The Eemian was the interglacial period which began about 130,000 years ago at the end of the Penultimate Glacial Period and ended about 115,000 years ago at the beginning of the Last Glacial Period. It corresponds to Marine Isotope Stage 5e. Although sometimes referred to as the "last interglacial", it was the second-to-latest interglacial period of the current Ice Age, the most recent being the Holocene which extends to the present day; the prevailing Eemian climate was, on average, around 1 to 2 degrees Celsius warmer than that of the Holocene. However, due to global warming, the past few July global temperatures surpassed the July temperatures of the Eemian period. During the Eemian, the proportion of CO2 in the atmosphere was about 280 parts per million; the Eemian is known as the Ipswichian in the UK, the Mikulin interglacial in Russia, the Valdivia interglacial in Chile and the Riss-Würm interglacial in the Alps. Depending on how a specific publication defines the Sangamonian Stage of North America, the Eemian is equivalent to either all or part of it.
The Eemian climate is believed to have been about as stable as that of the Holocene. Changes in the Earth's orbital parameters from today, known as Milankovitch cycles led to greater seasonal temperature variations in the Northern Hemisphere. Although global annual mean temperatures were several degrees warmer than today, during summer months, temperatures in the Arctic region were about 2-4 °C higher than today; the warmest peak of the Eemian was around 125,000 years ago, when forests reached as far north as North Cape, Norway well above the Arctic Circle at 71°10′21″N 25°47′40″E. Hardwood trees such as hazel and oak grew as far north as Finland. At the peak of the Eemian, the Northern Hemisphere winters were warmer and wetter than now, though some areas were slightly cooler than today; the hippopotamus was distributed as far north as the rivers Thames. Trees grew as far north as southern Baffin Island in the Canadian Arctic Archipelago: the northern limit is further south at Kuujjuaq in northern Quebec.
Coastal Alaska was warm enough during the summer due to reduced sea ice in the Arctic Ocean to allow Saint Lawrence Island to have boreal forest, although inadequate precipitation caused a reduction in the forest cover in interior Alaska and Yukon Territory despite warmer conditions. The prairie-forest boundary in the Great Plains of the United States lay further west near Lubbock, whereas the current boundary is near Dallas; the period closed as temperatures fell to conditions cooler and drier than the present, with a 468-year-long aridity pulse in central Europe 116,000 BC, by 112,000 BC, a glacial period had returned. Kaspar et al. performed a comparison of a coupled general circulation model with reconstructed Eemian temperatures for Europe. Central Europe was found to be 1–2 °C warmer than present; the model reproduces these observations, leading them to conclude that these factors are enough to explain the Eemian temperatures. A 2018 study based on soil samples from Sokli in northern Finland identified abrupt cold spells ca. 120,000 years ago caused by shifts in the North Atlantic Current, lasting hundreds of years and causing temperature drops of a few degrees and vegetation changes in these regions.
Sea level at peak was 6 to 9 metres higher than today, with Greenland contributing 0.6 to 3.5 m, thermal expansion and mountain glaciers contributing up to 1 m, an uncertain contribution from Antarctica. Recent research on marine sediment cores offshore of the West Antarctic Ice Sheet suggest that the sheet melted during the Eemian, that ocean waters rose as fast as 2.5 meters per century. Global mean sea surface temperatures are thought to have been higher than in the Holocene, but not by enough to explain the rise in sea level through thermal expansion alone, so melting of polar ice caps must have occurred; because of the sea level drop since the Eemian, exposed fossil coral reefs are common in the tropics in the Caribbean and along the Red Sea coastlines. These reefs contain internal erosion surfaces showing significant sea level instability during the Eemian. A 2007 study found evidence that the Greenland ice core site Dye 3 was glaciated during the Eemian, which implies that Greenland could have contributed at most 2 m to sea level rise.
Scandinavia was an island due to the inundation of vast areas of northern Europe and the West Siberian Plain. The Eemian Stage was first recognized from boreholes in the area of the city of Amersfoort, Netherlands, by Harting, he named the beds "Système Eémien", after the river Eem. Harting noticed the marine molluscan assemblages to be different from the modern fauna of the North Sea. Many species from the Eemian layers nowadays show a much more southern distribution, ranging from South of the Strait of Dover to Portugal and into the Mediterranean. More information on the molluscan assemblages is given by Lorié, Spaink. Since their discovery, Eemian beds in the Netherlands have been recognized by their marine molluscan content combined with
The Devonian is a geologic period and system of the Paleozoic, spanning 60 million years from the end of the Silurian, 419.2 million years ago, to the beginning of the Carboniferous, 358.9 Mya. It is named after Devon, where rocks from this period were first studied; the first significant adaptive radiation of life on dry land occurred during the Devonian. Free-sporing vascular plants began to spread across dry land, forming extensive forests which covered the continents. By the middle of the Devonian, several groups of plants had evolved leaves and true roots, by the end of the period the first seed-bearing plants appeared. Various terrestrial arthropods became well-established. Fish reached substantial diversity during this time, leading the Devonian to be dubbed the "Age of Fishes." The first ray-finned and lobe-finned bony fish appeared, while the placoderms began dominating every known aquatic environment. The ancestors of all four-limbed vertebrates began adapting to walking on land, as their strong pectoral and pelvic fins evolved into legs.
In the oceans, primitive sharks became more numerous than in the Late Ordovician. The first ammonites, species of molluscs, appeared. Trilobites, the mollusc-like brachiopods and the great coral reefs, were still common; the Late Devonian extinction which started about 375 million years ago affected marine life, killing off all placodermi, all trilobites, save for a few species of the order Proetida. The palaeogeography was dominated by the supercontinent of Gondwana to the south, the continent of Siberia to the north, the early formation of the small continent of Euramerica in between; the period is named after Devon, a county in southwestern England, where a controversial argument in the 1830s over the age and structure of the rocks found distributed throughout the county was resolved by the definition of the Devonian period in the geological timescale. The Great Devonian Controversy was a long period of vigorous argument and counter-argument between the main protagonists of Roderick Murchison with Adam Sedgwick against Henry De la Beche supported by George Bellas Greenough.
Murchison and Sedgwick named the period they proposed as the Devonian System. While the rock beds that define the start and end of the Devonian period are well identified, the exact dates are uncertain. According to the International Commission on Stratigraphy, the Devonian extends from the end of the Silurian 419.2 Mya, to the beginning of the Carboniferous 358.9 Mya. In nineteenth-century texts the Devonian has been called the "Old Red Age", after the red and brown terrestrial deposits known in the United Kingdom as the Old Red Sandstone in which early fossil discoveries were found. Another common term is "Age of the Fishes", referring to the evolution of several major groups of fish that took place during the period. Older literature on the Anglo-Welsh basin divides it into the Downtonian, Dittonian and Farlovian stages, the latter three of which are placed in the Devonian; the Devonian has erroneously been characterised as a "greenhouse age", due to sampling bias: most of the early Devonian-age discoveries came from the strata of western Europe and eastern North America, which at the time straddled the Equator as part of the supercontinent of Euramerica where fossil signatures of widespread reefs indicate tropical climates that were warm and moderately humid but in fact the climate in the Devonian differed during its epochs and between geographic regions.
For example, during the Early Devonian, arid conditions were prevalent through much of the world including Siberia, North America, China, but Africa and South America had a warm temperate climate. In the Late Devonian, by contrast, arid conditions were less prevalent across the world and temperate climates were more common; the Devonian Period is formally broken into Early and Late subdivisions. The rocks corresponding to those epochs are referred to as belonging to the Lower and Upper parts of the Devonian System. Early DevonianThe Early Devonian lasted from 419.2 ± 2.8 to 393.3 ± 2.5 and began with the Lochkovian stage, which lasted until the Pragian. It spanned from 410.8 ± 2.8 to 407.6 ± 2.5, was followed by the Emsian, which lasted until the Middle Devonian began, 393.3± 2.7 million years ago. During this time, the first ammonoids appeared. Ammonoids during this time period differed little from their nautiloid counterparts; these ammonoids belong to the order Agoniatitida, which in epochs evolved to new ammonoid orders, for example Goniatitida and Clymeniida.
This class of cephalopod molluscs would dominate the marine fauna until the beginning of the Mesozoic era. Middle DevonianThe Middle Devonian comprised two subdivisions: first the Eifelian, which gave way to the Givetian 387.7± 2.7 million years ago. During this time the jawless agnathan fishes began to decline in diversity in freshwater and marine environments due to drastic environmental changes and due to the increasing competition and diversity of jawed fishes; the shallow, oxygen-depleted waters of Devonian inland lakes, surrounded by primitive plants, provided the environment necessary for certain early fish to develop such essential characteristics as well developed lungs, the ability to crawl out of the water and onto the land for short periods of time. Late DevonianFinally, the Late Devonian started with the Frasnian, 382.7 ± 2.8 to 372.2 ± 2.5, during which the first forests took shape on land. The first tetrapods appeared in the fossil record in the ensuing Famennian subdivisi
Scotland is a country, part of the United Kingdom. Sharing a border with England to the southeast, Scotland is otherwise surrounded by the Atlantic Ocean to the north and west, by the North Sea to the northeast and by the Irish Sea to the south. In addition to the mainland, situated on the northern third of the island of Great Britain, Scotland has over 790 islands, including the Northern Isles and the Hebrides; the Kingdom of Scotland emerged as an independent sovereign state in the Early Middle Ages and continued to exist until 1707. By inheritance in 1603, James VI, King of Scots, became King of England and King of Ireland, thus forming a personal union of the three kingdoms. Scotland subsequently entered into a political union with the Kingdom of England on 1 May 1707 to create the new Kingdom of Great Britain; the union created a new Parliament of Great Britain, which succeeded both the Parliament of Scotland and the Parliament of England. In 1801, the Kingdom of Great Britain and Kingdom of Ireland enacted a political union to create a United Kingdom.
The majority of Ireland subsequently seceded from the UK in 1922. Within Scotland, the monarchy of the United Kingdom has continued to use a variety of styles and other royal symbols of statehood specific to the pre-union Kingdom of Scotland; the legal system within Scotland has remained separate from those of England and Wales and Northern Ireland. The continued existence of legal, educational and other institutions distinct from those in the remainder of the UK have all contributed to the continuation of Scottish culture and national identity since the 1707 union with England; the Scottish Parliament, a unicameral legislature comprising 129 members, was established in 1999 and has authority over those areas of domestic policy which have been devolved by the United Kingdom Parliament. The head of the Scottish Government, the executive of the devolved legislature, is the First Minister of Scotland. Scotland is represented in the UK House of Commons by 59 MPs and in the European Parliament by 6 MEPs.
Scotland is a member of the British–Irish Council, sends five members of the Scottish Parliament to the British–Irish Parliamentary Assembly. Scotland is divided into councils. Glasgow City is the largest subdivision in Scotland in terms of population, with Highland being the largest in terms of area. "Scotland" comes from the Latin name for the Gaels. From the ninth century, the meaning of Scotia shifted to designate Gaelic Scotland and by the eleventh century the name was being used to refer to the core territory of the Kingdom of Alba in what is now east-central Scotland; the use of the words Scots and Scotland to encompass most of what is now Scotland became common in the Late Middle Ages, as the Kingdom of Alba expanded and came to encompass various peoples of diverse origins. Repeated glaciations, which covered the entire land mass of modern Scotland, destroyed any traces of human habitation that may have existed before the Mesolithic period, it is believed the first post-glacial groups of hunter-gatherers arrived in Scotland around 12,800 years ago, as the ice sheet retreated after the last glaciation.
At the time, Scotland was covered in forests, had more bog-land, the main form of transport was by water. These settlers began building the first known permanent houses on Scottish soil around 9,500 years ago, the first villages around 6,000 years ago; the well-preserved village of Skara Brae on the mainland of Orkney dates from this period. Neolithic habitation and ritual sites are common and well preserved in the Northern Isles and Western Isles, where a lack of trees led to most structures being built of local stone. Evidence of sophisticated pre-Christian belief systems is demonstrated by sites such as the Callanish Stones on Lewis and the Maes Howe on Orkney, which were built in the third millennium BCE; the first written reference to Scotland was in 320 BC by Greek sailor Pytheas, who called the northern tip of Britain "Orcas", the source of the name of the Orkney islands. During the first millennium BCE, the society changed to a chiefdom model, as consolidation of settlement led to the concentration of wealth and underground stores of surplus food.
The first Roman incursion into Scotland occurred in 79 AD. After the Roman victory, Roman forts were set along the Gask Ridge close to the Highland line, but by three years after the battle, the Roman armies had withdrawn to the Southern Uplands; the Romans erected Hadrian's Wall in northern England and the Limes Britannicus became the northern border of the Roman Empire. The Roman influence on the southern part of the country was considerable, they introduced Christianity to Scotland. Beginning in the sixth century, the area, now Scotland was divided into three areas: Pictland, a patchwork of small lordships in central Scotland; these societies were based on the family unit and had sharp divisions in wealth, although the vast majority were poor and worked full-time in subsistence agriculture. The Picts kept slaves through the ninth century. Gaelic influence over Pictland and Northumbria was facilitated by the large number of Gaelic-speaking clerics working as missionaries. Operating in the sixth ce
In geology and related fields, a stratum is a layer of sedimentary rock or soil, or igneous rock that were formed at the Earth's surface, with internally consistent characteristics that distinguish it from other layers. The "stratum" is the fundamental unit in a stratigraphic column and forms the basis of the study of stratigraphy; each layer is one of a number of parallel layers that lie one upon another, laid down by natural processes. They may extend over hundreds of thousands of square kilometers of the Earth's surface. Strata are seen as bands of different colored or differently structured material exposed in cliffs, road cuts and river banks. Individual bands may vary in thickness from a few millimeters to a kilometer or more. A band may represent a specific mode of deposition: river silt, beach sand, coal swamp, sand dune, lava bed, etc. Geologists categorize them by the material of beds; each distinct layer is assigned to the name of sheet based on a town, mountain, or region where the formation is exposed and available for study.
For example, the Burgess Shale is a thick exposure of dark fossiliferous, shale exposed high in the Canadian Rockies near Burgess Pass. Slight distinctions in material in a formation may be described as "members". Formations are collected into "groups" while groups may be collected into "supergroups". Archaeological horizon Geologic formation Geologic map Geologic unit Law of superposition Bed GeoWhen Database
Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They live in compact colonies of many identical individual polyps. Corals species include the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton. A coral "group" is a colony of myriad genetically identical polyps; each polyp is a sac-like animal only a few millimeters in diameter and a few centimeters in length. A set of tentacles surround a central mouth opening. An exoskeleton is excreted near the base. Over many generations, the colony thus creates a large skeleton characteristic of the species. Individual heads grow by asexual reproduction of polyps. Corals breed sexually by spawning: polyps of the same species release gametes over a period of one to several nights around a full moon. Although some corals are able to catch small fish and plankton using stinging cells on their tentacles, most corals obtain the majority of their energy and nutrients from photosynthetic unicellular dinoflagellates in the genus Symbiodinium that live within their tissues.
These are known as zooxanthellae. Such corals require sunlight and grow in clear, shallow water at depths less than 60 metres. Corals are major contributors to the physical structure of the coral reefs that develop in tropical and subtropical waters, such as the enormous Great Barrier Reef off the coast of Queensland, Australia. Other corals do not rely on zooxanthellae and can live in much deeper water, with the cold-water genus Lophelia surviving as deep as 3,300 metres; some have been found on the Darwin Mounds, northwest of Cape Wrath and others as far north as off the coast of Washington State and the Aleutian Islands. Aristotle's pupil Theophrastus described the red coral, korallion, in his book on stones, implying it was a mineral, but he described it as a deep-sea plant in his Enquiries on Plants, where he mentions large stony plants that reveal bright flowers when under water in the Gulf of Heroes. Pliny the Elder stated boldly that several sea creatures including sea nettles and sponges "are neither animals nor plants, but are possessed of a third nature".
Petrus Gyllius copied Pliny, introducing the term zoophyta for this third group in his 1535 book On the French and Latin Names of the Fishes of the Marseilles Region. Gyllius further noted, following Aristotle, how hard it was to define what was a plant and what was an animal; the Persian polymath Al-Biruni classified sponges and corals as animals, arguing that they respond to touch. People believed corals to be plants until the eighteenth century, when William Herschel used a microscope to establish that coral had the characteristic thin cell membranes of an animal. Presently, corals are classified as certain species of animals within the sub-classes Hexacorallia and Octocorallia of the class Anthozoa in the phylum Cnidaria. Hexacorallia includes the stony corals and these groups have polyps that have a 6-fold symmetry. Octocorallia includes blue coral and soft corals and species of Octocorallia have polyps with an eightfold symmetry, each polyp having eight tentacles and eight mesenteries.
Fire corals are not true corals. Corals are sessile animals and differ from most other cnidarians in not having a medusa stage in their life cycle; the body unit of the animal is a polyp. Most corals are colonial, the initial polyp budding to produce another and the colony developing from this small start. In stony corals known as hard corals, the polyps produce a skeleton composed of calcium carbonate to strengthen and protect the organism; this is deposited by the coenosarc, the living tissue that connects them. The polyps sit in cup-shaped depressions in the skeleton known as corallites. Colonies of stony coral are variable in appearance. In soft corals, there is no stony skeleton but the tissues are toughened by the presence of tiny skeletal elements known as sclerites, which are made from calcium carbonate. Soft corals are variable in form and most are colonial. A few soft corals are stolonate. In some species this is thick and the polyps are embedded; some soft corals are form lobes. Others have a central axial skeleton embedded in the tissue matrix.
This is composed either of a fibrous protein called gorgonin or of a calcified material. In both stony and soft corals, the polyps can be retracted, with stony corals relying on their hard skeleton and cnidocytes for defence against predators, soft corals relying on chemical defences in the form of toxic substances present in the tissues known as terpenoids; the polyps of stony corals have six-fold symmetry. The mouth of each polyp is surrounded by a ring of tentacles. In stony corals these are cylindrical and taper to a point, but in soft corals they are pinnate with side branches known as pinnules. In some tropical species these are reduced to mere stubs and in some they are fused to give a paddle-like appearance. In most corals, the tentacles are retracted by day and spread out at night to catch plankton and other small organisms. Shallow water species of both stony and soft corals can be zooxanthellate, the corals supplementing their plankton diet with t
The Bahamas, known as the Commonwealth of The Bahamas, is a country within the Lucayan Archipelago. The archipelagic state consists of more than 700 islands and islets in the Atlantic Ocean, is located north of Cuba and Hispaniola, northwest of the Turks and Caicos Islands, southeast of the U. S. state of Florida, east of the Florida Keys. The capital is Nassau on the island of New Providence; the designation of "the Bahamas" can refer either to the country or to the larger island chain that it shares with the Turks and Caicos Islands. The Royal Bahamas Defence Force describes the Bahamas territory as encompassing 470,000 km2 of ocean space; the Bahamas is the site of Columbus's first landfall in the New World in 1492. At that time, the islands were inhabited by the Lucayans, a branch of the Arawakan-speaking Taíno people. Although the Spanish never colonised the Bahamas, they shipped the native Lucayans to slavery in Hispaniola; the islands were deserted from 1513 until 1648, when English colonists from Bermuda settled on the island of Eleuthera.
The Bahamas became a British crown colony in 1718. After the American Revolutionary War, the Crown resettled thousands of American Loyalists in the Bahamas. Africans constituted the majority of the population from this period; the slave trade was abolished by the British in 1807. Subsequently, the Bahamas became a haven for freed African slaves. Today, Afro-Bahamians make up nearly 90% of the population; the Bahamas became an independent Commonwealth realm in 1973 with Elizabeth II as its queen. In terms of gross domestic product per capita, the Bahamas is one of the richest countries in the Americas, with an economy based on tourism and finance; the name Bahamas is most derived from either the Taíno ba ha ma, a term for the region used by the indigenous Native Americans, or from the Spanish baja mar reflecting the shallow waters of the area. Alternatively, it may originate from a local name of unclear meaning; the word The constitutes an integral part of the short form of the name and is, capitalised.
So in contrast to "the Congo" and "the United Kingdom", it is proper to write "The Bahamas." The name The Bahamas is thus comparable with certain non-English names that use the definite article, such as Las Vegas or Los Angeles. The Constitution of the Commonwealth of The Bahamas, the country's fundamental law, capitalizes the "T" in "The Bahamas." Taino people moved into the uninhabited southern Bahamas from Hispaniola and Cuba around the 11th century, having migrated there from South America. They came to be known as the Lucayan people. An estimated 30,000 Lucayans inhabited the Bahamas at the time of Christopher Columbus's arrival in 1492. Columbus's first landfall in the New World was on an island; some researchers believe this site to be present-day San Salvador Island, situated in the southeastern Bahamas. An alternative theory holds that Columbus landed to the southeast on Samana Cay, according to calculations made in 1986 by National Geographic writer and editor Joseph Judge, based on Columbus's log.
Evidence in support of this remains inconclusive. On the landfall island, Columbus exchanged goods with them; the Spanish forced much of the Lucayan population to Hispaniola for use as forced labour. The slaves suffered from harsh conditions and most died from contracting diseases to which they had no immunity; the population of the Bahamas was diminished. In 1648, the Eleutherian Adventurers, led by William Sayle, migrated from Bermuda; these English Puritans established the first permanent European settlement on an island which they named Eleuthera—the name derives from the Greek word for freedom. They settled New Providence, naming it Sayle's Island after one of their leaders. To survive, the settlers salvaged goods from wrecks. In 1670, King Charles II granted the islands to the Lords Proprietors of the Carolinas in North America, they rented the islands from the king with rights of trading, appointing governors, administering the country. In 1684 Spanish corsair Juan de Alcon raided Charles Town.
In 1703, a joint Franco-Spanish expedition occupied the Bahamian capital during the War of the Spanish Succession. During proprietary rule, the Bahamas became a haven for pirates, including Blackbeard. To put an end to the'Pirates' republic' and restore orderly government, Great Britain made the Bahamas a crown colony in 1718 under the royal governorship of Woodes Rogers. After a difficult struggle, he succeeded in suppressing piracy. In 1720, Rogers led local militia to drive off a Spanish attack. During the US War of Independence in the late 18th century, the islands became a target for US naval forces under the command of Commodore Esek Hopkins. US Marines occupied the capital of Nassau for 2 weeks. In 1782, following the British defeat at Yorktown, a Spanish fleet appeared off the coast of Nassau; the city surrendered without a fight. Spain returned possession of the Bahamas to Great Britain the following year, u
An orogeny is an event that leads to both structural deformation and compositional differentiation of the Earth's lithosphere at convergent plate margins. An orogen or orogenic belt develops when a continental plate crumples and is pushed upwards to form one or more mountain ranges. Orogeny is the primary mechanism; the word "orogeny" comes from Ancient Greek. Although it was used before him, the term was employed by the American geologist G. K. Gilbert in 1890 to describe the process of mountain building as distinguished from epeirogeny; the formation of an orogen can be accomplished by the tectonic processes such as oceanic subduction or continental subduction convergence of two or more continents for collisional orogeny). Orogeny produces long arcuate structures, known as orogenic belts. Orogenic belts consist of long parallel strips of rock exhibiting similar characteristics along the length of the belt. Although orogenic belts are associated with subduction zones, subduction tectonism may be ongoing or past processes.
The subducting tectonism would consume crust, thicken lithosphere, produce earthquake and volcanoes, build island arcs in many cases. Geologists attribute the arcuate structure to the rigidity of the descending plate, island arc cusps relate to tears in the descending lithosphere; these island arcs may be added to a continental margin during an accretionary orogeny. On the other hand, subduction zones may be reworked at a time due to lithospheric rifting, leading to amphibolite to granulite facies metamorphism of the thinned orogenic crust; the processes of orogeny can take tens of millions of years and build mountains from plains or from the seabed. The topographic height of orogenic mountains is related to the principle of isostasy, that is, a balance of the downward gravitational force upon an upthrust mountain range and the buoyant upward forces exerted by the dense underlying mantle. Rock formations that undergo orogeny are deformed and undergo metamorphism. Orogenic processes may push buried rocks to the surface.
Sea-bottom and near-shore material may cover all of the orogenic area. If the orogeny is due to two continents colliding high mountains can result. An orogenic event may be studied: as a tectonic structural event, as a geographical event, as a chronological event. Orogenic events: cause distinctive structural phenomena related to tectonic activity affect rocks and crust in particular regions, happen within a specific period In general, there are two main types of orogens at convergent plate margins: accretionary orogens, which were produced by subduction of one oceanic plate beneath one continental plate to result in either continental arc magmatism or the accretion of island arc terranes to continental margins. An orogeny produces an orogen, but a range-foreland basin system is only produced on passive plate margins; the foreland basin forms ahead of the orogen due to loading and resulting flexure of the lithosphere by the developing mountain belt. A typical foreland basin is subdivided into a wedge-top basin above the active orogenic wedge, the foredeep beyond the active front, a forebulge high of flexural origin and a back-bulge area beyond, although not all of these are present in all foreland-basin systems.
The basin migrates with the orogenic front and early deposited foreland basin sediments become progressively involved in folding and thrusting. Sediments deposited in the foreland basin are derived from the erosion of the uplifting rocks of the mountain range, although some sediments derive from the foreland; the fill of many such basins shows a change in time from deepwater marine through shallow water to continental sediments. Although orogeny involves plate tectonics, the tectonic forces result in a variety of associated phenomena, including crustal deformation, crustal thickening, crustal thinning and crustal melting as well as magmatism and mineralization. What happens in a specific orogen depends upon the strength and rheology of the continental lithosphere, how these properties change during orogenesis. In addition to orogeny, the orogen is subject to other processes, such as erosion; the sequence of repeated cycles of sedimentation and erosion, followed by burial and metamorphism, by crustal anatexis to form granitic batholiths and tectonic uplift to form mountain chains, is called the orogenic cycle.
For example, the Caledonian Orogeny refers to a series of tectonic events due to the continental collision of Laurentia with Eastern Avalonia and other former fragments of Gondwana in the Early Paleozoic. The Caledonian Orogen resulted from these events and various others that are part of its peculiar orogenic cycle. In summary, an orogeny is an episode of deformation and magmatism at convergent plate margins, during which many geological processes play a role at convergent plate margins; every orogeny has its own orogenic cycle, but composite orogenesis is common at convergent plate margins. Erosion represents a subsequent phase of the orogenic cycle. Erosion removes much of the mountains