The Tunbridge Wells Sand Formation is a geological unit which forms part of the

Wealden Group The Wealden Group, occasionally also referred to as the Wealden Supergroup, is a group (stratigraphy), group (a sequence of rock strata) in the lithostratigraphy of southern England. The Wealden group consists of wiktionary:paralic, paralic to c ...

and the uppermost and youngest part of the unofficial Hastings Beds. These geological units make up the core of the

geology Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth ...

of the

Weald 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 W ...

in the English counties of

West Sussex West Sussex is a Ceremonial counties of England, ceremonial county in South East England. It is bordered by Surrey to the north, East Sussex to the east, the English Channel to the south, and Hampshire to the west. The largest settlement is Cr ...

East Sussex East Sussex is a Ceremonial counties of England, ceremonial county in South East England. It is bordered by Kent to the north-east, West Sussex to the west, Surrey to the north-west, and the English Channel to the south. The largest settlement ...

and

Kent Kent is a Ceremonial counties of England, ceremonial county in South East England. It is bordered by Essex across the Thames Estuary to the north, the Strait of Dover to the south-east, East Sussex to the south-west, Surrey to the west, and Gr ...

. 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

which underlies much of southeast

England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...

. The sediments of the

, including the Tunbridge Wells Sand Formation, were deposited during the

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

Period, which lasted for approximately 40 million years from 140 to 100 million years ago. The Tunbridge Wells Sands are of Late

Valanginian In the geologic timescale, the Valanginian is an age or stage of the Early or Lower Cretaceous. It spans between 137.05 ± 0.2 Ma and 132.6 ± 0.2 Ma (million years ago). The Valanginian Stage succeeds the Berriasian Stage of the Lower Cretac ...

age.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. The Formation takes its name from the spa town of

Tunbridge Wells Royal Tunbridge Wells (formerly, until 1909, and still commonly Tunbridge Wells) is a town in Kent, England, southeast of Central London. It lies close to the border with East Sussex on the northern edge of the High Weald, whose sandstone ...

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.Codd, J.W. (2007) ''Analysis of the distribution and characteristics of landslips in the Weald of East Sussex''. MSc dissertation, University of Brighton. It has a total thickness typically in the region of about 75 m. However, near

Haywards Heath Haywards Heath ( ) is a town in West Sussex, England, south of London, north of Brighton, south of Gatwick Airport and northeast of the county town, Chichester. Nearby towns include Burgess Hill to the southwest, Horsham to the northwest, ...

borehole data has proven the formation to be up to 150m thick.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. In the western parts of the High

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.

Lower 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.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.

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 East Grinstead () is a town in West Sussex, England, near the East Sussex, Surrey, and Kent borders, south of London, northeast of Brighton, and northeast of the county town of Chichester. Situated in the northeast corner of the county, bord ...

, and

, at localities such as; Stone Farm south of

; Chiddinglye Rocks near West Hoathly; Toad Rock, Bull's Hollow and Happy Valley west of

; and Harrisons Rocks, Bowles Rocks and High Rocks near

. 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 Rock climbing is a climbing sports discipline that involves ascending climbing routes, routes consisting of natural rock in an outdoor environment, or on artificial resin climbing walls in a mostly indoor environment. Routes are documented in c ...

crags to

London London is the Capital city, capital and List of urban areas in the United Kingdom, largest city of both England and the United Kingdom, with a population of in . London metropolitan area, Its wider metropolitan area is the largest in Wester ...

and as a result are the most heavily used in the country.

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

and

. 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 is probably best known as the strata in which

Gideon Mantell Gideon Algernon Mantell Membership of the Royal College of Surgeons, MRCS Fellow of the Royal Society, FRS (3 February 1790 – 10 November 1852) was an English obstetrician, geologist and paleontology, palaeontologist. His attempts to reconstr ...

discovered

Iguanodon ''Iguanodon'' ( ; meaning 'iguana-tooth'), named in 1825, is a genus of iguanodontian dinosaur. While many species found worldwide have been classified in the genus ''Iguanodon'', dating from the Late Jurassic to Early Cretaceous, Taxonomy (bi ...

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

but is gradational elsewhere. In the area north of

Brighton Brighton ( ) is a seaside resort in the city status in the United Kingdom, city of Brighton and Hove, East Sussex, England, south of London. Archaeological evidence of settlement in the area dates back to the Bronze Age Britain, Bronze Age, R ...

and west of

Lewes Lewes () is the county town of East Sussex, England. The town is the administrative centre of the wider Lewes (district), district of the same name. It lies on the River Ouse, Sussex, River Ouse at the point where the river cuts through the Sou ...

the boundary is marked by a massive sandstone, though this is not seen anywhere else.

Engineering Geology

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. 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.

Paleobiota

Pterosaurs

Crocodyliformes

Turtles

Dinosaurs

Mammals

References

{{Reflist

External links

British Geological Survey lexicon
Geologic formations of England Lower Cretaceous Series of Europe Cretaceous England Valanginian Stage Sandstone formations