The Guiana 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 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.[2] The higher elevations on the
shield are called the Guiana Highlands, which is where the table-like mountains called
tepuis are found. The Guiana Highlands are also the source of some of the world's most well-known waterfalls such as
Angel Falls,
Kaieteur Falls and
Cuquenan Falls.
The Guiana Shield underlies
Guyana (previously British Guiana),
Suriname (previously Dutch Guiana), and
French Guiana (or Guyane), much of southern
Venezuela, as well as parts of
Colombia and
Brazil. The rocks of the Guiana Shield consist of metasediments and metavolcanics (
greenstones) overlain by sub-horizontal layers of
sandstones,
quartzites,
shales and
conglomerates intruded by sills of younger mafic intrusives such as
gabbros.[3]
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 state in Brazil.
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 toward the
Atlantic.
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 north-central part of the
Guiana Highlands is dominated by high flat-topped peaks called
tepuis, 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 2,995 metres (9,826 ft).[6] Pico da Neblina is the highest summit of the larger
Neblina 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]
Ecology
The Guiana Shield is one of the regions of highest
biodiversity in the world, and has many
endemic species. The region houses over 3000
vertebrate 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]
According to recent researches, although ecosystems of the Guayana Highlands remain vibrant, emerging issues (including "a well-known
invasive plant elsewhere" Poa annua and "one of the most aggressive weeds" Polypogon elongatus) and infectious faecal bacteria Helicobacter pylori have been documented.[15]
^Hammond, David S. (ed.) (2005) Tropical Forests of the Guiana Shield CABI Publishing, Wallingford, UK, ISBN
^Gibbs, A.K. and Barron,C.N. (eds) (1993) The Geology of the Guiana Shield Oxford University Press, Oxford, UK, ISBN
^Geology and Mineral Resource Assessment of the Venezuelan Guayana Shield, USGS Bulletin 2062. US Government Printing Office. 1993. pp. 10–15.
^Wray, Robert (2010). Migon, Piotr (ed.). The Gran Sabana: The World's Finest Quartzite Karst?, in Geomorphological Landscapes of the World. Springer. pp. 80–81.
ISBN9789048130542.
^Ferrer-Paris, José R; Lozano, Cecilia; Cardozo-Urdaneta, Arlene; Thomas Cabianca, Arianna (2016). "Indicative response of Oxysternon festivum Linné (Coleoptera: Scarabaidae) to vegetation condition in the basin of the Orinoco river, Venezuela". Journal of Insect Conservation. 20 (3): 527–538.
doi:
10.1007/s10841-016-9886-6.
S2CID17263106.
1 List sourced from volume 1 of Flora of the Venezuelan Guayana; includes landforms that may not strictly conform to the definition of a tepui or
table mountain. 2 Poorly known sites or lower mountains treated as tepuis for historical reasons.