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The Guiana Shield (french: Plateau des Guyanes, Bouclier guyanais; nl, Hoogland van Guyana, Guianaschild; pt, Planalto das Guianas, Escudo das Guianas; es, Escudo guayanés) is one of the three
craton A craton (, , or ; from grc-gre, κράτος "strength") is an old and stable part of the continental lithosphere, which consists of Earth's two topmost layers, the crust and the uppermost mantle. Having often survived cycles of merging and ...
s of the
South American Plate The South American Plate is a major tectonic plate which includes the continent of South America as well as a sizable region of the Atlantic Ocean seabed extending eastward to the African Plate, with which it forms the southern part of the Mid-A ...
. It is a 1.7 billion-year-old
Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...
geological
formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondar ...
in northeast
South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...
that forms a portion of the northern coast. The higher elevations on the
shield A shield is a piece of personal armour held in the hand, which may or may not be strapped to the wrist or forearm. Shields are used to intercept specific attacks, whether from close-ranged weaponry or projectiles such as arrows, by means of a ...
are called the Guiana Highlands, which is where the table-like mountains called
tepui A tepui , or tepuy (), is a table-top mountain or mesa found in South America, especially in Venezuela and western Guyana. The word tepui means "house of the gods" in the native tongue of the Pemon, the indigenous people who inhabit the Gran S ...
s are found. The Guiana Highlands are also the source of some of the world's most well-known waterfalls such as
Angel Falls Angel Falls ( es, Salto Ángel; Pemon language: ''Kerepakupai Merú'' meaning "waterfall of the deepest place", or ''Parakupá Vená'', meaning "the fall from the highest point") is a waterfall in Venezuela. It is the List of waterfalls by hei ...
,
Kaieteur Falls Kaieteur is the world's largest single drop waterfall. Located on the Potaro River in the Kaieteur National Park, it sits in a section of the Amazon rainforest included in the Potaro-Siparuni region of Guyana. It is 226 metres (741 ft) ...
and
Cuquenan Falls Kukenan Falls (or Salto Kukenan, Kukenaam, Cuquenan or similar) is the second tallest major waterfall in Venezuela after Angel Falls. It is also the second tallest free-leaping waterfall in the world. Overall, it is usually cited as the 11th highe ...
. The Guiana Shield underlies
Guyana Guyana ( or ), officially the Cooperative Republic of Guyana, is a country on the northern mainland of South America. Guyana is an indigenous word which means "Land of Many Waters". The capital city is Georgetown. Guyana is bordered by the ...
(previously British Guiana),
Suriname Suriname (; srn, Sranankondre or ), officially the Republic of Suriname ( nl, Republiek Suriname , srn, Ripolik fu Sranan), is a country on the northeastern Atlantic coast of South America. It is bordered by the Atlantic Ocean to the north ...
(previously Dutch Guiana) and
French Guiana French Guiana ( or ; french: link=no, Guyane ; gcr, label=French Guianese Creole, Lagwiyann ) is an overseas departments and regions of France, overseas department/region and single territorial collectivity of France on the northern Atlantic ...
(or Guyane), much of southern
Venezuela Venezuela (; ), officially the Bolivarian Republic of Venezuela ( es, link=no, República Bolivariana de Venezuela), is a country on the northern coast of South America, consisting of a continental landmass and many islands and islets in th ...
, as well as parts of
Colombia Colombia (, ; ), officially the Republic of Colombia, is a country in South America with insular regions in North America—near Nicaragua's Caribbean coast—as well as in the Pacific Ocean. The Colombian mainland is bordered by the Car ...
and
Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
. The rocks of the Guiana Shield consist of metasediments and metavolcanics ( greenstones) overlain by sub-horizontal layers of
sandstones Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) b ...
,
quartzites Quartzite is a hard, non- foliated metamorphic rock which was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to ...
,
shales Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especiall ...
and conglomerates intruded by sills of younger mafic intrusives such as
gabbro Gabbro () is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is che ...
s.


Geology

The oldest rocks in the shield consist of
Archean The Archean Eon ( , also spelled Archaean or Archæan) is the second of four geologic eons of Earth's history, representing the time from . The Archean was preceded by the Hadean Eon and followed by the Proterozoic. The Earth Earth ...
Imataca Complex, composed of a
quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...
-
feldspar Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) feldsp ...
gneiss Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures an ...
and subordinate
mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include ...
gneiss. The Guri Fault marks the southern boundary of the complex. South of that fault are Early
Proterozoic The Proterozoic () is a geological eon spanning the time interval from 2500 to 538.8million years ago. It is the most recent part of the Precambrian "supereon". It is also the longest eon of the Earth's geologic time scale, and it is subdivided ...
rocks consisting of the
metavolcanic Metavolcanic rock is volcanic rock that shows signs of having experienced metamorphism. In other words, the rock was originally produced by a volcano, either as lava or tephra. The rock was then subjected to high pressure, high temperature or both ...
Pastora
Supergroup Supergroup or super group may refer to: * Supergroup (music), a music group formed by artists who are already notable or respected in their fields * Supergroup (physics), a generalization of groups, used in the study of supersymmetry * Supergroup ...
and the
granitic A granitoid is a generic term for a diverse category of coarse-grained igneous rocks that consist predominantly of quartz, plagioclase, and alkali feldspar. Granitoids range from plagioclase-rich tonalites to alkali-rich syenites and from quart ...
plutonic Intrusive rock is formed when magma penetrates existing rock, crystallizes, and solidifies underground to form '' intrusions'', such as batholiths, dikes, sills, laccoliths, and volcanic necks.Intrusive RocksIntrusive rocks accessdate: March ...
Supamo Complex. The Cuchivero Group consists of
ash flow A pyroclastic flow (also known as a pyroclastic density current or a pyroclastic cloud) is a fast-moving current of hot gas and volcanic matter (collectively known as tephra) that flows along the ground away from a volcano at average speeds of b ...
tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock cont ...
and granitic plutonic rocks. The Early to Middle Proterozoic Roraima Group consists of continental
clastic sediment Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus,Essentials of Geology, 3rd Ed, Stephen Marshak, p. G-3 chunks, and smaller grains of rock broken off other rocks ...
ary rocks. These
Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...
sediments include quartz
sandstones Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) b ...
,
quartzite Quartzite is a hard, non- foliated metamorphic rock which was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tect ...
s, and conglomerates presumed to be 1.8 to 1.4 Ga in age.


Geomorphology

There are three upland areas of the Guiana Shield: # The Guiana Highlands proper are in Venezuela east of the Orinoco and extend across much of west-central Guyana and into the northern
Roraima Roraima (, ) is one of the 26 states of Brazil. Located in the country's North Region, it is the northernmost and most geographically and logistically isolated state in Brazil. It is bordered by the state of Pará to the southeast, Amazonas ...
state in Brazil. # The Tumucumaque Uplands which are a series of central massifs in an arc from the
Wilhelmina Mountains The Wilhelminagebergte () is a mountain range in the district of Sipaliwini in central Suriname. It extends about from west to east. It is named after Queen Wilhelmina. The Wilhelminagebergte is part of the Tumucumaque Uplands of the Guiana Shie ...
of south-central Suriname, along the southern boundary of Suriname and Guyana, forming the Acarai Mountains of Roraima state and the
Tumuc-Humac Mountains The Tumuk Humak Mountains ( nl, Toemoek-Hoemakgebergte, pt, Serra do Tumucumaque, french: Monts Tumuc Humac) are a mountain range in South America, stretching about east–west in the border area between Brazil in the south and Suriname and F ...
of
Pará Pará is a Federative units of Brazil, state of Brazil, located in northern Brazil and traversed by the lower Amazon River. It borders the Brazilian states of Amapá, Maranhão, Tocantins (state), Tocantins, Mato Grosso, Amazonas (Brazilian state) ...
and
Amapá Amapá () is one of the 26 states of Brazil. It is in the northern region of Brazil. It is the second least populous state and the eighteenth largest by area. Located in the far northern part of the country, Amapá is bordered clockwise by Fr ...
states of Brazil. From this arc, the southern uplands slope gently downwards towards the Amazon River and the northern uplands slope gently downwards toward the
Atlantic The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe an ...
. # The Chiribiquete Plateau is a sandstone topped
plateau In geology and physical geography, a plateau (; ; ), also called a high plain or a tableland, is an area of a highland consisting of flat terrain that is raised sharply above the surrounding area on at least one side. Often one or more sides ha ...
with an elevation of that forms the western edge of the shield. The plateau is separated from the eastern
Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...
by the thick
Neogene The Neogene ( ), informally Upper Tertiary or Late Tertiary, is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period Mya. ...
sediments of the Sub-Andean Trough that runs along the northern and western rim of the Guiana Shield. The north-central part of the Guiana Highlands is dominated by high flat-topped peaks called
tepui A tepui , or tepuy (), is a table-top mountain or mesa found in South America, especially in Venezuela and western Guyana. The word tepui means "house of the gods" in the native tongue of the Pemon, the indigenous people who inhabit the Gran S ...
s, of the Roraima supergroup and Quasi-Roraima formation, and the rounded granite peaks of the Parguaza and Imataca complexes to the north and southwestern edges of the area. The highest point in the shield is
Pico da Neblina Pico da Neblina (, literally translatable to ''Mist Peak'') is the highest peak in Brazil, above sea level, in the Serra da Neblina, part of the Serra do Imeri, a section of the Guiana Highlands on the Brazil-Venezuela border. As determine ...
in Brazil at . Pico da Neblina is the highest summit of the larger
Neblina massif Cerro de la Neblina (lit. "Mountain of the Mist"), also known as Serra da Neblina in Brazil and Sierra de la Neblina in Venezuela, is a sandstone massif located in the northern Amazon Basin. It is a tilted, heavily eroded plateau, with a deep ca ...
, a highly eroded sandstone plateau that straddles the Venezuela-Brazil border and that has lost the typical tabletop shape of the other tepuis in the region.


Ecology

The Guiana Shield is one of the regions of highest
biodiversity Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (''genetic variability''), species (''species diversity''), and ecosystem (''ecosystem diversity'') l ...
in the world, and has many
endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...
species. The region houses over 3000
vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...
species: 1168 fresh water fish, 269 amphibians (54% endemics), 295 reptiles (29%), 1004 birds (7.7%), and 282 mammals (11%). Diversity of invertebrates remains largely undocumented, but there are several species of endemic butterflies and dung beetles. Plant life is equally rich and 13,367 species of
vascular plant Vascular plants (), also called tracheophytes () or collectively Tracheophyta (), form a large group of land plants ( accepted known species) that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They al ...
s have been found, approximately 40% of which is considered endemic. The shield is overlain by the largest expanse of tropical forest on any Precambrian shield area in the world. Guianan rain forest is similar in nature to Amazonian rain forest and known protected areas include the Iwokrama Forest of central Guyana, Kaieteur, Kanuku National Park of southern Guyana, the UNESCO
World Heritage Site A World Heritage Site is a landmark or area with legal protection by an international convention administered by the United Nations Educational, Scientific and Cultural Organization (UNESCO). World Heritage Sites are designated by UNESCO for h ...
Central Suriname Nature Reserve The Central Suriname Nature Reserve ( nl, Centraal Suriname Natuurreservaat (CSNR)) is a conservation unit in Suriname. It preserves an area of tropical rainforest. The reserve is in pristine condition. History The Central Suriname Nature Reserv ...
of
Suriname Suriname (; srn, Sranankondre or ), officially the Republic of Suriname ( nl, Republiek Suriname , srn, Ripolik fu Sranan), is a country on the northeastern Atlantic coast of South America. It is bordered by the Atlantic Ocean to the north ...
, the
Guiana Amazonian Park Guiana Amazonian Park (french: Parc amazonien de Guyane) is the largest List of national parks of France, national park of France, aiming at protecting part of the Amazonian forest located in French Guiana which covers 41% of the region of Fran ...
in
French Guiana French Guiana ( or ; french: link=no, Guyane ; gcr, label=French Guianese Creole, Lagwiyann ) is an overseas departments and regions of France, overseas department/region and single territorial collectivity of France on the northern Atlantic ...
and the
Tumucumaque National Park The Tumucumaque Mountains National Park ( pt, Parque Nacional Montanhas do Tumucumaque; ) is situated in the Amazon Rainforest in the Brazilian states of Amapá and Pará. It is bordered to the north by French Guiana and Suriname. History ...
in the
Amapá Amapá () is one of the 26 states of Brazil. It is in the northern region of Brazil. It is the second least populous state and the eighteenth largest by area. Located in the far northern part of the country, Amapá is bordered clockwise by Fr ...
State of
Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
. In Venezuela the forests are protected by Canaima, Parima-Tapirapeco and Serranía de la Neblina national parks. In 2014, the Government of Colombia designated a 250 hectare area of the Guiana Shield, as a Ramsar Wetland, thus becoming a protected area of international importance in accordance to the
Ramsar Convention The Ramsar Convention on Wetlands of International Importance Especially as Waterfowl Habitat is an international treaty for the conservation and sustainable use of Ramsar sites (wetlands). It is also known as the Convention on Wetlands. It i ...
. According to recent researches, although ecosystems of the Guayana Highlands remain vibrant, emerging issues (including "a well-known invasive plant elsewhere" ''
Poa annua ''Poa annua'', or annual meadow grass (known in America more commonly as annual bluegrass or simply poa), is a widespread low-growing turfgrass in temperate climates. Notwithstanding the reference to annual plant in its name, perennial bio-types ...
'' and "one of the most aggressive weeds" ''
Polypogon elongatus ''Polypogon'' is a nearly cosmopolitan genus of plants in the grass family, commonly known beard grass or rabbitsfoot grass. Description ''Polypogon'' species vary in appearance; some are erect, while others drape over the ground in waves. M ...
'') and infectious faecal bacteria ''
Helicobacter pylori ''Helicobacter pylori'', previously known as ''Campylobacter pylori'', is a gram-negative, microaerophilic, spiral (helical) bacterium usually found in the stomach. Its helical shape (from which the genus name, helicobacter, derives) is though ...
'' have been documented.


See also

* * * * * * * *


References


External links

* * * {{Authority control Cratons .
Shield A shield is a piece of personal armour held in the hand, which may or may not be strapped to the wrist or forearm. Shields are used to intercept specific attacks, whether from close-ranged weaponry or projectiles such as arrows, by means of a ...
Plateaus of South America Plateaus of Brazil Plateaus of Venezuela Geographical regions of Venezuela Geography of Colombia Geography of French Guiana Geography of Guyana Geography of Suriname Natural regions of South America Geology of South America Geology of Brazil Geology of Colombia Geology of French Guiana Geology of Guyana Geology of Suriname Geology of Venezuela . Natural history of South America North Region, Brazil Geography of Amapá Geography of Pará Geography of Roraima Precambrian South America