The Cretaceous is a geologic period and system that spans 79 million years from the end of the Jurassic Period 145 million years ago to the beginning of the Paleogene Period 66 mya. It is the last period of the Mesozoic Era, the longest period of the Phanerozoic Eon; the Cretaceous Period is abbreviated K, for its German translation Kreide. The Cretaceous was a period with a 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 and rudists, while dinosaurs continued to dominate on land. During this time, new groups of mammals and birds, as well as flowering plants, appeared; the Cretaceous ended with the Cretaceous–Paleogene extinction event, a large mass extinction in which many groups, including non-avian dinosaurs and large marine reptiles died out. The end of the Cretaceous is defined by the abrupt Cretaceous–Paleogene boundary, a geologic signature associated with the mass extinction which 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, using strata in the Paris Basin and named for the extensive beds of chalk, found in the upper Cretaceous of Western Europe. The name Cretaceous was derived from Latin creta; 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 and Senonian. A subdivision in eleven stages, all originating from European stratigraphy, is now used worldwide. In many parts of the world, alternative local subdivisions are still in use; as with other older geologic periods, the rock beds of the Cretaceous are well identified but the exact age of the system's base is uncertain by a few million years. No great extinction or burst of diversity separates the Cretaceous from the Jurassic. However, the top of the system is defined, being placed at an iridium-rich layer found worldwide, believed to be associated with the Chicxulub impact crater, with its boundaries circumscribing parts of the Yucatán Peninsula and into the Gulf of Mexico.
This layer has been dated at 66.043 Ma. A 140 Ma age for the Jurassic-Cretaceous boundary instead of the accepted 145 Ma was proposed in 2014 based on a stratigraphic study of Vaca Muerta Formation in Neuquén Basin, Argentina. Víctor Ramos, one of the authors of the study proposing the 140 Ma boundary age sees the study as a "first step" toward formally changing the age in the International Union of Geological Sciences. From youngest to oldest, the subdivisions of the Cretaceous period are: Late Cretaceous Maastrichtian – Campanian – Santonian – Coniacian – Turonian – Cenomanian – Early Cretaceous Albian – Aptian – Barremian – Hauterivian – Valanginian – Berriasian – 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, formed under warm, shallow marine circumstances.
Due to the high sea level, there was extensive space for such sedimentation. Because of the young age and great thickness of the system, Cretaceous rocks are evident in many areas worldwide. Chalk is a rock type characteristic for the Cretaceous, it consists of coccoliths, microscopically small calcite skeletons of coccolithophores, a type of algae that prospered in the Cretaceous seas. 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 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 consolidated and the Chalk Group still consists of loose sediments in many places; the group has other limestones and arenites. Among the fossils it contains are sea urchins, belemnites and sea reptiles such as Mosasaurus. In southern Europe, the Cretaceous is 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. Stagnation of deep sea currents in middle Cretaceous times caused anoxic conditions in the sea water leaving the deposited organic matter undecomposed. Half the worlds 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; these shales are an important source rock for oil and gas, for example in the subsurface of the North Sea. During th
East Sussex is a county in South East England. It is bordered by the counties of Kent to the north and east, Surrey to the north west and West Sussex to the west, to the south by the English Channel. East Sussex is part of the historic county of Sussex, which has its roots in the ancient kingdom of the South Saxons, who established themselves there in the 5th century AD, after the departure of the Romans. Archaeological remains are plentiful in the upland areas; the area's position on the coast has meant that there were many invaders, including the Romans and the Normans. Earlier industries have included fishing, iron-making, the wool trade, all of which have declined, or been lost completely. Sussex is traditionally sub-divided into six rapes. From the 12th century the three eastern rapes together and the three western rapes together had separate quarter sessions, with the county town of the three eastern rapes being Lewes; this situation was formalised by Parliament in 1865, the two parts were made into administrative counties, each with distinct elected county councils in 1889 under the Local Government Act 1888.
In East Sussex there were three self-administered county boroughs: Brighton and Hastings. In 1974 East Sussex was made a non-metropolitan and ceremonial county, the three county boroughs became districts within the county. At the same time the western boundary was altered, so that the Mid Sussex region was transferred to the county of West Sussex. In 1997, Brighton and Hove became a self-administered unitary authority. East Sussex is divided into five local government districts. Three are larger, districts: Lewes. Eastbourne and Hastings are urban areas; the rural districts are further subdivided into civil parishes. From a geological point of view East Sussex is part of southern anticline of the Weald: the South Downs, a range of moderate chalk hills which run across the southern part of the county from west to east and mirrored in Kent by the North Downs. To the north lie parallel valleys and ridges, the highest of, the Weald itself; the sandstones and clays meet the sea at Hastings. The area contains significant reserves of shale oil, totalling 4.4 billion barrels of oil in the Wealden basin according to a 2014 study, which Business and Energy Minister Michael Fallon said "will bring jobs and business opportunities" and help with UK energy self-sufficiency.
Fracking in the area is required to achieve these objectives, opposed by environmental groups. East Sussex, like most counties by the south coast, has an annual average total of around 1,750 hours of sunshine per year; this is much higher than the UK's average of about 1,340 hours of sunshine a year. The relief of the county reflects the geology; the chalk uplands of the South Downs occupies the coastal strip between Eastbourne. There are two river gaps: Cuckmere; the Seven Sisters, where the Downs meet the sea, are the remnants of dry valleys cut into the chalk. To the east of Beachy Head lie the marshlands of the Pevensey Levels flooded by the sea but now enclosed within a deposited beach. At Bexhill the land begins to rise again where the clays of the Weald meet the sea. Further east are the Pett Levels, more marshland, beyond, the estuary of the River Rother. On the far side of the estuary are the dunes of Camber Sands; the highest point of the Downs within the county is Ditchling Beacon, at 814 feet: it is termed a Marilyn.
The Weald occupies the northern borderlands of the county. Between the Downs and Weald is a narrow stretch of lower lying land; the High Weald is wooded in contrast to the South Downs. Part of the Weald is the Ashdown Forest; the location of settlements in East Sussex has been determined both by its history and its geography. The original towns and villages tended to be where its economy lay: fishing along the coast and agriculture and iron mining on the Weald. Industry today tends to be geared towards tourism, along the coastal strip. Here towns such as Bexhill-on-Sea and Hastings lie. Newhaven and Rye are ports, although the latter is of historical importance. Peacehaven and Seaford are more dormitory towns than anything else. Away from the coast lie former market towns such as Hailsham and Uckfield. Lewes, the County town of East Sussex; this is a chart of trend of regional gross value added of the non-metropolitan county of East Sussex at current basic prices published by Office for National Statistics with figures in millions of British Pounds Sterling.
The Seven Sisters Park is part of the South Downs National Park. Beachy Head is one of the most famed local attractions, along with the flats along Normans Bay. Apart from the physical landmarks such as the Downs and the Weald, East Sussex has a great many landmarks of historical interest. There are castles at Bodiam, Herstmonceux and Pevensey. Battle Abbey, built to commemorate the Battle of Hastings.
Kent is a county in South East England and one of the home counties. It borders Surrey to the west and East Sussex to the south-west; the county shares borders with Essex along the estuary of the River Thames, with the French department of Pas-de-Calais through the Channel Tunnel. The county town is Maidstone. Canterbury Cathedral in Kent has been the seat of the Archbishop of Canterbury, leader of the Church of England, since the Reformation. Prior to that it was built by Catholics, dating back to the conversion of England to Catholicism by Saint Augustine that began in the 6th century. Before the English Reformation the cathedral was part of a Benedictine monastic community known as Christ Church, Canterbury, as well as being the seat of the Catholic Archbishop of Canterbury; the last Catholic Archbishop of Canterbury was Reginald Pole. Rochester Cathedral is in Kent, in Medway, it is the second-oldest cathedral in England, with Canterbury Cathedral being the oldest. Between London and the Strait of Dover, which separates it from mainland Europe, Kent has seen both diplomacy and conflict, ranging from the Leeds Castle peace talks of 1978 and 2004 to the Battle of Britain in World War II.
England relied on the county's ports to provide warships through much of its history. France can be seen in fine weather from Folkestone and the White Cliffs of Dover. Hills in the form of the North Downs and the Greensand Ridge span the length of the county and in the series of valleys in between and to the south are most of the county's 26 castles; because of its relative abundance of fruit-growing and hop gardens, Kent is known as "The Garden of England". Kent's economy is diversified. In northwest Kent industries include extraction of aggregate building materials and scientific research. Coal mining has played its part in Kent's industrial heritage. Large parts of Kent are within the London commuter belt and its strong transport connections to the capital and the nearby continent makes Kent a high-income county. Twenty-eight per cent of the county forms part of two Areas of Outstanding Natural Beauty: the North Downs and The High Weald; the name Kent is believed to be of British Celtic origin and was known in Old English as Cent, Cent lond, Centrice.
In Latin sources Kent is mentioned as Canticum. The meaning is explained by some researchers as "coastal district," or "corner-land, land on the edge". If so, the name could be etymologically related to the placename Cantabria a Celtiberian-speaking coastal region in pre-Roman Iberia, today a province of Spain; the area has been occupied since the Palaeolithic era, as attested by finds from the quarries at Swanscombe. The Medway megaliths were built during the Neolithic era. There is a rich sequence of Bronze Age, Iron Age, Roman era occupation, as indicated by finds and features such as the Ringlemere gold cup and the Roman villas of the Darent valley; the modern name of Kent is derived from the Brythonic word kantos meaning "rim" or "border", or from a homonymous word kanto "horn, hook". This describes the eastern part of the current county area as coastal district. Julius Caesar had described the area as um, or home of the Cantiaci in 51 BC; the extreme west of the modern county was by the time of Roman Britain occupied by Iron Age tribes, known as the Regnenses.
Caesar wrote that the people of Kent are'by far the most civilised inhabitants of Britain'. East Kent became a kingdom of the Jutes during the 5th century and was known as Cantia from about 730 and recorded as Cent in 835; the early medieval inhabitants of the county were known as the Kent people. These people regarded the city of Canterbury as their capital. In 597, Pope Gregory I appointed the religious missionary as the first Archbishop of Canterbury. In the previous year, Augustine converted the pagan King Æthelberht of Kent to Christianity; the Diocese of Canterbury became England's first Episcopal See with first cathedral and has since remained England's centre of Christianity. The second designated English cathedral was in Kent at Rochester Cathedral. In the 11th century, the people of Kent adopted the motto Invicta, meaning "undefeated" or "unconquered"; this naming followed the invasion of Britain by William of Normandy. The Kent people's continued resistance against the Normans led to Kent's designation as a semi-autonomous county palatine in 1067.
Under the nominal rule of William's half-brother Odo of Bayeux, the county was granted similar powers to those granted in the areas bordering Wales and Scotland. Kent was traditionally partitioned into East and West Kent, into lathes and hundreds; the traditional border of East and West Kent was the Medway. Men and women from east of the Medway are Men of Kent, those from the west are Kentishmen or Kentish Maids. During the medieval and early modern period, Kent played a major role in several of England's most notable rebellions, including the Peasants' Revolt of 1381, led by Wat Tyler,Jack Cade's Kent rebellion of 1450, Wyatt's Rebellion of 1554 against Queen Mary I; the Royal Navy first used the River Medway in 1547. By the reign of Elizabeth I a small dockyard had been established at Chatham. By 1618, storehouses, a ropewalk, a drydock, houses for officials had
Selenite known as satin spar, desert rose, or gypsum flower are four crystal structure varieties of the mineral gypsum. These four varieties of gypsum may be called selenite. All varieties of gypsum, including selenite and alabaster, are composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. Selenite contains no significant selenium, the similarity of the names of the substances coming from the Ancient Greek word for the Moon; some of the largest crystals found are of selenite, the largest specimen found in the Naica Mine's Cave of the Crystals being 12 metres long and weighing 55 tons. The etymology of selenite is through Middle English selenite, from Latin selenites, from Greek selēnitēs moonstone or stone of the moon, from selēnē; the ancients had a belief that certain transparent crystals waned with the moon. From the 15th century, "selenite" has referred to the variety of gypsum that occurs in transparent crystals or crystalline masses. All varieties of gypsum are soft minerals.
This is the most important identifying characteristic of gypsum, as any variety of gypsum can be scratched with a fingernail. Because gypsum has natural thermal insulating properties, all varieties feel warm to the touch. Though sometimes grouped together as "selenite", the four crystalline varieties have differences. General identifying descriptions of the related crystalline varieties are: most transparent and colorless: it is named after Greek σεληνη "the moon". If selenite crystals show translucency, and/or color, it is caused by the presence of other minerals, sometimes in druse druse is the crust of tiny, minute, or micro crystals that form or fuse either within or upon the surface of a rock vug, geode, or another crystal most silky and translucent. Rosette shaped gypsum with outer druse of sand or with sand throughout – most sand colored the desert rose name can be applied to barite desert roses – barite is a harder mineral with higher density rosette shaped gypsum with spreading fibers – can include outer druse the difference between desert roses and gypsum flowers is that desert roses look like roses, whereas gypsum flowers form a myriad of shapes Varieties of gypsum known as "satin spar" and "alabaster" are used for a variety of ornamental purposes like sculptures and a substitute for window glass.
But because of the long history of the commercial value and use of both gypsum and alabaster, the four crystalline varieties have been somewhat ignored, except as a curiosity or as rock collectibles. Crystal habit refers to the shapes. Selenite crystals occur as tabular and columnar crystals with no imperfections or inclusions, thereby can appear water or glass-like. Many collectible selenite crystals have interesting inclusions such as, accompanying related minerals, interior druse and fossils. In some rare instances, water was encased as a fluid inclusion. Selenite crystals sometimes form in thin tabular or mica-like sheets and have been used as glass panes as at Santa Sabina in Rome. Selenite crystals sometimes will exhibit bladed rosette habit with accompanying transparent, columnar crystals. Selenite crystals can be found both attached to a matrix or base rock, but can be found as entire free-floating crystals in clay beds. Satin spar is always prismatic and fibrous in a parallel crystal habit.
Satin spar occurs in seams, some of them quite long, is attached to a matrix or base rock. Desert roses are most bladed, exhibiting the familiar shape of a rose, always have an exterior druse. Desert roses are always unattached to a matrix or base rock. Gypsum flowers are most acicular, scaly and lenticular. Gypsum flowers most exhibit simple twinning. Selenite crystals can exhibit “arrow/spear-head” as well as “duck-bill” twins. Both selenite crystals and gypsum flowers sometimes form quite densely in acicular nets. Gypsum flowers are attached to a matrix or base rock. Gypsum crystals are colorless, gray, beige, pink, light red, green. Colors are caused by the presence of other mineral inclusions such as, copper ores and sulfides, iron ores, calcite and opal. Gypsum crystals can be transparent and opaque. Opacity can be caused by impurities, inclusions and crust, can occur in all four crystalline varieties. Both selenite and satin spar are glassy or vitreous and silky – on cleavage surfaces. Luster is not exhibited in the rosettes, due to their exterior druse.
Gypsum flowers exhibit more luster than desert r
Limestone is a carbonate sedimentary rock, composed of the skeletal fragments of marine organisms such as coral and molluscs. Its major materials are the minerals calcite and aragonite, which are different crystal forms of calcium carbonate. A related rock is dolostone, which contains a high percentage of the mineral dolomite, CaMg2. In fact, in old USGS publications, dolostone was referred to as magnesian limestone, a term now reserved for magnesium-deficient dolostones or magnesium-rich limestones. About 10% of sedimentary rocks are limestones; the solubility of limestone in water and weak acid solutions leads to karst landscapes, in which water erodes the limestone over thousands to millions of years. Most cave systems are through limestone bedrock. Limestone has numerous uses: as a building material, an essential component of concrete, as aggregate for the base of roads, as white pigment or filler in products such as toothpaste or paints, as a chemical feedstock for the production of lime, as a soil conditioner, or as a popular decorative addition to rock gardens.
Like most other sedimentary rocks, most limestone is composed of grains. Most grains in limestone are skeletal fragments of marine organisms such as foraminifera; these organisms secrete shells made of aragonite or calcite, leave these shells behind when they die. Other carbonate grains composing limestones are ooids, peloids and extraclasts. Limestone contains variable amounts of silica in the form of chert or siliceous skeletal fragment, varying amounts of clay and sand carried in by rivers; some limestones do not consist of grains, are formed by the chemical precipitation of calcite or aragonite, i.e. travertine. Secondary calcite may be deposited by supersaturated meteoric waters; this produces speleothems, such as stalactites. Another form taken by calcite is oolitic limestone, which can be recognized by its granular appearance; the primary source of the calcite in limestone is most marine organisms. Some of these organisms can construct mounds of rock building upon past generations. Below about 3,000 meters, water pressure and temperature conditions cause the dissolution of calcite to increase nonlinearly, so limestone does not form in deeper waters.
Limestones may form in lacustrine and evaporite depositional environments. Calcite can be dissolved or precipitated by groundwater, depending on several factors, including the water temperature, pH, dissolved ion concentrations. Calcite exhibits an unusual characteristic called retrograde solubility, in which it becomes less soluble in water as the temperature increases. Impurities will cause limestones to exhibit different colors with weathered surfaces. Limestone may be crystalline, granular, or massive, depending on the method of formation. Crystals of calcite, dolomite or barite may line small cavities in the rock; when conditions are right for precipitation, calcite forms mineral coatings that cement the existing rock grains together, or it can fill fractures. Travertine is a banded, compact variety of limestone formed along streams where there are waterfalls and around hot or cold springs. Calcium carbonate is deposited where evaporation of the water leaves a solution supersaturated with the chemical constituents of calcite.
Tufa, a porous or cellular variety of travertine, is found near waterfalls. Coquina is a poorly consolidated limestone composed of pieces of coral or shells. During regional metamorphism that occurs during the mountain building process, limestone recrystallizes into marble. Limestone is a parent material of Mollisol soil group. Two major classification schemes, the Folk and the Dunham, are used for identifying the types of carbonate rocks collectively known as limestone. Robert L. Folk developed a classification system that places primary emphasis on the detailed composition of grains and interstitial material in carbonate rocks. Based on composition, there are three main components: allochems and cement; the Folk system uses two-part names. It is helpful to have a petrographic microscope when using the Folk scheme, because it is easier to determine the components present in each sample; the Dunham scheme focuses on depositional textures. Each name is based upon the texture of the grains. Robert J. Dunham published his system for limestone in 1962.
Dunham divides the rocks into four main groups based on relative proportions of coarser clastic particles. Dunham names are for rock families, his efforts deal with the question of whether or not the grains were in mutual contact, therefore self-supporting, or whether the rock is characterized by the presence of frame builders and algal mats. Unlike the Folk scheme, Dunham deals with the original porosity of the rock; the Dunham scheme is more useful for hand samples because it is based on texture, not the grains in the sample. A revised classification was proposed by Wright, it adds some diagenetic patterns and can be summarized as follows: See: Carbonate platform About 10% of all sedimentary rocks are limestones. Limestone is soluble in acid, therefore forms many erosional landforms; these include limestone pavements, pot holes, cenotes and gorges. Such erosion landscapes are known
The Carboniferous is a geologic period and system that spans 60 million years from the end of the Devonian Period 358.9 million years ago, to the beginning of the Permian Period, 298.9 Mya. The name Carboniferous means "coal-bearing" and derives from the Latin words carbō and ferō, was coined by geologists William Conybeare and William Phillips in 1822. Based on a study of the British rock succession, it was the first of the modern'system' names to be employed, reflects the fact that many coal beds were formed globally during that time; the Carboniferous is treated in North America as two geological periods, the earlier Mississippian and the Pennsylvanian. Terrestrial animal life was well established by the Carboniferous period. Amphibians were the dominant land vertebrates, of which one branch would evolve into amniotes, the first terrestrial vertebrates. Arthropods were very common, many were much larger than those of today. Vast swaths of forest covered the land, which would be laid down and become the coal beds characteristic of the Carboniferous stratigraphy evident today.
The atmospheric content of oxygen reached its highest levels in geological history during the period, 35% compared with 21% today, allowing terrestrial invertebrates to evolve to great size. The half of the period experienced glaciations, low sea level, mountain building as the continents collided to form Pangaea. A minor marine and terrestrial extinction event, the Carboniferous rainforest collapse, occurred at the end of the period, caused by climate change. In the United States the Carboniferous is broken into Mississippian and Pennsylvanian subperiods; the Mississippian is about twice as long as the Pennsylvanian, but due to the large thickness of coal-bearing deposits with Pennsylvanian ages in Europe and North America, the two subperiods were long thought to have been more or less equal in duration. In Europe the Lower Carboniferous sub-system is known as the Dinantian, comprising the Tournaisian and Visean Series, dated at 362.5-332.9 Ma, the Upper Carboniferous sub-system is known as the Silesian, comprising the Namurian and Stephanian Series, dated at 332.9-298.9 Ma.
The Silesian is contemporaneous with the late Mississippian Serpukhovian plus the Pennsylvanian. In Britain the Dinantian is traditionally known as the Carboniferous Limestone, the Namurian as the Millstone Grit, the Westphalian as the Coal Measures and Pennant Sandstone; the International Commission on Stratigraphy faunal stages from youngest to oldest, together with some of their regional subdivisions, are: A global drop in sea level at the end of the Devonian reversed early in the Carboniferous. There was a drop in south polar temperatures; these conditions had little effect in the deep tropics, where lush swamps to become coal, flourished to within 30 degrees of the northernmost glaciers. Mid-Carboniferous, a drop in sea level precipitated a major marine extinction, one that hit crinoids and ammonites hard; this sea level drop and the associated unconformity in North America separate the Mississippian subperiod from the Pennsylvanian subperiod. This happened about 323 million years ago, at the onset of the Permo-Carboniferous Glaciation.
The Carboniferous was a time of active mountain-building as the supercontinent Pangaea came together. The southern continents remained tied together in the supercontinent Gondwana, which collided with North America–Europe along the present line of eastern North America; this continental collision resulted in the Hercynian orogeny in Europe, the Alleghenian orogeny in North America. In the same time frame, much of present eastern Eurasian plate welded itself to Europe along the line of the Ural Mountains. Most of the Mesozoic supercontinent of Pangea was now assembled, although North China, South China continents were still separated from Laurasia; the Late Carboniferous Pangaea was shaped like an "O." There were two major oceans in the Carboniferous—Panthalassa and Paleo-Tethys, inside the "O" in the Carboniferous Pangaea. Other minor oceans were shrinking and closed - Rheic Ocean, the small, shallow Ural Ocean and Proto-Tethys Ocean. Average global temperatures in the Early Carboniferous Period were high: 20 °C.
However, cooling during the Middle Carboniferous reduced average global temperatures to about 12 °C. Lack of growth rings of fossilized trees suggest a lack of seasons of a tropical climate. Glaciations in Gondwana, triggered by Gondwana's southward movement, continued into the Permian and because of the lack of clear markers and breaks, the deposits of this glacial period are referred to as Permo-Carboniferous in age; the cooling and drying of the climate led to the Carboniferous Rainforest Collapse during the late Carboniferous. Tropical rainforests fragmented and were devastated by climate change. Carboniferous rocks in Europe and eastern North America consist of a repeated sequence of limestone, sandstone and coal beds. In North America, the early Carboniferous is marine