The Wealden Group, occasionally also referred to as the Wealden Supergroup, is a
group
A group is a number of persons or things that are located, gathered, or classed together.
Groups of people
* Cultural group, a group whose members share the same cultural identity
* Ethnic group, a group whose members share the same ethnic ide ...
(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 ei ...
) in the
lithostratigraphy
Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology.
In general, strata are primarily igneo ...
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 b ...
. 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 ago) ...
to
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 ago), a ...
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
Lower Wick is a small hamlet located in the county of Gloucestershire, England. It is situated about five miles south west of Dursley, eight ...
. 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 of s ...
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 par ...
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 ...
of
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 l ...
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'') a ...
al
coastal plain
A coastal plain is flat, low-lying land adjacent to a sea coast. A fall line commonly marks the border between a coastal plain and a piedmont area. Some of the largest coastal plains are in Alaska and the southeastern United States. The Gulf Coa ...
.
[Jackson (2008)]
The Wealden Group can be found in almost all Early Cretaceous
basins of England: its outcrops curve from the
Wessex Basin
The Wessex Basin is a petroleum-bearing geological area located along the southern coast of England and extending into the English Channel. The onshore part of the basin covers approximately 20,000 km2 and the area that encompasses the Englis ...
in the south to the
Cleveland Basin
The Cleveland Basin is a sedimentary basin in Yorkshire, England. Formed initially by rifting during the Mississippian period of the Early Carboniferous. It is West–East trending and lies between the intrabasinal highs of the Askrigg Block and t ...
in the northeast. It is not found in northwest England and
Wales
Wales ( cy, Cymru ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by England to the Wales–England border, east, the Irish Sea to the north and west, the Celtic Sea to the south west and the ...
, areas which were at the time
tectonic high
A high in structural geology and tectonics an area where tectonic uplift has taken place relative to its surroundings. Highs are often bounded by normal faults and can be regarded as the opposites of basin (geology), basins. A related word is a mas ...
s where no deposition took place. The same is true for the
London Platform around London and
Essex
Essex () is a 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 River Thames to the south, and G ...
. Offshore, the Wealden Group can reach a thickness of 700 metres.
The terms ''Wealden'' and ''Wealden
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 ...
'' 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
The Purbeck Group is an Upper Jurassic to Lower Cretaceous lithostratigraphic group (a sequence of rock strata) 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 ...
, which spans the
Jurassic
The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), 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 J ...
-
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 th ...
boundary. Within the
Wessex Basin
The Wessex Basin is a petroleum-bearing geological area located along the southern coast of England and extending into the English Channel. The onshore part of the basin covers approximately 20,000 km2 and the area that encompasses the Englis ...
, the Wealden Group consists of two
formations: the
Wessex Formation
The Wessex Formation is a fossil-rich English geological formation that dates from the Berriasian to Barremian stages (about 145–125 million years ago) of the Early Cretaceous. It forms part of the Wealden Group and underlies the younger Vecti ...
and overlying
Vectis Formation
The Vectis Formation is a geological formation on the Isle of Wight and Swanage, England whose strata were formed in the lowermost Aptian, approximately 125 million years ago."Magnetostratigraphy of the Lower Cretaceous Vectis Formation (Wealden ...
. In the
Weald Basin
The Weald Basin () is a major topographic feature of the area that is now southern England and northern France from the Triassic to the Late Cretaceous. Its uplift in the Late Cretaceous marked the formation of the Wealden Anticline. The rock str ...
, 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
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.
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, primarily ...
,
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-ea ...
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
The Speeton Clay Formation (SpC)[Speeton Clay Formation]
- Lower Greensand Group
The Lower Greensand Group is a geological unit present across large areas of Southern England. It was deposited during the Aptian and Albian stages of the Early Cretaceous. It predominantly consists of sandstone and unconsolidated sand that were ...
. The difference between these two groups has been formed by a major
eustatic
Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardised g ...
(global)
transgression of the sea. The Greensand (
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 ago), a ...
/
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 ± 0.9 M ...
in age) consists of marine deposits.
The sequence in the Weald Basin has also been described as a
supergroup Supergroup or super group may refer to:
* Supergroup (music), a music group formed by artists who are already notable or respected in their fields
* Supergroup (physics), a generalization of groups, used in the study of supersymmetry
* Supergroup ...
, containing the Weald Clay Group and Hastings Group.
Palaeontology
The Wealden Group forms
outcrop
An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth.
Features
Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficial ...
s covering a large part of south and south-eastern
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 b ...
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 Isle of ...
. 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 English ...
,
Surrey
Surrey () is a ceremonial and non-metropolitan county in South East England, bordering Greater London to the south west. Surrey has a large rural area, and several significant urban areas which form part of the Greater London Built-up Area. ...
and
Hampshire
Hampshire (, ; abbreviated to Hants) is a ceremonial county, ceremonial and non-metropolitan county, non-metropolitan counties of England, county in western South East England on the coast of the English Channel. Home to two major English citi ...
. 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
''Iguanodon'' ( ; meaning 'iguana-tooth'), named in 1825, is a genus of iguanodontian dinosaur. While many species have been classified in the genus ''Iguanodon'', dating from the late Jurassic Period to the early Cretaceous Period of Asia, Eu ...
'' and ''
Hypsilophodon
''Hypsilophodon'' (; meaning "''Hypsilophus''-tooth") is a neornithischian dinosaur genus from the Early Cretaceous period of England. It has traditionally been considered an early member of the group Ornithopoda, but recent research has put thi ...
''.
[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
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 ago) ...
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 Aptian ...
where large numbers of ''
Iguanodon
''Iguanodon'' ( ; meaning 'iguana-tooth'), named in 1825, is a genus of iguanodontian dinosaur. While many species have been classified in the genus ''Iguanodon'', dating from the late Jurassic Period to the early Cretaceous Period of Asia, Eu ...
'' were found in the 19th century.
References
Further reading
*
*
{{refend
See also
*
List of dinosaur-bearing rock formations
This list of dinosaur-bearing rock formations is a list of geologic formations in which dinosaur fossils have been documented.
Containing body fossils
* List of stratigraphic units with dinosaur body fossils
** List of stratigraphic units with few ...
Geological groups of the United Kingdom
Geologic formations of England
Lithostratigraphy of England
Lower Cretaceous Series of Europe
Cretaceous England
Berriasian Stage
Valanginian Stage
Hauterivian Stage
Barremian Stage
Aptian Stage
Shale formations
Sandstone formations