The Guiana Shield (; ; ; ) is one of the three

craton A craton ( , , or ; from "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 rifting of contine ...

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 ...

. It is a 1.7 billion-year-old

Precambrian The Precambrian ( ; or pre-Cambrian, sometimes abbreviated pC, 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 t ...

geological formation in northeast

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

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 like spears or long ranged projectiles suc ...

are called the Guiana Highlands, which is where the table-like mountains called

tepui A tepui , or tepuy (), is a member of a family of table-top mountains or mesas found in northern South America, especially in Venezuela, western Guyana, and northern Brazil. The word tepui means "house of the gods" in the native tongue of the ...

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 (; Pemon: ''Kerepakupai Merú'' or ''Parakupá Vená'') is a waterfall in Venezuela. It is the world's tallest uninterrupted waterfall, with a height of , and a plunge of . The waterfall drops over the edge of the Auyán-tepui m ...

Kaieteur Falls Kaieteur Falls is one of the most powerful single-drop waterfalls in the world. It is located on the Potaro River in Kaieteur National Park, central Essequibo Territory, Guyana. It is 226 metres (741 ft) high when measured from its plunge ...

and Cuquenan Falls. The Guiana Shield underlies

Guyana Guyana, officially the Co-operative Republic of Guyana, is a country on the northern coast of South America, part of the historic British West Indies. entry "Guyana" Georgetown, Guyana, Georgetown is the capital of Guyana and is also the co ...

(previously ''British Guiana''),

Suriname Suriname, officially the Republic of Suriname, is a country in northern South America, also considered as part of the Caribbean and the West Indies. It is a developing country with a Human Development Index, high level of human development; i ...

(previously ''Dutch Guiana''), and

French Guiana French Guiana, or Guyane in French, is an Overseas departments and regions of France, overseas department and region of France located on the northern coast of South America in the Guianas and the West Indies. Bordered by Suriname to the west ...

(or ''Guyane''), much of southern

Venezuela Venezuela, officially the Bolivarian Republic of Venezuela, is a country on the northern coast of South America, consisting of a continental landmass and many Federal Dependencies of Venezuela, islands and islets in the Caribbean Sea. It com ...

, as well as parts of

Colombia Colombia, officially the Republic of Colombia, is a country primarily located in South America with Insular region of Colombia, insular regions in North America. The Colombian mainland is bordered by the Caribbean Sea to the north, Venezuel ...

and

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

. 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, cemented together by another mineral. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed o ...

, quartzites,

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, especial ...

and conglomerates intruded by sills of younger mafic intrusives such as

gabbro Gabbro ( ) is a phaneritic (coarse-grained and magnesium- and iron-rich), mafic intrusive igneous rock formed from the slow cooling magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is ch ...

Geology

The oldest rocks in the shield consist of

Archean The Archean ( , also spelled Archaean or Archæan), in older sources sometimes called the Archaeozoic, is the second of the four geologic eons of Earth's history of Earth, history, preceded by the Hadean Eon and followed by the Proterozoic and t ...

Imataca Complex, composed of a

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

feldspar Feldspar ( ; sometimes spelled felspar) is 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 ''plagiocl ...

gneiss Gneiss (pronounced ) 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. This rock is formed under p ...

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 the third of the four geologic eons of Earth's history, spanning the time interval from 2500 to 538.8 Mya, and is the longest eon of Earth's geologic time scale. It is preceded by the Archean and followed by the Phanerozo ...

rocks consisting of the metavolcanic Pastora Supergroup and the

granitic A granitoid is a broad term referring to a diverse group of coarse-grained igneous rocks that are widely distributed across the globe, covering a significant portion of the Earth's exposed surface and constituting a large part of the continental ...

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: Marc ...

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 volcanic gas, gas and volcanic matter (collectively known as tephra) that flows along the ground away from a volcano at average ...

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 co ...

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 b ...

ary rocks. These

sediments include quartz

quartzite Quartzite is a hard, non- foliated metamorphic rock that 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 tecton ...

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 The Orinoco () is one of the longest rivers in South America at . Its drainage basin, sometimes known as the Orinoquia, covers approximately 1 million km2, with 65% of it in Venezuela and 35% in Colombia. It is the List of rivers by discharge, f ...

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 t ...

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 Shi ...

of south-central Suriname, along the southern boundary of Suriname and Guyana, forming the Acarai Mountains of Roraima state and the Tumuc-Humac Mountains 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 st ...

and

Amapá Amapá (; ) is one of the 26 federative units of Brazil, states of Brazil. It is in the North Region, Brazil, North Region of Brazil. It is Federative units of Brazil#List, the second-least populous state and the eighteenth-largest state by area ...

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 oceanic divisions, with an area of about . It covers approximately 17% of Earth's surface and about 24% of its water surface area. During the Age of Discovery, it was known for se ...

. # The Chiribiquete Plateau is a sandstone topped

plateau In geology and physical geography, a plateau (; ; : plateaus or plateaux), 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. ...

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 Mountain Range (; ) are the List of longest mountain chains on Earth, longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range ...

by the thick

Neogene The Neogene ( ,) 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 million years ago. It is the second period of th ...

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

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 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 can ...

, 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 is the variability of life, life on Earth. It can be measured on various levels. There is for example genetic variability, species diversity, ecosystem diversity and Phylogenetics, phylogenetic diversity. Diversity is not distribut ...

in the world, and has many

endemic Endemism is the state of a species being found only 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 foun ...

species. The region houses over 3000

vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

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 (; ), are plants that have lignin, lignified tissues (the xylem) for conducting water and minerals throughout the plant. They also have a specialized non-lignified Ti ...

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 World Heritage Sites are landmarks and areas with legal protection under an treaty, international treaty administered by UNESCO for having cultural, historical, or scientific significance. The sites are judged to contain "cultural and natural ...

Central Suriname Nature Reserve The Central Suriname Nature Reserve () is a conservation unit in Suriname. It preserves an area of tropical rainforest. The reserve is in pristine condition. History The Central Suriname Nature Reserve was created in 1998 by Conservation Intern ...

, the

Guiana Amazonian Park Guiana Amazonian Park () is the largest national park of France, aiming at protecting part of the Amazonian forest located in French Guiana which covers 41% of the region. It is the largest park in France as well as the largest park in the Eu ...

and the Tumucumaque National Park in the

State of

. 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 site, Ramsar sites (wetlands). It is also known as the Convention on We ...

. 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'') and infectious faecal bacteria ''

Helicobacter pylori ''Helicobacter pylori'', previously known as ''Campylobacter pylori'', is a gram-negative, Flagellum#bacterial, flagellated, Bacterial cellular morphologies#Helical, helical bacterium. Mutants can have a rod or curved rod shape that exhibits l ...

'' have been documented.

References

External links

* * * {{Authority control Shields (geology) .

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 like spears or long ranged projectiles suc ...

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

Geology

Geomorphology

Ecology

See also

References

External links