Guiana Shield
From Wikipedia, the free encyclopedia
The Guiana[1] Shield (Spanish: Guayana) is one of the three cratons of the South American Plate. It is a 1.7 billion year old Precambrian geological formation in northeast South America that forms a portion of the northern coast. The higher elevations on the shield are called the Guiana Highlands, which is where the impressive and mysterious table-like mountains called tepuis are found. The Guiana Highlands are also the source of some of the world's most spectacular waterfalls such as Angel Falls, Kaieteur Falls and Kuquenan Falls.
The Guiana Shield underlies Guyana (previously British Guiana), Suriname (previously Dutch Guiana) and French Guiana (or Guyane), as well as parts of Colombia, Venezuela and Brazil. The rocks of the Guiana Shield consist of metasediments and metavolcanics (greenstones) overlain by quasi-horizontal layers of sandstones, quartzites, shales and conglomerates intruded by sills of younger mafic intrusives such as gabbros.
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[edit] Geomorphology
There are three upland areas of the Guiana Shield. (1) The Guaiana Highlands proper are in Venezuela east of the Orinoco and extend across much of westcentral Guyana and into the northern Roraima state in Brazil. (2) The Tumucumaque Uplands which are a series of central massifs in an arc from the Wilhelmina Mountains 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 and Amapá states of Brazil. From this arc, the southern uplands slope gently downwards towards the Amazon River and the northern uplands slope gently downwards towards the Atlantic. (3) The Chiribiquete Plateau is a sandstone topped plateau with an elevation of 900 m (2,953 ft) that forms the western edge of the shield. The plateau is separated from the eastern Andes by the thick Neogene sediments of the Sub-Andean Trough that runs along the northern and western rim of the Guiana Shield.
The Guiana Highlands are dominated by the high flat-topped peaks, the tepui, 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 tepui is Pico da Neblina at 2,994m.
[edit] Ecology
The Guiana Shield is one of the regions of highest biodiversity in the world. The Shield has 1400 vertebrate species and 1680 bird species.[citation needed] The Shield is overlain by the largest expanse of undisturbed tropical rain forest in the world.[2] Guianan rain forest is similar in nature to Amazonian rain forest and known Protected Areas include the Iwokrama Forest of central Guyana and the Kanuku National Park of southern Guyana. In Venezuela the forests are partially protected by the Canaima National Park (VE) and the Kaieteur National Park (GY).
[edit] References
- ^ The term Guiana or The Guianas is often used as a collective name for Guyana, Suriname and French Guiana, and sometimes even includes the portions of Colombia, Venezuela and Brazil which are on the Guiana Shield.
- ^ Hammond, David S. (ed.) (2005) Tropical Rainforests of the Guianan Shield CABI Publishing, Wallingford, UK, ISBN
[edit] See also
- Tepui
- Canadian Shield
- Caribbean South America
- Monte Roraima
- Pico da Neblina
- Great American Interchange
- Geography of South America
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