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26-890: The other component formations of the Hastings Beds are the underlying Wadhurst Clay Formation and the Ashdown 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 Tunbridge Wells Sand Formation, were deposited during the Early Cretaceous Period, which lasted for approximately 40 million years from 140 to 100 million years ago. The Tunbridge Wells Sands are of Late Valanginian age. The Formation takes its name from

52-564: A major eustatic (global) transgression of the sea. The Greensand ( Aptian / Albian in age) consists of marine deposits. The sequence in the Weald Basin has also been described as a supergroup , containing the Weald Clay Group and Hastings Group. The Wealden Group forms outcrops covering a large part of south and south-eastern England including the Isle of Wight . It takes its name from

78-534: Is gradational elsewhere. In the area north of Brighton and west of Lewes the boundary is marked by a massive sandstone, though this is not seen anywhere else. Landslips often occur at or close to the lower boundary of the Tunbridge Wells Sands, between it and the underlying Wadhurst Clay Formation . This is partly caused by the steep sided hill, valley and ravine topography of the High Weald and partly by

104-522: Is lithologically similar to the older Wadhurst Clay and also has weathered red mottled clays at its top. The formation is up to 20m thick but is only present around the border of East Sussex and West Sussex . It can be further subdivided into the Lower Grinstead Clay and Upper Grinstead Clay. These divisions are separated by a lenticular calcareous sandstone known as the Cuckfield Stone. This

130-503: Is of Early to Late Valanginian age. 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. When they become exposed to

156-540: Is probably best known as the strata in which Gideon Mantell discovered Iguanodon in the early 19th century. The Upper Tunbridge Wells Sand is similar to the Lower Tunbridge Wells Sand. It comprises soft red and grey mottled silts and clays in its lower part, and alternating silts and silty clays with thin beds of sandstones. The base of the Tunbridge Wells Sand is marked by a distinct change from

182-476: 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

208-505: 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

234-607: The Hastings Beds . In Oxfordshire , Buckinghamshire and Wiltshire , the Wealden Group is only found as an outlier on top of hills and only consists of a single formation, the Whitchurch Sand Formation . In Yorkshire, the equivalently aged Speeton Clay Formation , a marine unit, is present. On top of the Wealden Group is the Lower Greensand Group . The difference between these two groups has been formed by

260-847: The Jurassic - Cretaceous boundary. Within the Wessex Basin , the Wealden Group consists of two formations : the Wessex Formation and overlying Vectis Formation . In the Weald Basin , the Wealden Group consists of four formations: the Ashdown Formation , the Wadhurst Clay Formation , the Tunbridge Wells Sand Formation and the Weald Clay Formation . The lower three formations are sometimes collectively referred to as

286-415: The Weald region of Kent , Sussex , Surrey and Hampshire . It has yielded many fossils, including dinosaurs like Iguanodon and Hypsilophodon . Apart from fossils, it shows many other signs of being deposited in a continental environment, such as mudcracks and -in some rare cases- dinosaur footprints. Taxa included in the table below have an uncertain provenance and cannot be placed into one of

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312-490: The Ardingly Sandstone forms a weathering-resistant layer, relative to the rest of the formation, which has become very popular with rock climbers and is known locally as Southern Sandstone . These are the closest rock climbing crags to London and as a result are the most heavily used in the country. The Grinstead Clay comprises mudstones and silty mudstones with siltstone, ironstone and shelly limestone. This member

338-582: 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 Wealden Group can be found in almost all Early Cretaceous basins of England: its outcrops curve from the Wessex Basin in the south to the Cleveland Basin in the northeast. It is not found in northwest England and Wales , areas which were at

364-669: The Mons Basin, including the Sainte-Barbe Clays Formation where large numbers of Iguanodon were found in the 19th century. Wadhurst Clay Formation 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

390-545: The Tunbridge Wells Sands from the overlying Grinstead Clay. This horizon is known as the Ardingly Sandstone and occurs in thicknesses of up to 18m. It is particularly well exposed throughout the region between East Grinstead , West Sussex , and Tunbridge Wells , Kent , at localities such as; Stone Farm south of East Grinstead ; Chiddinglye Rocks near West Hoathly ; Toad Rock, Bull's Hollow and Happy Valley west of Tunbridge Wells ; and Harrisons Rocks , Bowles Rocks and High Rocks near Tunbridge Wells . At all of these places

416-577: 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

442-469: The Wadhurst Clay, increasing the chances of failure. Hastings Beds The Wealden Group, occasionally also referred to as the Wealden Supergroup , is a group (a sequence of rock strata ) 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

468-678: The constituent formations, thus they are placed here. [REDACTED] The term "Wealden" and "Wealden facies" has been applied to other Lower Cretaceous sequences in Europe, including the "German Wealden", comprising the Berriasian aged Bückeberg Formation of the Lower Saxony Basin and in Belgium, where "Wealden facies" has been used as a term to refer to the Barremian-Aptian aged sequences of

494-504: The elements at the surface, the mudstones often degrade over a short period of time and weather to yellowish brown and greenish grey clays. 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 and in West Sussex up to 80m near Horsham . The base of

520-456: The lithological variation between the formations and the presence of spring lines and seepages. 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

546-403: The predominantly argillaceous sediments of the Wadhurst Clay to siltstones and silty sands. This boundary is often indicated on maps by spring lines and seepages, where groundwater percolating through the permeable Tunbridge Wells Sand is forced to surface at the junction with the Wadhurst Clay . The top of the Tunbridge Wells Sand Formation is well defined in the southwest of East Sussex but

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572-428: 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. 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. Natural slopes in the Wadhurst Clay, like those in

598-456: The spa town of Tunbridge Wells in Kent . The Tunbridge Wells Sand Formation comprises complex cyclic sequences of siltstones with sandstones and clays, typically fining upwards, and is lithologically similar to the older Ashdown Formation . It has a total thickness typically in the region of about 75 m. However, near Haywards Heath borehole data has proven the formation to be up to 150m thick. In

624-539: The time tectonic highs where no deposition took place. The same is true for the London Platform around London and Essex . Offshore, the Wealden Group can reach a thickness of 700 metres. The terms Wealden and Wealden facies are also used as generic terms referring to Early Cretaceous non-marine sequences elsewhere in Europe. The Wealden Group lies stratigraphically on top of the Purbeck Group , which spans

650-494: 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. When percolating groundwater in the permeable sandstones of the Tunbridge Wells Sands comes into contact with

676-764: The western parts of the High Weald the Tunbridge Wells Sands can be divided into four separate divisions; the Lower Tunbridge Wells Sand, the Ardingly Sandstone Member, the Grinstead Clay Member, and the Upper Tunbridge Wells Sand. The Lower Tunbridge Wells Sand shows the best cyclic fining up sequences in the formation. The division comprises mainly interbedded siltstones and silty sandstones and occurs up to 27m thick. A massive thick cross bedded fine to medium grained quartz sandstone separates

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