The Wealden Group, occasionally also referred to as the Wealden Supergroup, is a group (a sequence of

rock strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as e ...

) in the lithostratigraphy of southern

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe ...

. The Wealden group consists of paralic to

continent A continent is any of several large landmasses. Generally identified by convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continents. Ordered from largest in area to smallest, these seven ...

al (freshwater)

facies In geology, a facies ( , ; same pronunciation and spelling in the plural) is a body of rock with specified characteristics, which can be any observable attribute of rocks (such as their overall appearance, composition, or condition of formatio ...

sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

s of

Berriasian In the geological timescale, the Berriasian is an age/stage of the Early/Lower Cretaceous. It is the oldest subdivision in the entire Cretaceous. It has been taken to span the time between 145.0 ± 4.0 Ma and 139.8 ± 3.0 Ma (million years ag ...

Aptian The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous Epoch or Series and encompasses the time from 121.4 ± 1.0 Ma to 113.0 ± 1.0 Ma (million years ag ...

age and thus forms part of the English

Lower Cretaceous Lower may refer to: * Lower (surname) * Lower Township, New Jersey *Lower Receiver (firearms) * Lower Wick Gloucestershire, England See also *Nizhny Nizhny (russian: Ни́жний; masculine), Nizhnyaya (; feminine), or Nizhneye (russian: Н� ...

. It is composed of alternating

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class ...

s and

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay pa ...

s. The sandy units were deposited in a

flood plain A floodplain or flood plain or bottomlands is an area of land adjacent to a river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.Goudi ...

braided river A braided river, or braided channel, consists of a network of river channels separated by small, often temporary, islands called braid bars or, in English usage, ''aits'' or ''eyots''. Braided streams tend to occur in rivers with high sediment ...

s, the clays mostly in a

lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into '' coastal lagoons'' (or ''barrier lagoons ...

al coastal plain.Jackson (2008) 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 Wales ( cy, Cymru ) is a country that is part of the United Kingdom. It is bordered by England to the east, the Irish Sea to the north and west, the Celtic Sea to the south west and the Bristol Channel to the south. It had a population in ...

, areas which were at the time tectonic highs where no deposition took place. The same is true for the London Platform around London and

Essex Essex () is a Ceremonial counties of England, county in the East of England. One of the home counties, it borders Suffolk and Cambridgeshire to the north, the North Sea to the east, Hertfordshire to the west, Kent across the estuary of the Riv ...

. Offshore, the Wealden Group can reach a thickness of 700 metres. The terms ''Wealden'' and ''Wealden

'' are also used as generic terms referring to Early Cretaceous non-marine sequences elsewhere in Europe.

Stratigraphy

The Wealden Group lies stratigraphically on top of the Purbeck Group, which spans the

Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

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 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 a ...

, the

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 ...

, the

Tunbridge Wells Sand Formation 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 c ...

and the

Weald Clay Formation 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 ...

. The lower three formations are sometimes collectively referred to as the Hastings Beds. In

Oxfordshire Oxfordshire is a ceremonial and non-metropolitan county in the north west of South East England. It is a mainly rural county, with its largest settlement being the city of Oxford. The county is a centre of research and development, primaril ...

Buckinghamshire Buckinghamshire (), abbreviated Bucks, is a ceremonial county in South East England that borders Greater London to the south-east, Berkshire to the south, Oxfordshire to the west, Northamptonshire to the north, Bedfordshire to the north-e ...

and

Wiltshire Wiltshire (; abbreviated Wilts) is a historic and ceremonial county in South West England with an area of . It is landlocked and borders the counties of Dorset to the southwest, Somerset to the west, Hampshire to the southeast, Gloucestershire ...

, the Wealden Group is only found as an

outlier In statistics, an outlier is a data point that differs significantly from other observations. An outlier may be due to a variability in the measurement, an indication of novel data, or it may be the result of experimental error; the latter are ...

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 a major eustatic (global) transgression of the sea. The Greensand (

Albian The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/ Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± 0 ...

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.

Palaeontology

The Wealden Group forms outcrops covering a large part of south and south-eastern

including the

Isle of Wight The Isle of Wight ( ) is a county in the English Channel, off the coast of Hampshire, from which it is separated by the Solent. It is the largest and second-most populous island of England. Referred to as 'The Island' by residents, the Is ...

. It takes its name from 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, Sussex and Kent. It has three separate parts: the sandstone "High Weald" in the ...

region of

Kent Kent is a county in South East England and one of the home counties. It borders Greater London to the north-west, Surrey to the west and East Sussex to the south-west, and Essex to the north across the estuary of the River Thames; it faces ...

Sussex Sussex (), from the Old English (), is a historic county in South East England that was formerly an independent medieval Anglo-Saxon kingdom. It is bounded to the west by Hampshire, north by Surrey, northeast by Kent, south by the Englis ...

Surrey Surrey () is a ceremonial county, ceremonial and non-metropolitan county, non-metropolitan counties of England, county in South East England, bordering Greater London to the south west. Surrey has a large rural area, and several significant ur ...

and

Hampshire Hampshire (, ; abbreviated to Hants) is a ceremonial and non-metropolitan county in western South East England on the coast of the English Channel. Home to two major English cities on its south coast, Southampton and Portsmouth, Hampshire ...

. It has yielded many fossils, including

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

s like '' Iguanodon'' and '' Hypsilophodon''.Weishampel ''et al.'' (2004) Apart from fossils, it shows many other signs of being deposited in a continental environment, such as

mudcrack Mudcracks (also known as mud cracks, desiccation cracks or cracked mud) are sedimentary structures formed as muddy sediment dries and contracts.Jackson, J.A., 1997, ''Glossary of Geology'' (4th ed.), American Geological Institute, Alexandria, VA, ...

s and -in some rare cases- dinosaur footprints. Taxa included in the table below have an uncertain provenance and cannot be placed into one of the constituent formations, thus they are placed here.

Pterosaurs

Dinosaurs

Wealden elsewhere in Europe

The term "Wealden" and "Wealden facies" has been applied to other Lower Cretaceous sequences in Europe, including the "German Wealden", comprising the

aged

Bückeberg Formation The Bückeberg Formation is a geologic formation and LagerstätteHornung et al., in Reitner et al., 2013, p.75 in Germany. It preserves fossils dating back to the Berriasian of the Cretaceous period.Hornung et al., 2012 The 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 the Mons Basin, including the

Sainte-Barbe Clays Formation The Sainte-Barbe Clays Formation is a geological formation in Belgium. It is found in localised areas of the northern margin of the Mons Basin, alongside the equivalently aged Hautrage and Baudour Clay Formations. It is Upper Barremian-Lower Apti ...

where large numbers of '' Iguanodon'' were found in the 19th century.

Stratigraphy

Palaeontology

Pterosaurs

Dinosaurs

Wealden elsewhere in Europe

References

Further reading

See also