare Farm Lane, Brede | A Goniopholid neosuchian | |||
Hulkepholis | Indeterminate | Ashdown Brickworks [7] | A goniopholid neosuchian | |||
Theriosuchus | An atoposaurid neosuchian | |||||
Bernissartiidae |
Mammals reported from the Wadhurst Clay | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
Laolestes | L. hodsoni | Cliff End bonebed, Tighe Farm | Cypridea paulsgrovensis ostracod Zone | A dryolestid mammal | ||
Spalacotherium | S. tricuspidens | Cliff End bonebed | A spalacotheriid mammal | |||
Aegialodon | A. dawsoni | A cladotherian mammal | ||||
Loxaulax | L. valdensis | A eobataarid multituberculate |
Plesiosaurians reported from the Wadhurst Clay | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
Hastanectes | H. valdensis | Old Roar Quarry, Hollington Quarry, Black Horse Quarry, Hastings, Brenchley | A leptocleidid plesiosaur |
Pterosaurs reported from the Wadhurst Clay Formation | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
? Istiodactylidae indet. | Indeterminate | Cliff End Bone Bed, Cliff End. [13] | 2 isolated tooth crowns (BEXHM: 2022.109.1 & BEXHM: 2022.109.2). [13] | An istiodactylid. | ||
Ashdown Forest is an ancient area of open heathland occupying the highest sandy ridge-top of the High Weald Area of Outstanding Natural Beauty. It is situated 30 miles (48 km) south of London in the county East Sussex, England. Rising to an elevation of 732 feet (223 m) above sea level, its heights provide expansive vistas across the heavily wooded hills of the Weald to the chalk escarpments of the North Downs and South Downs on the horizon.
The Weald is an area of South East England between the parallel chalk escarpments of the North and the South Downs. It crosses the counties of Hampshire, Surrey, West Sussex, East Sussex, and Kent. It has three parts, the sandstone "High Weald" in the centre, the clay "Low Weald" periphery and the Greensand Ridge, which stretches around the north and west of the Weald and includes its highest points. The Weald once was covered with forest and its name, Old English in origin, signifies "woodland". The term is still used, as scattered farms and villages sometimes refer to the Weald in their names.
Weald Clay or the Weald Clay Formation is a Lower Cretaceous sedimentary rock unit underlying areas of South East England, between the North and South Downs, in an area called the Weald Basin. It is the uppermost unit of the Wealden Group of rocks within the Weald Basin, and the upper portion of the unit is equivalent in age to the exposed portion of the Wessex Formation on the Isle of Wight. It predominantly consists of thinly bedded mudstone. The un-weathered form is blue/grey, and the yellow/orange is the weathered form, it is used in brickmaking.
The Purbeck Group is an Upper Jurassic to Lower Cretaceous lithostratigraphic group in south-east England. The name is derived from the district known as the Isle of Purbeck in Dorset where the strata are exposed in the cliffs west of Swanage.
Valdoraptor is a genus of theropod dinosaur from the Early Cretaceous. Its fossils were found in England. It is known only from bones of the feet. The holotype, BMNH R2559, was found near Cuckfield in layers of the Tunbridge Wells Sand Formation dating from the late Valanginian. The specimen is damaged lacking parts of the upper and lower ends. It has a conserved length of 215 millimetres (8.5 in) and an estimated length of 240 millimetres (9.4 in). This genus is paleontologically significant for being the first ornithomimosaur specimen known from England and represents the earliest record of ornithomimosaurs.
The Wealden Group, occasionally also referred to as the Wealden Supergroup, is a group in the lithostratigraphy of southern England. The Wealden group consists of paralic to continental (freshwater) facies sedimentary rocks of Berriasian to Aptian age and thus forms part of the English Lower Cretaceous. It is composed of alternating sands and clays. The sandy units were deposited in a flood plain of braided rivers, the clays mostly in a lagoonal coastal plain.
The Vale of Kent, located in Kent, England, is the name given to the broad clay vale between the Greensand Ridge and the High Weald. The area is drained by a number of rivers, including the Beult, Eden, Medway, Stour and River Teise.
The Greensand Ridge, also known as the Wealden Greensand, is an extensive, prominent, often wooded, mixed greensand/sandstone escarpment in south-east England. Forming part of the Weald, a former dense forest in Sussex, Surrey and Kent, it runs to and from the East Sussex coast, wrapping around the High Weald and Low Weald. It reaches its highest elevation, 294 metres (965 ft), at Leith Hill in Surrey—the second highest point in south-east England, while another hill in its range, Blackdown, is the highest point in Sussex at 280 metres (919 ft). The eastern end of the ridge forms the northern boundary of Romney Marsh.
Kent is the south-easternmost county in England. It is bounded on the north by the River Thames and the North Sea, and on the south by the Straits of Dover and the English Channel. The continent of Europe is 21 miles across the straits.
Sussex is a historic county and cultural region in the south of England corresponding roughly in area to the ancient Kingdom of Sussex. It is bounded on the north by Surrey, north-east by Kent, south by the English Channel, and west by Hampshire, and is divided for local government into West Sussex and East Sussex and the city of Brighton and Hove. The city of Brighton & Hove was created a unitary authority in 1997, and was granted City status in 2000. Until then Chichester had been Sussex's only city. By convention, Chichester is Sussex's capital city and Lewes is Sussex's county town.
The Wessex Formation is a fossil-rich English geological formation that dates from the Berriasian to Barremian stages of the Early Cretaceous. It forms part of the Wealden Group and underlies the younger Vectis Formation and overlies the Durlston Formation. The dominant lithology of this unit is mudstone with some interbedded sandstones. It is part of the strata of the Wessex Basin, exposed in both the Isle of Purbeck and the Isle of Wight. While the Purbeck sections are largely barren of vertebrate remains, the Isle of Wight sections are well known for producing the richest and most diverse fauna in Early Cretaceous Europe.
St Leonard's Forest is at the western end of the Wealden Forest Ridge which runs from Horsham to Tonbridge, and is part of the High Weald Area of Outstanding Natural Beauty. It lies on the ridge to the south of the A264 between Horsham and Crawley with the villages of Colgate and Lower Beeding within it. The A24 lies to west and A23 to the East and A272 through Cowfold to the south. Much has been cleared, but a large area is still wooded. Forestry England has 289 ha. which is open to the public, as are Owlbeech and Leechpool Woods to the east of Horsham, and Buchan Country Park to the SW of Crawley. The rest is private with just a few public footpaths and bridleways. Leonardslee Gardens were open to the public until July 2010 and re-opened in April 2019. An area of 85.4 hectares is St Leonards Forest Site of Special Scientific Interest.
The Lower Greensand Group is a geological unit present across large areas of Southern England. It was deposited during the Aptian and Albian ages of the Early Cretaceous. It predominantly consists of sandstone and unconsolidated sand that were deposited in shallow marine conditions.
The geology of East Sussex is defined by the Weald–Artois anticline, a 60 kilometres (37 mi) wide and 100 kilometres (62 mi) long fold within which caused the arching up of the chalk into a broad dome within the middle Miocene, which has subsequently been eroded to reveal a lower Cretaceous to Upper Jurassic stratigraphy. East Sussex is best known geologically for the identification of the first dinosaur by Gideon Mantell, near Cuckfield, to the famous hoax of the Piltdown Man near Uckfield.
The Tunbridge Wells Sand Formation is a geological unit which forms part of the Wealden Group and the uppermost and youngest part of the unofficial Hastings Beds. These geological units make up the core of the geology of the Weald in the English counties of West Sussex, East Sussex and Kent.
The Ashdown Formation is a geological unit, which forms part of the Wealden Group and the lowermost and oldest part of the now unofficial Hastings Beds. These geological units make up the core of the Weald in the English counties of East Sussex and Kent.
The geology of Kent in southeast England largely consists of a succession of northward dipping late Mesozoic and Cenozoic sedimentary rocks overlain by a suite of unconsolidated deposits of more recent origin.
The geology of West Sussex in southeast England comprises a succession of sedimentary rocks of Cretaceous age overlain in the south by sediments of Palaeogene age. The sequence of strata from both periods consists of a variety of sandstones, mudstones, siltstones and limestones. These sediments were deposited within the Hampshire and Weald basins. Erosion subsequent to large scale but gentle folding associated with the Alpine Orogeny has resulted in the present outcrop pattern across the county, dominated by the north facing chalk scarp of the South Downs. The bedrock is overlain by a suite of Quaternary deposits of varied origin. Parts of both the bedrock and these superficial deposits have been worked for a variety of minerals for use in construction, industry and agriculture.
The Whitchurch Sand Formation is a geological formation, in England. part of the Wealden Group, it is preserved as an inlier in hills in Buckinghamshire, Oxfordshire and Wiltshire. It was deposited in the Valanginian stage of the Early Cretaceous. The lithology largely consists of unconsolidated fine-medium grained sand with isolated bodies of limonite cemented sandstone, with localised beds of siltstone and mudstone.
The geology of the South Downs National Park in South East England comprises a gently folded succession of sedimentary rocks from the Cretaceous and early Palaeogene periods overlain in places by a range of superficial deposits from the last 2.6 million years. Whereas the South Downs are formed from the Late Cretaceous age chalk, the South Downs National Park extends into the Weald to the north of the range and thereby includes older rock strata dating from the Early Cretaceous including sandstones and mudstones. The youngest solid rocks are found on the southern fringes of the National Park in the eastern extension of the Hampshire Basin and include sand, silt and clay deposited during the Palaeocene and Eocene epochs.
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