Chalk Group

The Chalk Group (often just called the Chalk) is the lithostratigraphic unit (a certain number of rock strata) which contains the Late Cretaceous limestone succession in southern and eastern England. The same or similar rock sequences occur across the wider northwest European chalk 'province'. It is characterised by thick deposits of chalk, a soft porous white limestone, deposited in a marine environment.

Chalk is a limestone that consists of coccolith biomicrite.[1] A biomicrite is a limestone composed of fossil debris ("bio") and calcium carbonate mud ("micrite"). Most of the fossil debris in chalk consists of the microscopic plates, which are called coccoliths, of microscopic green algae known as coccolithophores. In addition to the coccoliths, the fossil debris includes a variable, but minor, percentage of the fragments of foraminifera, ostracods and mollusks. The coccolithophores lived in the upper part of the water column. When they died, the microscopic calcium carbonate plates, which formed their shells settled downward through the ocean water and accumulated on the ocean bottom to form a thick layer of calcareous ooze, which eventually became the Chalk Group.

The Chalk Group usually shows few signs of bedding, other than lines of flint nodules which become common in the upper part. Nodules of the mineral pyrite also occur and are usually oxidized to brown iron oxide on exposed surfaces.

Well-known outcrops include the White Cliffs of Dover, Beachy Head, the southern coastal cliffs of the Isle of Wight and the quarries and motorway cuttings at Blue Bell Hill, Kent, (which has been classified as a Site of Special Scientific Interest) and at the Stokenchurch Gap on the Oxfordshire/Buckinghamshire border where the M40 motorway cuts through the Aston Rowant National Nature Reserve.

The Needles
The Needles, (Isle of Wight); part of southern England's extensive chalk outcrop.
Fossil Echinoid Echinocorys
Fossil echinoid Echinocorys from the Chalk Group of England
Chalk Group
Stratigraphic range: Cenomanian to Maastrichtian 100–66 Ma
Brass Point (Seven Sister) - geograph.org.uk - 1272999
Brass Point, one of the Seven Sisters
TypeGroup
Sub-unitsCambridge Greensand Grey Chalk Subgroup, White Chalk Subgroup
Underliesunconformity, Thanet Formation, Lambeth Group
OverliesSelborne Group, Hunstanton Formation, Cambridge Greensand
Thicknessover 1,500 m (4,900 ft)
Lithology
Primarylimestone
Othermudstone, flint
Location
CountryEngland
Extentsouthern and eastern England

Subdivisions

The Chalk Group is now divided into a White Chalk Subgroup and a Grey Chalk Subgroup, both of which are further subdivided into formations. These modern divisions replace numerous earlier divisions, references to which occur widely on geological maps and in other geological literature. Previously no subgroups were defined but three formations were identified; the Upper Chalk, Middle Chalk and Lower Chalk. Different formations are defined within the 'northern' and 'southern' provinces, from Norfolk northwards and south of the Thames valley respectively. A 'transitional province' between the two and covering much of East Anglia and the Chiltern Hills is also recognised. A different approach again is taken as regards the succession beneath the North Sea.[2]

Grey Chalk Subgroup

The Grey Chalk Subgroup (formerly the Lower Chalk minus the Plenus Marls) is usually relatively soft and greyish in colour. It is also the most fossiliferous (especially for ammonite fossils). The strata of this subgroup usually begin with the 'Glauconitic Marl Member' (formerly known as the Glauconitic or Chloritic Marl), named after the grains of the green minerals glauconite and chlorite which it contains. The remainder of the subgroup is argillaceous in its lower part (the West Melbury Marly Chalk Formation (formerly the 'Chalk Marl') and becomes progressively purer in the 'Zig-zag Chalk Formation' (the former 'Grey Chalk'). In the central Chilterns the two parts are separated by the hard Totternhoe Stone, which forms a prominent scarp in some places. There are few, if any, flint nodules present.

These two formations are not recognised within the northern province i.e. the outcrop north from East Anglia to Yorkshire, where the entire sequence is now referred to as the 'Ferriby Chalk Formation'. The thickness of the Grey Chalk Subgroup strata varies, averaging around 200 ft (61 m), depending upon the location. They often contains fossils such as the ammonites Schloenbachia, Scaphites, and Mantelliceras, the belemnite Actinocamax, and the bivalves Inoceramus and Ostrea.

Chalk & greensand at Lulworth
Contact between two units of the lithostratigraphy of South England: the Chalk Group (left, white, upper unit) and the Greensand Formation (right, green, lower unit). Location: Lulworth Cove, near West Lulworth, Dorset, England.

White Chalk Subgroup

The White Chalk Subgroup includes what were formerly designated the Middle Chalk and Upper Chalk Formations, together with the Plenus Marls (topmost part of the former Lower Chalk Formation). In the southern province it is divided in the following way (youngest/uppermost at top):

  • Portsdown Chalk Formation (formerly part of 'Upper Chalk' and the equivalent of Rowe Chalk Formation, below)
  • Culver Chalk Formation (formerly part of 'Upper Chalk')
    • Spetisbury Chalk Member (formerly part of 'Upper Chalk')
    • Tarrant Chalk Member (formerly part of 'Upper Chalk')
  • Newhaven Chalk Formation (formerly part of 'Upper Chalk')
  • Seaford Chalk Formation (formerly part of 'Upper Chalk')
  • Lewes Nodular Chalk Formation (formerly part of 'Upper Chalk')
  • New Pit Chalk Formation (formerly part of 'Middle Chalk')
  • Holywell Nodular Chalk Formation (formerly part of 'Middle Chalk')
    • Plenus Marls Member

In the northern province the sequence is divided thus:

  • Rowe Chalk Formation (formerly part of 'Upper Chalk' and the equivalent of Portsdown Chalk Formation, above)
  • Flamborough Chalk Formation (formerly part of 'Upper Chalk')
  • Burnham Chalk Formation (formerly part of 'Upper Chalk')
  • Welton Chalk Formation (formerly 'Middle Chalk')
    • Plenus Marls Member

In the southern province, the former Middle Chalk, now the Holywell Nodular Chalk Formation and overlying New Pit Formation, averages about 200 ft (61 m) in thickness. The sparse fossils found in this sequence include the brachiopod Terebratulina and the echinoid Conulus.

The former Upper Chalk by comparison is softer than the underlying sequence and the flint nodules it contains are far more abundant in the South of England, although in Yorkshire the underlying strata have the highest concentration of flints. It may contain ammonite and gastropod fossils in some nodular layers. The thickness of this sequence varies greatly, often averaging around 300 ft (91 m). Fossils may be abundant and include the bivalve Spondylus, the brachiopods Terebratulina and Gibbithyris, the echinoids Sternotaxis, Micraster, Echinocorys, and Tylocidaris, the crinoid Marsupites, and the small sponge Porosphaera.

The youngest beds of the sequence are found on the coast of Norfolk. Other fossils commonly found in this formation include: solitary corals (such as Parasmilia), marine worm tubes (such as Rotularia), bryozoans, scattered fragments of starfish and fish remains (including shark teeth such as Cretolamna and Squalicorax).

Chalk landscapes of England

The Chalk outcrops across large parts of southern and eastern England and forms a significant number of the major physiographical features. Whilst it has been postulated that a chalk cover was laid down across just about all of England and Wales during Cretaceous times, subsequent uplift and erosion has resulted in it remaining only southeast of a line drawn roughly between The Wash and Lyme Bay in Dorset and eastwards from the scarps of the Lincolnshire and Yorkshire Wolds. Gentle folding of the Mesozoic rocks of this region during the Alpine orogeny has produced the London Basin and the Weald–Artois Anticline, the Hampshire Basin and the less gentle Purbeck-Wight monocline.

The broadly western margin of the Chalk outcrop is marked, from northeast to southwest, to south by the Chalk downlands of the Yorkshire Wolds, the Lincolnshire Wolds, a subdued feature through western Norfolk, including Breckland, the Chiltern Hills, the Berkshire Downs, Marlborough Downs and the western margins of Salisbury Plain and Cranborne Chase and the North and South Dorset Downs.[3] In parts of the Thames Basin and eastern East Anglia the Chalk is concealed by later deposits, as is the case too within the Hampshire Basin.

Ivinghoe Beacon seen from The Ridgeway
Ivinghoe Beacon, Chiltern Hills

Only where the Weald–Artois Anticline has been 'unroofed' by erosion i.e. within the Weald is the Chalk entirely absent. In this area the long south-facing scarp of the North Downs and the longer north-facing scarp of the South Downs face one another across the Weald. For similar reasons, the Chalk is largely absent from the rather smaller area to the south of the Purbeck-Wight Monocline, save for the downs immediately north of Ventnor on the Isle of Wight.

Some of the best exposures of the Chalk are where these ranges intersect the coast to produce dramatic, often vertical cliffs as at Flamborough Head, the White Cliffs of Dover, Seven Sisters, Old Harry Rocks (Purbeck) and The Needles on the Isle of Wight. The Chalk, which once extended across the English Channel, gives rise to similar cliff features on the French coast.

Offshore and elsewhere

Northern Ireland

In the 'Ulster Cretaceous Province' of Northern Ireland the clastic-dominated Hibernian Greensands Group and the overlying Ulster White Limestone Group are the stratigraphical equivalents of the Chalk Group of England. They are best exposed near the Antrim coast.

Scotland

In the 'Scottish Chalk Province' (extending from Mull to Skye) the Inner Hebrides Group is the stratigraphical equivalent of England's Chalk Group. It comprises largely sandstones and mudstones though the Santonian age Gribun Chalk Formation of Mull and nearby Morvern is recognised.

The Low Countries

The Dutch (Dutch: Krijtkalk-Groep) and Belgian (Dutch: Krijt-Groep) equivalents of the Chalk Group are basically continuous and crop out as a slightly northwest dipping monocline in a belt from the German city of Aachen to the city of Mons, where they join Cretaceous deposits of the Paris Basin. North of Namur the Cretaceous is overlain by younger Paleocene and Eocene deposits of the Landen Group.

In the Low Countries, the Chalk Group succession is divided into five formations, from top to base:[4]

In Belgium, the Houthem Formation is sometimes not included in the Chalk Group because it is not a Cretaceous formation. Some stratigraphers therefore prefer to put it in the lower Paleogene Hesbaye Group.

The English Channel

The Channel Tunnel linking England and France was constructed by tunnelling through the West Melbury Marly Chalk (formerly the 'Chalk Marl' - a prominent sub-unit of the Grey Chalk Subgroup).

The North Sea

The chalk is also an important petroleum reservoir in the North Sea Central Graben, mainly in Norwegian and Danish sectors and to a lesser extent in the United Kingdom Continental Shelf sector (UKCS).[5]

Across the north central and northern North Sea, the Chalk Group is a major seal unit, overlying a number of blocks of reservoir rocks and preventing their fluid contents from migrating upwards. North of the line of the Mid-North Sea - Ringkobing - Fyn structural high, the Chalk Group is still recognisable in drilled samples, but becomes increasingly muddy northwards. North of the Beryl Embayment (59°30' N 01°30'E), the Chalk Group is a series of slightly to moderately calcareous mudstones grouped under the name of the Shetland Group. With the exception of some thin sandy units in the inner Moray Firth, this sequence has neither source potential nor reservoir capacity and is not generally considered a drilling target. Its thickness and homogeneity does make it a common target for carrying out directional drilling manoeuvers.

In the Shearwater and Eastern Trough Area Project areas (around 56°30' N 02°30'E, UKCS quadrants 22,23,29 and 30), the Chalk Group can be significantly overpressured. Further south in UKCS quadrant 30 and Norwegian quadrants 1 and 2, this overpressure helps preserve porosity and enables the Chalk to be an effective reservoir.

Reservoir stratigraphy

  • Chalk Unit[6] 6 - Ekofisk formation - Danian age (major reservoir in the Ekofisk oil field and others)
  • Chalk Unit 5 - Tor formation - Maastrichtian age, (major reservoir in many fields including Joanne oil field (UKCS), Valhall oil field (NCS))
  • Chalk Unit 4 - Hod formation - Late Campanian age (mostly non reservoir)
  • Chalk Unit 3 - Hod formation - Santonian to Middle Campanian
  • Chalk Unit 2 - Hod formation - Middle Turonian to Coniacian
  • Turonian shale - Early Turonian (non reservoir)
  • Plenus Marl - Late Cenomanian (non reservoir)
  • Chalk Unit 1 - Hidra Formation - Cenomanian (non reservoir)

Reservoir geology

The majority of Chalk reservoirs are redeposited allochthonous beds. These include debris flows and turbidite flows. Porosities can be very high when preserved from diagenesis by early hydrocarbon charge. However, when these hydrocarbons are produced, diagenesis and compaction can restart which has led to several metres of subsidence at seabed, the collapse of a number of wells, and some extremely expensive remedial work to lift the platforms and re-position them.[5]

See also

References and further reading

  • Hancock, J.M. (1975). The Petrology of the Chalk. London: Proceedings of the Geologists Association, vol 86. pp. 449–535.
  • Lousley, J.E. (1969). Wild Flowers of Chalk and Limestone. London: Collins.
  • Scholle, P.A.; Bedout, D.G.; Moore, C.H. (1983). Carbonate Depositional Environments. American Association of Petroleum Geologist Memoir 33.
  • Smith, A.B.; Batten, D.J. (2002). Fossils of the Chalk (Second ed.). The Palaeontological Association.
  1. ^ As discussed in Chalk Facts by C. S. Harris and Scholle et al. (1983)
  2. ^ Hopson, P.M., 2005 A Stratigraphical Framework for the Upper Cretaceous Chalk of England and Scotland with Statements on the Chalk of Northern Ireland and the UK Offshore Sector, British Geological Survey Research Report RR/05/01 (downloaded from www.bgs.ac.uk)
  3. ^ Ordnance Survey 1:625,000 scale Physical Map of Great Britain sheet 2
  4. ^ Hack, Robert; Azzam, Rafig; Charlier, Robert; 2004: Engineering Geology for Infrastructure Planning in Europe, Lecture Notes in Earth Sciences 104, Springer, ISBN 978-3-540-21075-7, p. 491
  5. ^ a b "The Chalk play of the UK Central Graben" (PDF). Department of Energy and Climate Change. 2006. Archived from the original (PDF) on 18 April 2015. Retrieved 18 April 2015.
  6. ^ Evans, D.; et al. (2003). The Millennium Atlas of the North Sea. Millennium Atlas Co. Chapter 13, Upper Cretaceous, Chalk Group. ISBN 1-86239-119-X.
Alpine orogeny

The Alpine orogeny or Alpide orogeny is an orogenic phase in the Late Mesozoic (Eoalpine) and the current Cenozoic that has formed the mountain ranges of the Alpide belt. These mountains include (from west to east) the Atlas, the Rif, the Baetic Cordillera, the Cantabrian Mountains, the Pyrenees, the Alps, the Apennine Mountains, the Dinaric Alps, the Pindus (Hellenides), the Carpathians, the Balkanides - Balkan Mountains and Rila-Rhodope massifs, the Pontic Mountains, the Taurus, the Armenian Highlands, the Caucasus, the Alborz, the Zagros, the Hindu Kush, the Pamir, the Karakoram, and the Himalayas. Sometimes other names occur to describe the formation of separate mountain ranges: for example Carpathian orogeny for the Carpathians, Hellenic orogeny for the Pindus, Altai orogeny for Altai Mountains or the Himalayan orogeny for the Himalayas.

The Alpine orogeny has also led to the formation of more distant and smaller geological features such as the Weald–Artois Anticline in southern England and northern France, the remains of which can be seen in the chalk ridges of the North and South Downs in southern England. Its effects are particularly visible on the Isle of Wight, where the Chalk Group and overlying Eocene strata are folded to near-vertical, as seen in exposures at Alum Bay and Whitecliff Bay, and on the Dorset coast near Lulworth Cove. Stresses arising from the Alpine orogeny caused the Cenozoic uplift of the Sudetes mountain range and possibly faulted rocks as far away as Öland in southern Sweden during the Paleocene.The Alpine orogeny is caused by the continents Africa and India and the small Cimmerian plate colliding (from the south) with Eurasia in the north. Convergent movements between the tectonic plates (the Indian plate and the African plate from the south, the Eurasian plate from the north, and many smaller plates and microplates) had already begun in the early Cretaceous, but the major phases of mountain building began in the Paleocene to Eocene. The process continues currently in some of the Alpide mountain ranges.

The Alpine orogeny is considered one of the three major phases of orogeny in Europe that define the geology of that continent, along with the Caledonian orogeny that formed the Old Red Sandstone Continent when the continents Baltica and Laurentia collided in the early Paleozoic, and the Hercynian or Variscan orogeny that formed Pangaea when Gondwana and the Old Red Sandstone Continent collided in the middle to late Paleozoic.

Brachauchenius

Brachauchenius (meaning 'short neck') is an extinct genus of pliosaurid that lived in North America (United States) during the Late Cretaceous.

The type species, Brachauchenius lucasi, lived in the Western Inland Sea of North America around 93.5-89.3 million years ago, during the Turonian stage of the Cretaceous. An older specimen from the Barremian of Colombia was considered as part of this genus, representing the first re-occurrence of the non-rhomaleosaurid pliosaurs after a Berriasian-Hauterivian hiatus. However, subsequent analysis of this Colombian specimen shows that it was enough distinctive to warrant a new genus and species, named as Stenorhynchosaurus munozi.The first known (type) specimen (USNM 4989) was collected by Charles Hazelius Sternberg from Ottawa County, Kansas in 1884. It had a skull length of about 90 cm. The species was named by Samuel W. Williston. Brachauchenius represents the last known occurrence of a pliosaur in North America.

A larger specimen (FHSM VP-321 - skull length 170 cm) was collected by George Fryer Sternberg in 1952 from the Fairport Chalk of Russell County, Kansas, and later described by Carpenter. Schumacher and Everhart (2005) reported on the age and locality of both Kansas specimens. This pliosaur is estimated to have been between 6 and 9 meters (about 20 and 30 feet) in length. This specimen was reassigned to its own genus and species, Megacephalosaurus eulerti.In 2013, Benson et al. referred a partial cranium from the Chalk Group of England (previously referred to Polyptychodon) to Brachauchenius indet.

Cambridge Greensand

The Cambridge Greensand is a geological formation in England whose strata date back to the Cenomanian stage of the Late Cretaceous. It forms the transitional bed between the Gault Formation and the Chalk Group in the vicinity of Cambridgeshire, and technically forms the lowest member bed of the West Melbury Marly Chalk Formation. The lithology is made out of glauconitic marl, with a concentration of phosphatic nodules and bones at the base. Dinosaur remains are among the fossils that have been recovered from the formation.

Geography of Dorset

Dorset is a county located in the middle of the south coast of England. It lies between the latitudes 50.512°N and 51.081°N and the longitudes 1.682°W and 2.958°W, and occupies an area of 2,653 km² (1,024 sq mi). It spans 90 kilometres (56 mi) from east to west and 63 kilometres (39 mi) from north to south.

The geology of Dorset is varied; most of the different rocks found in the wider south-east of England outcrop within its boundaries. The oldest rocks (formed in the Early Jurassic epoch) are found in the west of the county; a general progression eastwards reveals younger strata formed in the Middle and Late Jurassic epochs, and the Cretaceous and Paleogene periods. Many of the sea-cliffs in the county, particularly around the town of Lyme Regis, are very rich in exposed fossils.

Dorset's terrain is lowland in nature, albeit hilly in many parts. The highest point in the county is Lewesdon Hill, 279m above sea-level. The landscape of much of the county comprises hills formed by strata of the Chalk Group; these hills include the Dorset Downs (sometimes called the North Dorset Downs), parts of the South Dorset Downs, and the Purbeck Hills. To the north of the Dorset Downs is the Blackmore Vale, a relatively low-lying area of clays and limestones of Jurassic age. The south-east of the county forms part of the Hampshire Basin, an asymmetric syncline covered in sands and gravels of Paleogene age.

The main rivers in the county are the Stour, Frome and Piddle. The Stour is the county's largest river, although its source is in the neighbouring county of Wiltshire. The Frome and Piddle both lie wholly within the county.

The whole of Dorset's coastline is designated part of the Jurassic Coast World Heritage Site, and contains examples of many different coastal landforms, reflecting the variety of the underlying geology. At 191m Golden Cap is the highest cliff on the south coast of England.

The natural resources of Dorset again reflect its particular geology. Western Europe's largest onshore oilfield lies under the south-east of the county. Portland stone and Purbeck limestone have both been quarried for centuries to provide construction material for buildings around the world. Purbeck ball clay is quarried for use in the production of fine pottery.

The predominant land use in Dorset is agriculture. On the chalk hills this is largely arable, whereas in the valleys and vales it is more mixed with pasture. The sand and gravel soils between the towns of Dorchester and Poole were historically covered in heathland, although much of this is now afforested. 53% of the county is designated as being an Area of Outstanding Natural Beauty, and there are 139 Sites Of Special Scientific Interest, covering an area of 199.45 square kilometres (77.01 sq mi).

Dorset is a largely rural county; the county's largest and only major urban area is the South East Dorset conurbation, based on the towns of Poole, Bournemouth and Christchurch, with a combined population of around 400,000. The population of the county overall is 714,900.

The conurbation has a green belt surrounding it to prevent urban sprawl and afford other protections to the wider area.

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.

The county’s chalk has provided a world-class stratigraphic marker giving a great deal of detail in Cretaceous Chalk palaeoecology and palaeontology while in the east of the county on the Kentish border the Dungeness Foreland is important for the study of geomorphology and Holocene sea level fluctuations.

Geology of Hampshire

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.

Geology of the Isle of Wight

The geology of the Isle of Wight is dominated by sedimentary rocks of Cretaceous and Paleogene age. This sequence was affected by the late stages of the Alpine Orogeny, forming the Isle of Wight monocline, the cause of the steeply-dipping outcrops of the Chalk Group and overlying Paleogene strata seen at The Needles, Alum Bay and Whitecliff Bay.

Harwich Formation

The Harwich Formation is a geological formation found in the London Basin of southeastern England. It is Ypresian (early Eocene) in age. It lies unconformably on the Lambeth Group over most of its extent, but may overlie either the Thanet Formation or the Chalk Group to the south. It is overlain by the London Clay Formation.

Hibernian Greensands Group

The Hibernian Greensands Group is a late Cretaceous lithostratigraphic group (a sequence of rock strata) in Northern Ireland. It is Cenomanian to Santonian in age. The name is derived from the characteristically coloured marls and sandstones which occur beneath the chalk particularly along the Antrim coast. The strata are exposed on or near to both the northern and eastern coasts of Antrim and also between Portrush and Dungiven within County Londonderry. Further outcrops occur between Belfast and Lurgan and between Dungannon and Magherafelt. It unconformably overlies a variety of units from the Metamorphic Precambrian Southern Highland Group to the Lower Jurassic Lias. The current names replace an earlier situation where the present group was considered to be a formation and each of the present formations was considered a 'member'. Several other stratigraphic naming schemes were in use during the nineteenth century and much of the twentieth century. Various units were earlier referred to as glauconitic or chloritic marls. This group and the overlying Ulster White Limestone Group are the stratigraphical equivalent of the Chalk Group of southern and eastern England.

Polyptychodon

Polyptychodon (meaning 'shaped fin tooth') is a genus of pliosaurid found Middle-Late Cretaceous marine deposits in southern England. It has been considered a nomen dubium in a 2016 review.

Purbeck Hills

The Purbeck Hills, also called the Purbeck Ridge, are a ridge of chalk downs in Dorset, England. The ridge extends from Lulworth Cove in the west to Old Harry Rocks in the east, where it meets the sea. The hills are part of a system of chalk downlands in southern England formed from the Chalk Group which also includes Salisbury Plain and the South Downs. For most of their length the chalk of the Purbeck Hills is protected from coastal erosion by a band of resistant Portland limestone. Where this band ends, at Durlston Head, the clay and chalk behind has been eroded, creating Poole Bay and the Solent. The ridge of steeply dipping chalk that forms the Purbeck Hills continues further east on the Isle of Wight.

The height of the chalk ridge and proximity to Poole Harbour and the south coast have made the hills of strategic importance. There are a number of Iron Age, Roman and Saxon archaeological sites, such as Nine Barrow Down. At Corfe Castle the hills are broken twice leaving a steep round hill between the ridges on which stood a medieval castle, guarding the only easy route through the hills, until the English Civil War of the 17th century, when it was slighted.

Some of the ridge, around the village of Tyneham, near Lulworth, has been closed to the public for use by the army as a firing range. This has protected them from damage from farming and development, and these areas are now nature reserves. At the eastern end Ballard Down is a National Trust nature reserve which is managed for its calcareous grassland habitat.

Salisbury Plain

Salisbury Plain is a chalk plateau in the south western part of central southern England covering 300 square miles (780 km2). It is part of a system of chalk downlands throughout eastern and southern England formed by the rocks of the Chalk Group and largely lies within the county of Wiltshire, but stretches into Berkshire and Hampshire. The plain is famous for its rich archaeology, including Stonehenge, one of England's best known landmarks. Large areas are given over to military training and thus the sparsely populated plain is the biggest remaining area of calcareous grassland in northwest Europe. Additionally the plain has arable land, and a few small areas of beech trees and coniferous woodland. Its highest point is Easton Hill.

Southerham Works Pit

Southerham Works Pit is a 1-hectare (2.5-acre) geological Site of Special Scientific Interest in Lewes in East Sussex. It is a Geological Conservation Review site.This site exposes layers of the Chalk Group dating to the Upper Cretaceous between 90 and 87 million years ago. It is a key site for understanding the lithostratigraphy of the period and the environments of its chalk sea as well as the evolution and taxonomy of Upper Cretaceous fish.There is access to the southern end of the site from Southerham Lane.

Thanet Formation

The Thanet Formation is a geological formation found in the London Basin of southeastern England. It is of early to mid-Thanetian (late Paleocene) age and gave its name to that stratigraphic interval. It was previously known as the Thanet Beds, the Thanet Sands and the Thanet Sand Formation. It was named after the Isle of Thanet. The type sections are Herne Bay in Kent for the upper part of the formation and Pegwell Bay for the lower part. It lies unconformably on the Late Cretaceous Chalk Group. It unconformably underlies the Lambeth Group, generally the Upnor Formation but in Essex it is the Reading Formation.

Ulster White Limestone Group

The Ulster White Limestone Group is a late Cretaceous lithostratigraphic group (a sequence of rock strata) in Northern Ireland. The name is derived from the characteristic chalk rock which occurs particularly along the Antrim coast. The strata are exposed on or near to both the northern and eastern coasts of Antrim and also between Portrush and Dungiven within County Londonderry. Further outcrops occur between Belfast and Lurgan and between Dungannon and Magherafelt. The current names replace an earlier situation where the present group was considered to be a formation and each of the present formations was considered a 'member'. Several other stratigraphic naming schemes were in use during the nineteenth century and much of the twentieth century. This group and the underlying Hibernian Greensands Group are the stratigraphical equivalent of the Chalk Group of southern and eastern England.

Upnor Formation

The Upnor Formation is a geological formation found in the London Basin of southeastern England. It is of Thanetian (Upper Paleocene) age. It lies unconformably on the Thanet Formation for most of its outcrop, but in the west it lies directly on Chalk Group. It is generally overlain either by the Reading Formation or the Woolwich Formation, but locally in north and east Kent it is overlain unconformably by the Harwich Formation. It forms the lowermost part of the Lambeth Group. The type section is at Lower Upnor Pit, north Kent.

Upper Greensand Formation

The Upper Greensand Formation is a Cretaceous formation of Albian to Cenomanian in age. It is found within the Wessex Basin and parts of the Weald Basin in southern England. It overlies the Gault Clay and underlies the Chalk Group. It varies in thickness from zero to 75 m. It is predominantly a glauconitic fine-grained sandstone, locally becoming silty.

Woodside, Bedfordshire

Woodside is a hamlet located in the Central Bedfordshire district of Bedfordshire, England.

Located at the junction of Woodside Road and Grove Road, Woodside stands 546 feet above sea level. The underlying geology is a Chalk Group known as Lewes Nodular Chalk Formation and Seaford Chalk Formation which was deposited between 84 and 94 million years ago in the Cretaceous Period. The superficial geology is clay with flints, deposited in the Quaternary and Neogene Periods.It is probable that the settlement was established in the early Middle Ages through clearing the northern end of Caddington Wood by squatters seeking land outside Caddington Manor (hence the name "Woodside" and its linear shape). Most of the settlement stands on higher ground between two parallel valleys. The squatter development of Woodside continued into the sixteenth and seventeenth centuries.A Baptist Church was established in the settlement in 1862, while St Andrew's Anglican Church was established in Woodside as the "Slip End Mission Church" in 1878.Today, Woodside forms part of the Slip End (where the 2011 Civil Parish population was included) civil parish, and is located directly southwest of the M1 motorway. The motorway acts as the border between Woodside and the large town of Luton.

Languages

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.