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118-598: The South Downs are a range of chalk hills in the south-eastern coastal counties of England that extends for about 260 sq mi (670 km) across the south-eastern coastal counties of England from the Itchen valley of Hampshire in the west to Beachy Head , in the Eastbourne Downland Estate , East Sussex, in the east. The Downs are bounded on the northern side by a steep escarpment , from whose crest there are extensive views northwards across

236-530: A shallow sea which extended across much of northwest Europe. The rock is composed of the microscopic skeletons of plankton which lived in the sea, hence its colour. The chalk has many fossils , and bands of flint occur throughout the formation. The Chalk is divided into the Lower, Middle and Upper Chalk, a thin band of cream-coloured nodular chalk known as the Melbourn Rock marking the boundary between

354-555: A Berriasian–Barremian warm-dry phase, an Aptian–Santonian warm-wet phase, and a Campanian–Maastrichtian cool-dry phase. As in the Cenozoic, the 400,000 year eccentricity cycle was the dominant orbital cycle governing carbon flux between different reservoirs and influencing global climate. The location of the Intertropical Convergence Zone (ITCZ) was roughly the same as in the present. The cooling trend of

472-487: A book called The Invisible Man in 1898, and in it says "He fled to South Down". Chalk Chalk is a soft, white, porous , sedimentary carbonate rock . It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton that had settled to the sea floor . Chalk is common throughout Western Europe , where deposits underlie parts of France, and steep cliffs are often seen where they meet

590-550: A few are more recent. A mixture of chalk and mercury can be used as fingerprint powder . However, because of the toxicity of the mercury, the use of such mixtures for fingerprinting was abandoned in 1967. Cretaceous Period The Cretaceous was a period with a relatively warm climate , resulting in high eustatic sea levels that created numerous shallow inland seas . These oceans and seas were populated with now- extinct marine reptiles , ammonites , and rudists , while dinosaurs continued to dominate on land. The world

708-615: A geologic signature associated with the mass extinction that lies between the Mesozoic and Cenozoic Eras . The Cretaceous as a separate period was first defined by Belgian geologist Jean d'Omalius d'Halloy in 1822 as the Terrain Crétacé , using strata in the Paris Basin and named for the extensive beds of chalk ( calcium carbonate deposited by the shells of marine invertebrates , principally coccoliths ), found in

826-691: A lowland grassland on the west and south facing scarp slopes of the Meon valley; and Beacon Hill, a high quality chalk grassland 5 km west of Old Winchester Hill. In 1923 the Society of Sussex Downsmen (now the South Downs Society) was formed with the aim of protecting the area's unique landscape. The South Downs are a popular area for ramblers with a network of over 2,000 mi (3,200 km) of well-managed, well-signed and easily accessible trails. The principal bridleway, and longest of them,

944-735: A poem "On the South Downs". The South Downs have been home to several writers, including Jane Austen who lived at Chawton on the edge of the Downs in Hampshire. The Bloomsbury Group often visited Monk's House in Rodmell , the home of Virginia Woolf in the Ouse valley. Alfred, Lord Tennyson , had a second home at Aldworth, on Blackdown ; geologically part of the Weald , Blackdown lies north of

1062-674: A straight shell, flourished in the seas along with reef-building rudist clams. Inoceramids were also particularly notable among Cretaceous bivalves, and they have been used to identify major biotic turnovers such as at the Turonian-Coniacian boundary. Predatory gastropods with drilling habits were widespread. Globotruncanid foraminifera and echinoderms such as sea urchins and starfish (sea stars) thrived. Ostracods were abundant in Cretaceous marine settings; ostracod species characterised by high male sexual investment had

1180-459: A whole, although there has been large-scale urban encroachment onto the chalk downland by major seaside resorts, including most notably Brighton and Hove . The South Downs have been inhabited since ancient times and at periods the area has supported a large population, particularly during Romano-British times. There is a rich heritage of historical features and archaeological remains, including defensive sites, burial mounds and field boundaries. Within

1298-564: A ~0.6 °C increase in temperature. The latter warming interval, occurring at the very end of the Cretaceous, was triggered by the activity of the Deccan Traps. The LKEPCI lasted into the Late Palaeocene , when it gave way to another supergreenhouse interval. The production of large quantities of magma, variously attributed to mantle plumes or to extensional tectonics , further pushed sea levels up, so that large areas of

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1416-642: Is mined from chalk deposits both above ground and underground . Chalk mining boomed during the Industrial Revolution , due to the need for chalk products such as quicklime and bricks . Most people first encounter chalk in school where it refers to blackboard chalk , which was originally made of mineral chalk, since it readily crumbles and leaves particles that stick loosely to rough surfaces, allowing it to make writing that can be readily erased. Blackboard chalk manufacturers now may use mineral chalk, other mineral sources of calcium carbonate, or

1534-589: Is 271 m (889 ft) above sea level. The plateau-like top of this irregularly shaped hill, which lies just south of Petersfield, Hampshire , was in regular use through prehistory. It has been designated as a national nature reserve . Within the boundary of the South Downs National Park, which includes parts of the western Weald to the north of the South Downs, the highest point is Blackdown , West Sussex, which rises to 280 m (919 ft) above sea level. However, Blackdown geologically

1652-610: Is a fine-textured, earthy type of limestone distinguished by its light colour, softness, and high porosity. It is composed mostly of tiny fragments of the calcite shells or skeletons of plankton , such as foraminifera or coccolithophores . These fragments mostly take the form of calcite plates ranging from 0.5 to 4 microns in size, though about 10% to 25% of a typical chalk is composed of fragments that are 10 to 100 microns in size. The larger fragments include intact plankton skeletons and skeletal fragments of larger organisms, such as molluscs , echinoderms , or bryozoans . Chalk

1770-466: Is about a case that Holmes solves whilst living there. The author Graham Greene 's first published novel, The Man Within (1929), is set largely on and around the South Downs. The book's principal character, Andrews, travels by foot across the Downs to reach Lewes and attend the Assizes. Greene provides a detailed description of both the landscape and its 'feel'. The author H. G. Wells published

1888-663: Is also a war memorial , The Chattri , dedicated to Indian soldiers who died in the Brighton area, having been brought there for treatment after being injured fighting on the Western Front in the First World War . Rudyard Kipling who lived in Rottingdean described the South Downs as "Our blunt, bow-headed whale-backed Downs". Writing in 1920 in his poem The South Country , poet Hilaire Belloc describes

2006-508: Is also the only form of limestone that commonly shows signs of compaction. Flint (a type of chert ) is very common as bands parallel to the bedding or as nodules in seams , or linings to fractures , embedded in chalk. It is probably derived from sponge spicules or other siliceous organisms as water is expelled upwards during compaction. Flint is often deposited around larger fossils such as Echinoidea which may be silicified (i.e. replaced molecule by molecule by flint). Chalk

2124-428: Is applied to the hands and feet to remove perspiration and reduce slipping. Chalk may also be used as a house construction material instead of brick or wattle and daub : quarried chalk was cut into blocks and used as ashlar , or loose chalk was rammed into blocks and laid in mortar. There are still houses standing which have been constructed using chalk as the main building material. Most are pre- Victorian though

2242-518: Is commonly used as a drying agent to obtain better grip by gymnasts and rock climbers. Glazing putty mainly contains chalk as a filler in linseed oil . Chalk and other forms of limestone may be used for their properties as a base . Chalk is a source of quicklime by thermal decomposition , or slaked lime following quenching of quicklime with water. In agriculture , chalk is used for raising pH in soils with high acidity . Small doses of chalk can also be used as an antacid . Additionally,

2360-619: Is found in England, northern France, the low countries , northern Germany , Denmark and in the subsurface of the southern part of the North Sea . Chalk is not easily consolidated and the Chalk Group still consists of loose sediments in many places. The group also has other limestones and arenites . Among the fossils it contains are sea urchins , belemnites , ammonites and sea reptiles such as Mosasaurus . In southern Europe,

2478-472: Is not part of the South Downs but instead forms part of the Greensand Ridge on the Weald 's western margins. A list of those points on the South Downs above 700 ft (210 m), going from west to east, is given below. Archaeological evidence has revealed that the Downs have been inhabited and utilised for thousands of years. Neolithic flint mines such as Cissbury , burial mounds such as

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2596-526: Is now usually made of talc (magnesium silicate). Chalk beds form important petroleum reservoirs in the North Sea and along the Gulf Coast of North America. In southeast England, deneholes are a notable example of ancient chalk pits. Such bell pits may also mark the sites of ancient flint mines, where the prime object was to remove flint nodules for stone tool manufacture. The surface remains at Cissbury are one such example, but perhaps

2714-545: Is so common in Cretaceous marine beds that the Cretaceous Period was named for these deposits. The name Cretaceous was derived from Latin creta , meaning chalk . Some deposits of chalk were formed after the Cretaceous. The Chalk Group is a European stratigraphic unit deposited during the late Cretaceous Period. It forms the famous White Cliffs of Dover in Kent , England, as well as their counterparts of

2832-592: Is the South Downs Way . The Monarch's Way , having originated at Worcester , crosses the South Downs and ends at Shoreham-by-Sea . Sports undertaken on the Downs include paragliding , mountain-biking , horse riding and walking . The popular Beachy Head Marathon (formerly Seven Sisters Marathon ), a hilly cross-country marathon, takes place each autumn on the eastern Downs, starting and finishing in Eastbourne. The South Downs Trail Marathon starts in

2950-401: Is typically almost pure calcite, CaCO 3 , with just 2% to 4% of other minerals. These are usually quartz and clay minerals , though collophane (cryptocrystalline apatite , a phosphate mineral) is also sometimes present, as nodules or as small pellets interpreted as fecal pellets. In some chalk beds, the calcite has been converted to dolomite , CaMg(CO 3 ) 2 , and in a few cases

3068-752: The Cap Blanc Nez on the other side of the Dover Strait . The Champagne region of France is mostly underlain by chalk deposits, which contain artificial caves used for wine storage . Some of the highest chalk cliffs in the world occur at Jasmund National Park in Germany and at Møns Klint in Denmark . Chalk deposits are also found in Cretaceous beds on other continents, such as the Austin Chalk , Selma Group , and Niobrara Formations of

3186-462: The Devil's Jumps and Devil's Humps , and hill forts like Chanctonbury Ring are strong features in the landscape. It has been estimated that the tree cover of the Downs was cleared over 3000 years ago, and the present closely grazed turf is the result of continual grazing by sheep. Proposals to create a national park for the South Downs date back to the 1940s. However, it was not until 1999 that

3304-713: The Mancos Shale of western North America. These shales are an important source rock for oil and gas , for example in the subsurface of the North Sea. In northwestern Europe, chalk deposits from the Upper Cretaceous are characteristic for the Chalk Group , which forms the white cliffs of Dover on the south coast of England and similar cliffs on the French Normandian coast. The group

3422-711: The North American Cordillera , as the Nevadan orogeny was followed by the Sevier and Laramide orogenies . Gondwana had begun to break up during the Jurassic Period, but its fragmentation accelerated during the Cretaceous and was largely complete by the end of the period. South America , Antarctica , and Australia rifted away from Africa (though India and Madagascar remained attached to each other until around 80 million years ago); thus,

3540-545: The North Downs as its counterpart on the northern side, as shown on the diagram. Between these two escarpments the anticline has been subject to differential erosion so that geologically distinct areas of hills and vales lie in roughly concentric circles towards the centre; these comprise the Greensand Ridge , most prominent on the north side of the Weald, where it includes Leith Hill , the highest hill in south-east England,

3658-503: The Second World War to increase domestic food production – which continued into the 1950s - much grassland was ploughed up for arable farming, fundamentally changing the landscape and ecology, with the loss of much biodiversity. As a result, while old chalk grassland accounted for 40-50% of the eastern Downs before the war, only 3-4% survives. This and development pressures from the surrounding population centres ultimately led to

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3776-553: The Selli Event . Early Aptian tropical sea surface temperatures (SSTs) were 27–32 °C, based on TEX 86 measurements from the equatorial Pacific. During the Aptian, Milankovitch cycles governed the occurrence of anoxic events by modulating the intensity of the hydrological cycle and terrestrial runoff. The early Aptian was also notable for its millennial scale hyperarid events in the mid-latitudes of Asia. The BAWI itself

3894-750: The Sussex Downs . The Western Downs, lying west of the River Arun , are much more wooded, particularly on the scarp face, than the Eastern Downs. The bare Eastern Downs – the only part of the chalk escarpment to which, until the late 19th century, the term "South Downs" was usually applied – have come to epitomise, in literature and art, the South Downs as a whole and which have been the subject matter of such celebrated writers and artists as Rudyard Kipling (the "blunt, bow-headed, whale-backed downs") and Eric Ravilious . Four river valleys cut through

4012-728: The Turonian Age, based on isotopic evidence. However, this has subsequently been suggested to be the result of inconsistent isotopic proxies, with evidence of polar rainforests during this time interval at 82° S. Rafting by ice of stones into marine environments occurred during much of the Cretaceous, but evidence of deposition directly from glaciers is limited to the Early Cretaceous of the Eromanga Basin in southern Australia . Flowering plants (angiosperms) make up around 90% of living plant species today. Prior to

4130-500: The Weald . The South Downs National Park forms a much larger area than the chalk range of the South Downs, and includes large parts of the Weald. The South Downs are characterised by rolling chalk downland with close-cropped turf and dry valleys , and are recognised as one of the most important chalk landscapes in England. The range is one of the four main areas of chalk downland in southern England . The South Downs are relatively less populated compared to South East England as

4248-483: The tuatara ) disappeared from North America and Europe after the Early Cretaceous , and were absent from North Africa and northern South America by the early Late Cretaceous . The cause of the decline of Rhynchocephalia remains unclear, but has often been suggested to be due to competition with advanced lizards and mammals. They appear to have remained diverse in high-latitude southern South America during

4366-999: The Albian regularly expanded northward in tandem with expansions of subtropical high pressure belts. The Cedar Mountain Formation's Soap Wash flora indicates a mean annual temperature of between 19 and 26 °C in Utah at the Albian-Cenomanian boundary. Tropical SSTs during the Cenomanian-Turonian Thermal Maximum were at least 30 °C, though one study estimated them as high as between 33 and 42 °C. An intermediate estimate of ~33-34 °C has also been given. Meanwhile, deep ocean temperatures were as much as 15 to 20 °C (27 to 36 °F) warmer than today's; one study estimated that deep ocean temperatures were between 12 and 20 °C during

4484-486: The Cenomanian between the Albian and Turonian. The Cretaceous is divided into Early and Late Cretaceous epochs , or Lower and Upper Cretaceous series . In older literature, the Cretaceous is sometimes divided into three series: Neocomian (lower/early), Gallic (middle) and Senonian (upper/late). A subdivision into 12 stages , all originating from European stratigraphy, is now used worldwide. In many parts of

4602-571: The Cenozoic Era   —   the ichthyosaurs , last remaining temnospondyls ( Koolasuchus ), and nonmammalian cynodonts ( Tritylodontidae )   —   were already extinct millions of years before the event occurred. Coccolithophorids and molluscs , including ammonites , rudists , freshwater snails , and mussels , as well as organisms whose food chain included these shell builders, became extinct or suffered heavy losses. For example, ammonites are thought to have been

4720-645: The Coniacian through the Maastrichtian. During the Cretaceous, the late- Paleozoic -to-early-Mesozoic supercontinent of Pangaea completed its tectonic breakup into the present-day continents , although their positions were substantially different at the time. As the Atlantic Ocean widened, the convergent-margin mountain building ( orogenies ) that had begun during the Jurassic continued in

4838-626: The Cretaceous is sharply defined, being placed at an iridium -rich layer found worldwide that is believed to be associated with the Chicxulub impact crater , with its boundaries circumscribing parts of the Yucatán Peninsula and extending into the Gulf of Mexico . This layer has been dated at 66.043 Mya. At the end of the Cretaceous, the impact of a large body with the Earth may have been

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4956-570: The Cretaceous is usually a marine system consisting of competent limestone beds or incompetent marls . Because the Alpine mountain chains did not yet exist in the Cretaceous, these deposits formed on the southern edge of the European continental shelf , at the margin of the Tethys Ocean . During the Cretaceous, the present North American continent was isolated from the other continents. In

5074-537: The Cretaceous seas. Stagnation of deep sea currents in middle Cretaceous times caused anoxic conditions in the sea water leaving the deposited organic matter undecomposed. Half of the world's petroleum reserves were laid down at this time in the anoxic conditions of what would become the Persian Gulf and the Gulf of Mexico. In many places around the world, dark anoxic shales were formed during this interval, such as

5192-672: The Jurassic, the North Atlantic already opened, leaving a proto-ocean between Europe and North America. From north to south across the continent, the Western Interior Seaway started forming. This inland sea separated the elevated areas of Laramidia in the west and Appalachia in the east. Three dinosaur clades found in Laramidia (troodontids, therizinosaurids and oviraptorosaurs) are absent from Appalachia from

5310-576: The LKEPCI. During this period of relatively cool temperatures, the ITCZ became narrower, while the strength of both summer and winter monsoons in East Asia was directly correlated to atmospheric CO 2 concentrations. Laramidia likewise had a seasonal, monsoonal climate. The Maastrichtian was a time of chaotic, highly variable climate. Two upticks in global temperatures are known to have occurred during

5428-532: The Late Cretaceous, where lizards remained rare, with their remains outnumbering terrestrial lizards 200:1. Choristoderes , a group of freshwater aquatic reptiles that first appeared during the preceding Jurassic, underwent a major evolutionary radiation in Asia during the Early Cretaceous, which represents the high point of choristoderan diversity, including long necked forms such as Hyphalosaurus and

5546-555: The Late Cretaceous-Early Palaeogene Cool Interval (LKEPCI). Tropical SSTs declined from around 35 °C in the early Campanian to around 28 °C in the Maastrichtian. Deep ocean temperatures declined to 9 to 12 °C, though the shallow temperature gradient between tropical and polar seas remained. Regional conditions in the Western Interior Seaway changed little between the MKH and

5664-596: The Lower and Middle units. The strata of southeast England, including the Chalk, were gently folded during a phase of the Alpine Orogeny to produce the Weald-Artois Anticline , a dome-like structure with a long east-west axis. Erosion has removed the central part of the dome, leaving the north-facing escarpment of the South Downs along its southern margin with the south-facing chalk escarpment of

5782-628: The MKH. Mean annual temperatures at the poles during the MKH exceeded 14 °C. Such hot temperatures during the MKH resulted in a very gentle temperature gradient from the equator to the poles; the latitudinal temperature gradient during the Cenomanian-Turonian Thermal Maximum was 0.54 °C per ° latitude for the Southern Hemisphere and 0.49 °C per ° latitude for the Northern Hemisphere, in contrast to present day values of 1.07 and 0.69 °C per ° latitude for

5900-412: The MKH. The poles were so warm that ectothermic reptiles were able to inhabit them. Beginning in the Santonian, near the end of the MKH, the global climate began to cool, with this cooling trend continuing across the Campanian. This period of cooling, driven by falling levels of atmospheric carbon dioxide, caused the end of the MKH and the transition into a cooler climatic interval, known formally as

6018-404: The Maastrichtian, bucking the trend of overall cooler temperatures during the LKEPCI. Between 70 and 69 Ma and 66–65 Ma, isotopic ratios indicate elevated atmospheric CO 2 pressures with levels of 1000–1400 ppmV and mean annual temperatures in west Texas between 21 and 23 °C (70 and 73 °F). Atmospheric CO 2 and temperature relations indicate a doubling of pCO 2 was accompanied by

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6136-428: The Mesozoic) ended with the Cretaceous–Paleogene extinction event , a large mass extinction in which many groups, including non-avian dinosaurs, pterosaurs , and large marine reptiles , died out, widely thought to have been caused by the impact of a large asteroid that formed the Chicxulub crater in the Gulf of Mexico. The end of the Cretaceous is defined by the abrupt Cretaceous–Paleogene boundary (K–Pg boundary),

6254-418: The North American interior. Chalk is also found in western Egypt (Khoman Formation) and western Australia ( Miria Formation ). Chalk of Oligocene to Neogene age has been found in drill cores of rock under the Pacific Ocean at Stewart Arch in the Solomon Islands . There are layers of chalk, containing Globorotalia , in the Nicosia Formation of Cyprus , which formed during the Pliocene . Chalk

6372-419: The South Atlantic and Indian Oceans were newly formed. Such active rifting lifted great undersea mountain chains along the welts, raising eustatic sea levels worldwide. To the north of Africa the Tethys Sea continued to narrow. During most of the Late Cretaceous, North America would be divided in two by the Western Interior Seaway , a large interior sea, separating Laramidia to the west and Appalachia to

6490-402: The South Downs Environmentally Sensitive Area there are thirty-seven Sites of Special Scientific Interest , including large areas of chalk grassland. The grazing of sheep on the thin, well-drained chalk soils of the Downs over many centuries, and browsing by rabbits, resulted in the fine, short, springy turf, known as old chalk grassland , that has come to epitomise the South Downs today. Until

6608-450: The South Downs as "the great hills of the South Country". In On The South Coast , poet Algernon Charles Swinburne describes the South Downs as "the green smooth-swelling unending downs". The naturalist-writer William Henry Hudson wrote that "during the whole fifty-three mile length from Beachy Head to Harting the ground never rises above a height of 850 feet, but we feel on top of the world". Poet Francis William Bourdillon also wrote

6726-405: The South Downs but is included in the South Downs National Park. In the introduction to Arthur Conan Doyle 's short story collection His Last Bow , Dr. Watson states that Sherlock Holmes has retired to a small farm upon the Downs near Eastbourne. In the story "His Last Bow" itself, Holmes states that he "lives and keeps bees upon the South Downs". Furthermore, the short story " The Lion's Mane "

6844-445: The South Downs presents itself as a steep wall that bounds the horizon, with its grassland heights punctuated with clumps of trees (such as Chanctonbury Ring ). In the west, the chalk ridge of the South Downs merges with the North Downs to form the Hampshire Downs . In the east, the escarpment terminates at the English Channel coast between Seaford and Eastbourne , where it produces the spectacular white cliffs of Seaford Head ,

6962-414: The South Downs, namely those of the rivers Arun, Adur , Ouse and Cuckmere , providing a contrasting landscape. Chalk aquifers and to a lesser extent winterbourne streams supply much of the water required by the surrounding settlements. Dew ponds , artificial ponds for watering livestock, are a characteristic feature on the downland. The highest point on the South Downs is Butser Hill , whose summit

7080-514: The Southern and Northern hemispheres, respectively. This meant weaker global winds, which drive the ocean currents, and resulted in less upwelling and more stagnant oceans than today. This is evidenced by widespread black shale deposition and frequent anoxic events . Tropical SSTs during the late Albian most likely averaged around 30 °C. Despite this high SST, seawater was not hypersaline at this time, as this would have required significantly higher temperatures still. On land, arid zones in

7198-403: The Tethys to the Arctic Ocean and enabling biotic exchange between the two oceans. At the peak of the Cretaceous transgression , one-third of Earth's present land area was submerged. The Cretaceous is justly famous for its chalk ; indeed, more chalk formed in the Cretaceous than in any other period in the Phanerozoic . Mid-ocean ridge activity—or rather, the circulation of seawater through

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7316-425: The ancestors of modern-day birds also diversified. They inhabited every continent, and were even found in cold polar latitudes. Pterosaurs were common in the early and middle Cretaceous, but as the Cretaceous proceeded they declined for poorly understood reasons (once thought to be due to competition with early birds , but now it is understood avian adaptive radiation is not consistent with pterosaur decline ). By

7434-548: The chalk came mostly form low-magnesium calcite skeletons, so the sediments were already in the form of highly stable low-magnesium calcite when deposited. This is in contrast with most other limestones, which formed from high-magnesium calcite or aragonite that rapidly converted to the more stable low-magnesium calcite after deposition, resulting in the early cementation of such limestones. In chalk, absence of this calcium carbonate conversion process prevented early cementation, which partially accounts for chalk's high porosity. Chalk

7552-408: The continental crust were covered with shallow seas. The Tethys Sea connecting the tropical oceans east to west also helped to warm the global climate. Warm-adapted plant fossils are known from localities as far north as Alaska and Greenland , while dinosaur fossils have been found within 15 degrees of the Cretaceous south pole . It was suggested that there was Antarctic marine glaciation in

7670-472: The cross-section of dry valleys known as the Seven Sisters and Beachy Head , the highest chalk sea cliff in Britain at 162 m (531 ft) above sea level. The South Downs may be said to have three main component parts: the East Hampshire Downs, the Western Downs and the Eastern Downs, together with the river valleys that cut across them and the land immediately below them, the scarpfoot . The Western and Eastern Downs are often collectively referred to as

7788-427: The decision to create the South Downs National Park , which came into full operation on 1 April 2011, to protect and restore the Downs. The South Downs have also been designated as a National Character Area (NCA 125) by Natural England . It is bordered by the Hampshire Downs , the Wealden Greensand , the Low Weald and the Pevensey Levels to the north and the South Hampshire Lowlands and South Coast Plain to

7906-421: The dolomitized chalk has been dedolomitized back to calcite. Chalk is highly porous, with typical values of porosity ranging from 35 to 47 per cent. While it is similar in appearance to both gypsum and diatomite , chalk is identifiable by its hardness, fossil content, and its reaction to acid (it produces effervescence on contact). In Western Europe, chalk was formed in the Late Cretaceous Epoch and

8024-463: The earliest crown group birds. Acanthomorph fish, the most diverse group of modern vertebrates, appeared in aquatic habitats around the middle of the Cretaceous. During the Early Cretaceous, flowering plants appeared and began to rapidly diversify, becoming the dominant group of plants across the Earth by the end of the Cretaceous, coincident with the decline and extinction of previously widespread gymnosperm groups. The Cretaceous (along with

8142-437: The early Palaeocene Epoch (between 100 and 61 million years ago). It was deposited on extensive continental shelves at depths between 100 and 600 metres (330 and 1,970 ft), during a time of nonseasonal (likely arid) climate that reduced the amount of erosion from nearby exposed rock. The lack of nearby erosion explains the high purity of chalk. The coccolithophores, foraminifera, and other microscopic organisms from which

8260-544: The early and mid-Cretaceous (becoming extinct during the late Cretaceous Cenomanian-Turonian anoxic event ), plesiosaurs throughout the entire period, and mosasaurs appearing in the Late Cretaceous. Sea turtles in the form of Cheloniidae and Panchelonioidea lived during the period and survived the extinction event. Panchelonioidea is today represented by a single species; the leatherback sea turtle . The Hesperornithiformes were flightless, marine diving birds that swam like grebes . Baculites , an ammonite genus with

8378-437: The east, then receded late in the period, leaving thick marine deposits sandwiched between coal beds. Bivalve palaeobiogeography also indicates that Africa was split in half by a shallow sea during the Coniacian and Santonian, connecting the Tethys with the South Atlantic by way of the central Sahara and Central Africa, which were then underwater. Yet another shallow seaway ran between what is now Norway and Greenland, connecting

8496-747: The end of the AACS, which ended around 111 Ma with the Paquier/Urbino Thermal Maximum, giving way to the Mid-Cretaceous Hothouse (MKH), which lasted from the early Albian until the early Campanian. Faster rates of seafloor spreading and entry of carbon dioxide into the atmosphere are believed to have initiated this period of extreme warmth, along with high flood basalt activity. The MKH was punctuated by multiple thermal maxima of extreme warmth. The Leenhardt Thermal Event (LTE) occurred around 110 Ma, followed shortly by

8614-501: The end of the Cretaceous. The high sea level and warm climate of the Cretaceous meant large areas of the continents were covered by warm, shallow seas, providing habitat for many marine organisms. The Cretaceous was named for the extensive chalk deposits of this age in Europe, but in many parts of the world, the deposits from the Cretaceous are of marine limestone , a rock type that is formed under warm, shallow marine conditions. Due to

8732-463: The end of the period only three highly specialized families remained; Pteranodontidae , Nyctosauridae , and Azhdarchidae . The Liaoning lagerstätte ( Yixian Formation ) in China is an important site, full of preserved remains of numerous types of small dinosaurs, birds and mammals, that provides a glimpse of life in the Early Cretaceous. The coelurosaur dinosaurs found there represent types of

8850-407: The enlarged ridges—enriched the oceans in calcium ; this made the oceans more saturated, as well as increased the bioavailability of the element for calcareous nanoplankton . These widespread carbonates and other sedimentary deposits make the Cretaceous rock record especially fine. Famous formations from North America include the rich marine fossils of Kansas 's Smoky Hill Chalk Member and

8968-550: The enquiry process a number of boundary questions were considered, so that the National Park contains areas not in the former AONBs, and vice versa. The South Downs contain a number of national nature reserves (NNRs). The NNRs on the Sussex Downs comprise Kingley Vale , near Chichester , said by Natural England to contain one of the finest yew forests in Europe, including a grove of ancient trees which are among

9086-528: The extinction fed on insects , larvae , worms , and snails, which in turn fed on dead plant and animal matter. Scientists theorise that these organisms survived the collapse of plant-based food chains because they fed on detritus . In stream communities , few groups of animals became extinct. Stream communities rely less on food from living plants and more on detritus that washes in from land. This particular ecological niche buffered them from extinction. Similar, but more complex patterns have been found in

9204-558: The first records of the gharial-like Neochoristodera , which appear to have evolved in the regional absence of aquatic neosuchian crocodyliformes. During the Late Cretaceous the neochoristodere Champsosaurus was widely distributed across western North America. Due to the extreme climatic warmth in the Arctic, choristoderans were able to colonise it too during the Late Cretaceous. In the seas, rays , modern sharks and teleosts became common. Marine reptiles included ichthyosaurs in

9322-503: The genus Berriasella , but its use as a stratigraphic indicator has been questioned, as its first appearance does not correlate with that of C. alpina . The boundary is officially considered by the International Commission on Stratigraphy to be approximately 145 million years ago, but other estimates have been proposed based on U-Pb geochronology, ranging as young as 140 million years ago. The upper boundary of

9440-625: The group Maniraptora , which includes modern birds and their closest non-avian relatives, such as dromaeosaurs , oviraptorosaurs , therizinosaurs , troodontids along with other avialans . Fossils of these dinosaurs from the Liaoning lagerstätte are notable for the presence of hair-like feathers . Insects diversified during the Cretaceous, and the oldest known ants , termites and some lepidopterans , akin to butterflies and moths , appeared. Aphids , grasshoppers and gall wasps appeared. Rhynchocephalians (which today only includes

9558-412: The high sea level, there was extensive space for such sedimentation . Because of the relatively young age and great thickness of the system, Cretaceous rocks are evident in many areas worldwide. Chalk is a rock type characteristic for (but not restricted to) the Cretaceous. It consists of coccoliths , microscopically small calcite skeletons of coccolithophores , a type of algae that prospered in

9676-551: The highest rates of extinction and turnover. Thylacocephala , a class of crustaceans, went extinct in the Late Cretaceous. The first radiation of the diatoms (generally siliceous shelled, rather than calcareous ) in the oceans occurred during the Cretaceous; freshwater diatoms did not appear until the Miocene . Calcareous nannoplankton were important components of the marine microbiota and important as biostratigraphic markers and recorders of environmental change. The Cretaceous

9794-588: The idea received firm government support. After a public enquiry that took place between 2003 and 2009, the government announced its decision to make the South Downs a national park on 31 March 2009. The South Downs National Park finally came into operation on 1 April 2011. Within its boundary are included not only the South Downs proper but also part of the western Weald , a geologically and ecologically quite different district. The South Downs National Park has replaced two Areas of Outstanding Natural Beauty (AONB)s : East Hampshire AONB and Sussex Downs AONB . During

9912-767: The last epoch of the Jurassic, the Tithonian, continued into the Berriasian, the first age of the Cretaceous. The North Atlantic seaway opened and enabled the flow of cool water from the Boreal Ocean into the Tethys. There is evidence that snowfalls were common in the higher latitudes during this age, and the tropics became wetter than during the Triassic and Jurassic. Glaciation was restricted to high- latitude mountains, though seasonal snow may have existed farther from

10030-575: The late Valanginian (~ 134 million years ago) found in Israel and Italy, initially at low abundance. Molecular clock estimates conflict with fossil estimates, suggesting the diversification of crown-group angiosperms during the Late Triassic or the Jurassic, but such estimates are difficult to reconcile with the heavily sampled pollen record and the distinctive tricolpate to tricolporoidate (triple grooved) pollen of eudicot angiosperms. Among

10148-465: The late Cretaceous, and all else that depended on them suffered, as well. Herbivorous animals, which depended on plants and plankton as their food, died out as their food sources became scarce; consequently, the top predators , such as Tyrannosaurus rex , also perished. Yet only three major groups of tetrapods disappeared completely; the nonavian dinosaurs , the plesiosaurs and the pterosaurs . The other Cretaceous groups that did not survive into

10266-574: The latest Albian. Approximately 94 Ma, the Cenomanian-Turonian Thermal Maximum occurred, with this hyperthermal being the most extreme hothouse interval of the Cretaceous and being associated with a sea level highstand. Temperatures cooled down slightly over the next few million years, but then another thermal maximum, the Coniacian Thermal Maximum, happened, with this thermal event being dated to around 87 Ma. Atmospheric CO 2 levels may have varied by thousands of ppm throughout

10384-598: The low-lying clay vales of the Low Weald, formed of less resistant Weald Clay , and finally the more highly resistant sandstones of the High Weald at the centre of the anticline, whose elevated forest ridge includes most notably Ashdown Forest . The chalk, being porous, allows water to soak through; as a result there are many winterbournes along the northern edge. The South Downs are a long chalk escarpment that stretches for over 110 km (68 mi), rising from

10502-711: The l’Arboudeyesse Thermal Event (ATE) a million years later. Following these two hyperthermals was the Amadeus Thermal Maximum around 106 Ma, during the middle Albian. Then, around a million years after that, occurred the Petite Verol Thermal Event (PVTE). Afterwards, around 102.5 Ma, the Event 6 Thermal Event (EV6) took place; this event was itself followed by the Breistroffer Thermal Maximum around 101 Ma, during

10620-517: The middle Cretaceous, becoming the dominant group of land plants by the end of the period, coincident with the decline of previously dominant groups such as conifers. The oldest known fossils of grasses are from the Albian , with the family having diversified into modern groups by the end of the Cretaceous. The oldest large angiosperm trees are known from the Turonian (c. 90 Mya) of New Jersey, with

10738-473: The middle of the 20th century, an agricultural system operated by downland farmers known as 'sheep-and-corn farming' underpinned this: the sheep (most famously the Southdown breed) of villagers would be systematically confined to certain corn fields to improve their fertility with their droppings and then they would be let out onto the downland to graze. However, starting in 1940 with government measures during

10856-528: The mineral gypsum ( calcium sulfate ). While gypsum-based blackboard chalk is the lowest cost to produce, and thus widely used in the developing world , use of carbonate-based chalk produces larger particles and thus less dust, and it is marketed as "dustless chalk". Coloured chalks, pastel chalks, and sidewalk chalk (shaped into larger sticks and often coloured), used to draw on sidewalks , streets, and driveways , are primarily made of gypsum rather than calcium carbonate chalk. Magnesium carbonate chalk

10974-562: The most famous is the extensive complex at Grimes Graves in Norfolk . Chalk was traditionally used in recreation. In field sports, such as tennis played on grass, powdered chalk was used to mark the boundary lines of the playing field or court. If a ball hits the line, a cloud of chalk or pigment dust will be visible. In recent years, powdered chalk has been replaced with titanium dioxide . In gymnastics, rock-climbing, weightlifting and tug of war , chalk — now usually magnesium carbonate —

11092-470: The most promising candidates for fixing the Jurassic–Cretaceous boundary. In particular, the first appearance Calpionella alpina , coinciding with the base of the eponymous Alpina subzone, has been proposed as the definition of the base of the Cretaceous. The working definition for the boundary has often been placed as the first appearance of the ammonite Strambergella jacobi , formerly placed in

11210-611: The northern fringe of Friston Forest north-west of Eastbourne, one of the largest areas of chalk heath in Britain. The NNRs on the East Hampshire Downs comprise Butser Hill , near Petersfield, a large area of chalk grassland on the highest point in the South Downs (a large area is also designated as a scheduled monument reflecting its historical significance, particularly in the Bronze and Iron Ages); Old Winchester Hill ,

11328-824: The oceans. Extinction was more severe among animals living in the water column than among animals living on or in the seafloor. Animals in the water column are almost entirely dependent on primary production from living phytoplankton, while animals living on or in the ocean floor feed on detritus or can switch to detritus feeding. The largest air-breathing survivors of the event, crocodilians and champsosaurs , were semiaquatic and had access to detritus. Modern crocodilians can live as scavengers and can survive for months without food and go into hibernation when conditions are unfavorable, and their young are small, grow slowly, and feed largely on invertebrates and dead organisms or fragments of organisms for their first few years. These characteristics have been linked to crocodilian survival at

11446-406: The oldest living things in Britain (the reserve is also one of the most important archaeological sites in southern England, with 14 scheduled monuments ); Castle Hill , between Brighton and Lewes, an important example of ancient, traditionally managed grassland; Lewes Downs ( Mount Caburn ), a traditionally managed chalk downland (and also an important archaeological site); and Lullington Heath , on

11564-601: The oldest records of Angiosperm macrofossils are Montsechia from the Barremian aged Las Hoyas beds of Spain and Archaefructus from the Barremian-Aptian boundary Yixian Formation in China. Tricolpate pollen distinctive of eudicots first appears in the Late Barremian, while the earliest remains of monocots are known from the Aptian. Flowering plants underwent a rapid radiation beginning during

11682-523: The poles. After the end of the first age, however, temperatures began to increase again, with a number of thermal excursions, such as the middle Valanginian Weissert Thermal Excursion (WTX), which was caused by the Paraná-Etendeka Large Igneous Province's activity. It was followed by the middle Hauterivian Faraoni Thermal Excursion (FTX) and the early Barremian Hauptblatterton Thermal Event (HTE). The HTE marked

11800-412: The principal food of mosasaurs , a group of giant marine lizards related to snakes that became extinct at the boundary. Omnivores , insectivores , and carrion -eaters survived the extinction event, perhaps because of the increased availability of their food sources. At the end of the Cretaceous, there seem to have been no purely herbivorous or carnivorous mammals . Mammals and birds that survived

11918-547: The punctuation mark at the end of a progressive decline in biodiversity during the Maastrichtian age. The result was the extinction of three-quarters of Earth's plant and animal species. The impact created the sharp break known as the K–Pg boundary (formerly known as the K–T boundary). Earth's biodiversity required substantial time to recover from this event, despite the probable existence of an abundance of vacant ecological niches . Despite

12036-744: The rise of angiosperms, during the Jurassic and the Early Cretaceous, the higher flora was dominated by gymnosperm groups, including cycads , conifers , ginkgophytes , gnetophytes and close relatives, as well as the extinct Bennettitales . Other groups of plants included pteridosperms or "seed ferns", a collective term that refers to disparate groups of extinct seed plants with fern-like foliage, including groups such as Corystospermaceae and Caytoniales . The exact origins of angiosperms are uncertain, although molecular evidence suggests that they are not closely related to any living group of gymnosperms. The earliest widely accepted evidence of flowering plants are monosulcate (single-grooved) pollen grains from

12154-562: The sea in places such as the Dover cliffs on the Kent coast of the English Channel . Chalk is mined for use in industry, such as for quicklime , bricks and builder's putty , and in agriculture , for raising pH in soils with high acidity . It is also used for " blackboard chalk " for writing and drawing on various types of surfaces, although these can also be manufactured from other carbonate-based minerals, or gypsum . Chalk

12272-495: The sense of 'elevated rolling grassland' around the 14th century. These hills are prefixed 'south' to distinguish them from another chalk escarpment , the North Downs , which runs roughly parallel to them about 30 mi (48 km) away on the northern edge of the Weald. The South Downs are formed from a thick band of chalk which was deposited during the Cretaceous Period between 100 and 66 million years ago within

12390-451: The severity of the K-Pg extinction event, there were significant variations in the rate of extinction between and within different clades . Species that depended on photosynthesis declined or became extinct as atmospheric particles blocked solar energy . As is the case today, photosynthesizing organisms, such as phytoplankton and land plants , formed the primary part of the food chain in

12508-436: The small particles of chalk make it a substance ideal for cleaning and polishing. For example, toothpaste commonly contains small amounts of chalk, which serves as a mild abrasive . Polishing chalk is chalk prepared with a carefully controlled grain size, for very fine polishing of metals. French chalk (also known as tailor's chalk) is traditionally a hard chalk used to make temporary markings on cloth, mainly by tailors . It

12626-425: The south. The downland is a highly popular recreational destination, particularly for walkers, horseriders and mountain bikers. A long distance footpath and bridleway , the South Downs Way , follows the entire length of the chalk ridge from Winchester to Eastbourne, complemented by many interconnecting public footpaths and bridleways. The term 'downs' is from Old English dūn , meaning 'hill'. The word acquired

12744-422: The strong regionality of most biostratigraphic markers, and the lack of any chemostratigraphic events, such as isotope excursions (large sudden changes in ratios of isotopes ) that could be used to define or correlate a boundary. Calpionellids , an enigmatic group of planktonic protists with urn-shaped calcitic tests briefly abundant during the latest Jurassic to earliest Cretaceous, have been suggested as

12862-582: The terrestrial fauna of the late Cretaceous Hell Creek Formation . Other important Cretaceous exposures occur in Europe (e.g., the Weald ) and China (the Yixian Formation ). In the area that is now India, massive lava beds called the Deccan Traps were erupted in the very late Cretaceous and early Paleocene. Palynological evidence indicates the Cretaceous climate had three broad phases:

12980-483: The trunk having a preserved diameter of 1.8 metres (5.9 ft) and an estimated height of 50 metres (160 ft). During the Cretaceous, ferns in the order Polypodiales , which make up 80% of living fern species, would also begin to diversify. On land, mammals were generally small sized, but a very relevant component of the fauna , with cimolodont multituberculates outnumbering dinosaurs in some sites. Neither true marsupials nor placentals existed until

13098-789: The ultimate end of the Tithonian-early Barremian Cool Interval (TEBCI). During this interval, precession was the dominant orbital driver of environmental changes in the Vocontian Basin. For much of the TEBCI, northern Gondwana experienced a monsoonal climate. A shallow thermocline existed in the mid-latitude Tethys. The TEBCI was followed by the Barremian-Aptian Warm Interval (BAWI). This hot climatic interval coincides with Manihiki and Ontong Java Plateau volcanism and with

13216-643: The upper Cretaceous of Western Europe . The name Cretaceous was derived from the Latin creta , meaning chalk . The twofold division of the Cretaceous was implemented by Conybeare and Phillips in 1822. Alcide d'Orbigny in 1840 divided the French Cretaceous into five étages (stages): the Neocomian , Aptian, Albian, Turonian, and Senonian, later adding the Urgonian between Neocomian and Aptian and

13334-524: The valley of the River Itchen near Winchester, Hampshire , in the west to Beachy Head near Eastbourne , East Sussex , in the east. Behind the steep north-facing scarp slope, the gently inclined dip slope of undulating chalk downland extends for a distance of up to 7 mi (11 km) southwards. Viewed from high points further north in the High Weald and on the North Downs, the scarp of

13452-628: The very end, but a variety of non-marsupial metatherians and non-placental eutherians had already begun to diversify greatly, ranging as carnivores ( Deltatheroida ), aquatic foragers ( Stagodontidae ) and herbivores ( Schowalteria , Zhelestidae ). Various "archaic" groups like eutriconodonts were common in the Early Cretaceous, but by the Late Cretaceous northern mammalian faunas were dominated by multituberculates and therians , with dryolestoids dominating South America . The apex predators were archosaurian reptiles , especially dinosaurs , which were at their most diverse stage. Avians such as

13570-746: The village of Slindon (near Arundel) and ends at the Queen Elizabeth Country Park (to the south of Petersfield.) Longer events that take in the South Downs Way include a 100-mile running 'ultramarathon' and mountain biking 75 mile night time race from Beachy Head to Queen Elizabeth Country Park. Three of the landmarks on the Downs are the Long Man of Wilmington and the Litlington White Horse being chalk carved hill figures , and Clayton Windmills . There

13688-407: The world, alternative local subdivisions are still in use. From youngest to oldest, the subdivisions of the Cretaceous period are: The lower boundary of the Cretaceous is currently undefined, and the Jurassic–Cretaceous boundary is currently the only system boundary to lack a defined Global Boundary Stratotype Section and Point (GSSP). Placing a GSSP for this boundary has been difficult because of

13806-654: Was followed by the Aptian-Albian Cold Snap (AACS) that began about 118 Ma. A short, relatively minor ice age may have occurred during this so-called "cold snap", as evidenced by glacial dropstones in the western parts of the Tethys Ocean and the expansion of calcareous nannofossils that dwelt in cold water into lower latitudes. The AACS is associated with an arid period in the Iberian Peninsula . Temperatures increased drastically after

13924-454: Was largely ice-free, although there is some evidence of brief periods of glaciation during the cooler first half, and forests extended to the poles. Many of the dominant taxonomic groups present in modern times can be ultimately traced back to origins in the Cretaceous. During this time, new groups of mammals and birds appeared, including the earliest relatives of placentals & marsupials ( Eutheria and Metatheria respectively), and

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