Guiana Shield | |
|---|---|
 Political map of the Guiana Shield | |
 | |
| Coordinates:5°08′36″N60°45′45″W / 5.14333°N 60.76250°W /5.14333; -60.76250 | |
| Region | South America |
.JPG)
TheGuiana Shield[1] (French:Plateau des Guyanes, Bouclier guyanais;Dutch:Hoogland van Guyana, Guianaschild;Portuguese:Planalto das Guianas, Escudo das Guianas;Spanish:Escudo guayanés) is one of the threecratons of theSouth American Plate. It is a 1.7 billion-year-oldPrecambrian geologicalformation in northeastSouth America that forms a portion of the northern coast.[2] The higher elevations on theshield are called theGuiana Highlands, which is where the table-like mountains calledtepuis are found. The Guiana Highlands are also the source of some of the world's most well-known waterfalls such asAngel Falls,Kaieteur Falls andCuquenan Falls.
The Guiana Shield underliesGuyana (previouslyBritish Guiana),Suriname (previouslyDutch Guiana), andFrench Guiana (orGuyane), much of southernVenezuela, as well as parts ofColombia andBrazil. The rocks of the Guiana Shield consist of metasediments and metavolcanics (greenstones) overlain by sub-horizontal layers ofsandstones,quartzites,shales andconglomerates intruded by sills of younger mafic intrusives such asgabbros.[3]
The oldest rocks in the shield consist ofArchean Imataca Complex, composed of aquartz-feldspargneiss and subordinatemafic gneiss. The GuriFault marks the southern boundary of the complex. South of that fault are EarlyProterozoic rocks consisting of themetavolcanic PastoraSupergroup and thegraniticplutonic Supamo Complex. The Cuchivero Group consists ofash flowtuff and granitic plutonic rocks. The Early to Middle Proterozoic Roraima Group consists of continentalclastic sedimentary rocks. ThesePrecambrian sediments include quartzsandstones,quartzites, andconglomerates presumed to be 1.8 to 1.4Ga in age.[4][5]
There are three upland areas of the Guiana Shield:
The north-central part of the Guiana Highlands is dominated by high flat-topped peaks calledtepuis, 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 isPico da Neblina in Brazil at 2,995 metres (9,826 ft).[6] Pico da Neblina is the highest summit of the largerNeblina massif, 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.[citation needed]
The Guiana Shield is one of the regions of highestbiodiversity in the world, and has manyendemic species. The region houses over 3000vertebrate species: 1168 fresh water fish, 269 amphibians (54% endemics), 295 reptiles (29%), 1004 birds (7.7%), and 282 mammals (11%).[7][8][9] Diversity of invertebrates remains largely undocumented, but there are several species of endemic butterflies and dung beetles.[10][11]
Plant life is equally rich and 13,367 species ofvascular plants have been found, approximately 40% of which is considered endemic.[12] The shield is overlain by the largest expanse of tropical forest on any Precambrian shield area in the world.[13] Guianan rain forest is similar in nature toAmazonian rain forest and known protected areas include the Iwokrama Forest of central Guyana, Kaieteur,Kanuku National Park of southern Guyana, the UNESCOWorld Heritage SiteCentral Suriname Nature Reserve ofSuriname, theGuiana Amazonian Park inFrench Guiana and theTumucumaque National Park in theAmapá State ofBrazil. In Venezuela the forests are protected byCanaima,Parima-Tapirapeco andSerranía 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 theRamsar Convention.[14]
According to recent researches, although ecosystems of the Guayana Highlands remain vibrant, emerging issues (including "a well-knowninvasive plant elsewhere"Poa annua and "one of the most aggressive weeds"Polypogon elongatus) and infectious faecal bacteriaHelicobacter pylori have been documented.[15]
Media related toGuiana Shield at Wikimedia Commons Media related toGuiana Highlands at Wikimedia Commons Media related toTepuis at Wikimedia CommonsMajor South American geological features | |||||
|---|---|---|---|---|---|
| Tectonic plates |  | ||||
| Cratons andshields | |||||
| Structures undergoingsubduction | |||||
| Faults andshear zones | |||||
| Rifts andgrabens | |||||
| Sedimentary basins | |||||
| Orogenies | |||||
| Metallogenetic provinces | |||||
| Volcanism |
| ||||