Bracklesham Group

Last updated

Bracklesham Group
Stratigraphic range: Eocene
Branksome Sand (geograph 4084855).jpg
Branksome Sand Formation at the top of the Bracklesham Group, made up of white, yellow, rose-coloured and crimson sands with laminated pipe clay. Alum Bay cliffs.
Type Group
Sub-units
Underlies Barton Group
Overlies Thames Group
Thickness~120 m Hampshire Basin, ~140 m London Basin
Lithology
Primary clay, silt & sand
Location
Region Hampshire Basin, London Basin, England
Country United Kingdom
Type section
Named for Bracklesham

The Bracklesham Group (formerly Bracklesham Beds), in geology, is a series of clays and marls, with sandy and lignitic beds, in the middle Eocene of the Hampshire Basin and London Basin of England. [1]

The type section of the Bracklesham Group is the sea cliffs at Whitecliff Bay on the Isle of Wight, and it is also well developed on the mainland. The Group gets its name from a section at Bracklesham in Sussex. The thickness of the deposit is around 120 m. [1] Fossil mollusca are abundant, and fossil fish are to be found, as well as Palaeophis , a sea-snake, and Puppigerus , a sea turtle. Nummulites and other foraminifera also occur.

The Bracklesham Group lies between the Barton Clay above and the Bournemouth Beds,[ citation needed ] Lower Bagshot, below. In the London Basin, these beds are represented only by thin sandy clays in the Middle Bagshot group. In the Paris Basin the "Calcaire grossier" lies upon the same geological horizon.

Related Research Articles

London Clay Marine geological formation

The London Clay Formation is a marine geological formation of Ypresian age which crops out in the southeast of England. The London Clay is well known for its fossil content. The fossils from the lower Eocene rocks indicate a moderately warm climate, the tropical or subtropical flora. Though sea levels changed during the deposition of the clay, the habitat was generally a lush forest – perhaps like in Indonesia or East Africa today – bordering a warm, shallow ocean.

Greensand

Greensand or green sand is a sand or sandstone which has a greenish color. This term is specifically applied to shallow marine sediment that contains noticeable quantities of rounded greenish grains. These grains are called glauconies and consist of a mixture of mixed-layer clay minerals, such as smectite and glauconite mica. Greensand is also loosely applied to any glauconitic sediment.

Gault

The Gault Formation is a geological formation of stiff blue clay deposited in a calm, fairly deep-water marine environment during the Lower Cretaceous Period. It is well exposed in the coastal cliffs at Copt Point in Folkestone, Kent, England, where it overlays the Lower Greensand formation, and underlies the Upper Greensand Formation. These represent different facies, with the sandier parts probably being deposited close to the shore and the clay in quieter water further from the source of sediment; both are believed to be shallow-water deposits.

Geology of Dorset

Dorset is a county in South West England on the English Channel coast. Covering an area of 2,653 square kilometres (1,024 sq mi); it borders Devon to the west, Somerset to the north-west, Wiltshire to the north-east, and Hampshire to the east. The great variation in its landscape owes much to the underlying geology, which includes an almost unbroken sequence of rocks from 200 to 40 million years ago (Mya) and superficial deposits from 2 Mya to the present. In general, the oldest rocks appear in the far west of the county, with the most recent (Eocene) in the far east. Jurassic rocks also underlie the Blackmore Vale and comprise much of the coastal cliff in the west and south of the county; although younger Cretaceous rocks crown some of the highpoints in the west, they are mainly to be found in the centre and east of the county.

The geology of Hampshire in southern England broadly comprises a gently folded succession of sedimentary rocks dating from the Cretaceous and Palaeogene periods. The lower (early) Cretaceous rocks are sandstones and mudstones whilst those of the upper (late) Cretaceous are the various formations which comprise the Chalk Group and give rise to the county's downlands. Overlying these rocks are the less consolidated Palaeogene clays, sands, gravels and silts of the Lambeth, Thames and Bracklesham Groups which characterise the Hampshire Basin.

Bracklesham Bay Bay in West Sussex, United Kingdom

Bracklesham Bay is a 200.6-hectare (496-acre) biological and geological Site of Special Scientific Interest in West Sussex. It is a Geological Conservation Review site.

In geology, the Bagshot Beds are a series of sands and clays of shallow-water origin, some being fresh-water, some marine. They belong to the upper Eocene formation of the London and Hampshire basins, in England and derive their name from Bagshot Heath in Surrey. They are also well developed in Hampshire, Berkshire and the Isle of Wight. The following divisions are generally accepted:

Barton Beds

Barton Beds is the name given to a series of grey and brown clays, with layers of sand, of Upper Eocene age, which are found in the Hampshire Basin of southern England. They are particularly well exposed in the cliffs at Barton-on-Sea, which is the type locality for the Barton Beds, and lends its name to the Bartonian age of the Eocene epoch. The clay is abundant in fossils, especially molluscs.

Purbeck Group

The Purbeck Group is an Upper Jurassic to Lower Cretaceous lithostratigraphic group 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 the cliffs west of Swanage.

Wealden Group

The Wealden Group, occasionally also referred to as the Wealden Supergroup, is a group 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 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.

Clement Reid

Clement Reid FRS was a British geologist and palaeobotanist.

Geology of London

The geology of London comprises various differing layers of sedimentary rock upon which London, England is built.

London Basin

The London Basin is an elongated, roughly triangular sedimentary basin approximately 250 kilometres (160 mi) long which underlies London and a large area of south east England, south eastern East Anglia and the adjacent North Sea. The basin formed as a result of compressional tectonics related to the Alpine orogeny during the Palaeogene period and was mainly active between 40 and 60 million years ago.

Hampshire Basin

The Hampshire Basin is a geological basin of Palaeogene age in southern England, underlying parts of Hampshire, the Isle of Wight, Dorset, and Sussex. Like the London Basin to the northeast, it is filled with sands and clays of Paleocene and younger ages and it is surrounded by a broken rim of chalk hills of Cretaceous age.

Whitecliff Bay and Bembridge Ledges is a 131.6-hectare (325-acre) Site of Special Scientific Interest that lies around the coastline of the easternmost part of the Isle of Wight from the Bembridge harbour entrance in the north around Foreland to Whitecliff Bay to the south. The site was notified in 1955 for both its biological and geological features.

Geology of East Sussex Overview of the geology of East Sussex

The geology of East Sussex is defined by the Weald–Artois anticline, a 60 kilometres (37 mi) wide and 100 kilometres (62 mi) long fold within which caused the arching up of the chalk into a broad dome within the middle Miocene, which has subsequently been eroded to reveal a lower Cretaceous to Upper Jurassic stratigraphy. East Sussex is best known geologically for the identification of the first dinosaur by Gideon Mantell, near Cuckfield, to the famous hoax of the Piltdown man near Uckfield.

Homarus morrisi is a species of fossil lobster from the Eocene of southern England.

The Bouldnor Formation is a geological formation in the Hampshire Basin of southern England. It is the youngest formation of the Solent Group and was deposited during the uppermost Eocene and lower Oligocene.

Thames Group

The Thames Group is an Eocene lithostratigraphic group which is widespread in southeast England, especially in the Hampshire Basin from Dorset through Hampshire to West Sussex and in the Isle of Wight and in the London Basin from Berkshire east through northern Hampshire, Surrey and Greater London to Essex and north Kent. It is encountered in older literature as the London Clay Group.

Marjorie Chandler (1897–1983) was a British paleobotanist who made her own reputation as a scientist after a long partnership with Eleanor Mary Reid, as a research assistant.

References

  1. 1 2 "Bracklesham Group". BGS Lexicon of Named Rock Units. Retrieved 8 June 2013.
Attribution