Tunbridge Wells Sand Formation

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Tunbridge Wells Sand Formation
Stratigraphic range: Late Valanginian
Cliffs by beach at Bexhill-on-Sea in England - 2008-07-13 L.jpg
Cliffs of Tunbridge Wells Sand at Bexhill-on-Sea
Type Geological formation
Unit of Wealden Group
Sub-units
  • Upper Tunbridge Wells Sand Member
  • Grinstead Clay Member
  • Ardingly Sandstone Member
  • Lower Tunbridge Wells Sand Member
Underlies Weald Clay
Overlies Wadhurst Clay Formation
ThicknessGenerally 75 m, but varies from 46 to 122 m
Lithology
Primary Sandstone, Siltstone
Other Mudstone, Limestone
Location
Region Europe
CountryFlag of the United Kingdom.svg  UK
Extent Weald Basin
Type section
Named for Royal Tunbridge Wells

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.

Contents

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. [1] The Formation takes its name from the spa town of Tunbridge Wells in Kent.

Lithology

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. [2] It has a total thickness typically in the region of about 75 m. [1] However, near Haywards Heath borehole data has proven the formation to be up to 150m thick. [3]

In 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. [3]

Lower Tunbridge Wells Sand

A climber scales the Ardingly Sandstone at Bowles Rocks near Crowborough Bowles Rocks.jpg
A climber scales the Ardingly Sandstone at Bowles Rocks near Crowborough

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. [4]

Ardingly Sandstone Member

A massive thick cross bedded fine to medium grained quartz sandstone separates 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 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. [5]

Grinstead Clay Member

The Grinstead Clay comprises mudstones and silty mudstones with siltstone, ironstone and shelly limestone. This member 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. [3] These divisions are separated by a lenticular calcareous sandstone known as the Cuckfield Stone. This is probably best known as the strata in which Gideon Mantell discovered Iguanodon in the early 19th century.

Upper Tunbridge Wells Sand

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 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 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. [4]

Engineering Geology

Translational landslip at the boundary of the Wadhurst Clay and Tunbridge Wells Sand near Etchingham Landslip.jpg
Translational landslip at the boundary of the Wadhurst Clay and Tunbridge Wells Sand near Etchingham

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 the lithological variation between the formations and the presence of spring lines and seepages. [2]

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. [2]

Paleobiota

Pterosaurs

Pterosaurs reported from the Tunbridge Wells Sands
GenusSpeciesLocationStratigraphic positionMaterialNotesImages
Serradraco S. sagittirostrisSt.-Leonards-on-SeaUpper Tunbridge Wells SandsLower Jaw, vertebraeAn ornithocheiromorph
Serradraco sagittirostris Kellner and Rodriguez 2013.jpg

Crocodyliformes

Crocodyliformes reported from the Tunbridge Wells Sands
GenusSpeciesLocationStratigraphic positionMaterialNotesImages
Hulkepholis H. willettiCuckfieldGrinstead Clay
Goniopholis IndeterminatePevensey Pit, Ashdown BrickworksLower Tunbridge Wells Sand

Turtles

Turtles reported from the Tunbridge Wells Sands
GenusSpeciesLocationStratigraphic positionMaterialNotesImages
Helochelydra“Helochelydra” bakewelliCuckfieldGrinstead ClayShell fragmentsA helochelydrid turtle, unclear whether it actually belongs to Helochelydra [6]

Dinosaurs

Dinosaurs reported from the Tunbridge Wells Sands
GenusSpeciesLocationStratigraphic positionMaterialNotesImages
Barilium B. dawsoni [7] Whiteman’s Green, CuckfieldGrinstead ClayLower JawAn iguanodontian, originally given the name Kukufeldia
Kukufeldia holotype.jpg
Regnosaurus [8] R. northamptoni [8] Tilgate Forest, CuckfieldGrinstead Clay MemberLower jawNomen dubium. [8]
Regnosaurus.jpg
Hylaeosaurus [9] H. armatus [9] "Partial skull, skeleton, isolated postcrania." [10]
Hylaeosaurus armatus.png
Suchosaurus S. cultridensTeethA spinosaurid
Suchosaurus.jpg
Valdoraptor [8] V. oweni [8] Cuckfield"Metatarsals." [11] An ornithomimosaur
Valdoraptor.jpg
Pelorosaurus [9] P. conybeari [8] Cuckfield Quarry, Tilgate" Humerus (Holotype) [and four] caudal vertebrae." [12] These were found separately and might belong to different taxaA basal titanosauriform Pelorosaurus.PNG

Mammals

Mammals reported from the Tumbridge Wells Sands
GenusSpeciesLocationStratigraphic positionMaterialNotesImages
?Aegialodon ?A. dawsoniPaddockhurst bone bedGrinstead Clay
Spalacotherium S. taylori
Loxaulax L. valdensis

See also

Related Research Articles

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<span class="mw-page-title-main">Weald</span> Area of South East England

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 separate 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 today, as scattered farms and villages sometimes refer to the Weald in their names.

<span class="mw-page-title-main">Weald Clay</span> Geological formation in England

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<span class="mw-page-title-main">Wealden Group</span> Stratigraphic Group in England

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<span class="mw-page-title-main">Greensand Ridge</span> Range of hills in south east England, UK

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.

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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.

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<span class="mw-page-title-main">Wadhurst Clay Formation</span>

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References

  1. 1 2 Hopson, P.M., Wilkinson, I.P. and Woods, M.A. (2010) A stratigraphical framework for the Lower Cretaceous of England. Research Report RR/08/03. British Geological Survey, Keyworth.
  2. 1 2 3 Codd, J.W. (2007) Analysis of the distribution and characteristics of landslips in the Weald of East Sussex. MSc dissertation, University of Brighton.
  3. 1 2 3 Young, B. & Lake, R.D. (1988) Geology of the country around Brighton and Worthing: Memoir for 1:50,000 geological sheets 318 and 333. British Geological Survey, London.
  4. 1 2 Lake, R.D. & Shepard-Thorn, E.R. (1987) Geology of the country around Hastings and Dungeness: Memoir for 1:50,000 geological sheets 320 and 321. British Geological Survey, London.
  5. Messenger, Alex (9 July 2011). "Southern Sandstone: guidelines". The British Mountaineering Council.
  6. Joyce, Walter G. (April 2017). "A review of the fossil record of basal Mesozoic turtles" (PDF). Bulletin of the Peabody Museum of Natural History. 58 (1): 65–113. doi:10.3374/014.058.0105. S2CID   54982901 . Retrieved July 9, 2017.
  7. "10.19 East Sussex, England; 1. Hastings Beds" in Weishampel, et al. (2004). Page 559.
  8. 1 2 3 4 5 6 "10.18 West Sussex, England; 1. Hastings Beds" in Weishampel, et al. (2004). Page 559.
  9. 1 2 3 "10.19 East Sussex, England; 1. Hastings Beds" and "10.18 West Sussex, England; 1. Hastings Beds" in Weishampel, et al. (2004). Page 559.
  10. "Table 17.1," in Weishampel, et al. (2004). Page 366.
  11. "Table 4.1," in Weishampel, et al. (2004). Page 77.
  12. "Table 13.1," in Weishampel, et al. (2004). Page 266.