Guiana Shield

{{Short description|Precambrian geological formation in northeast South America}} {{Infobox settlement | name = Guiana Shield | native_name = | other_name = | settlement_type =  | image_skyline = Map of the Guiana shield.png | image_caption = Political map of the Guiana Shield | image_flag = | image_shield = | motto = | nickname = | etymology =  | subdivision_type = Country | subdivision_name = | subdivision_type1 = | subdivision_name1 = | subdivision_type2 = Region | subdivision_name2 = South America | subdivision_type3 = | subdivision_name3 = | subdivision_type4 = | subdivision_name4 =  | image_map = | map_caption = | pushpin_map = | pushpin_relief = | pushpin_map_caption = | coordinates = {{coord|5|08|36|N|60|45|45|W|display=inline,title}} | coordinates_footnotes =  | established_title = | established_date =  | area_footnotes = | area_total_km2 = | area_total_sq_mi = | area_land_sq_mi = | area_water_sq_mi =  | elevation_footnotes = | elevation_m = | elevation_ft =  | population_as_of = | population_footnotes = | population_total = | population_density_km2 = auto | population_density_sq_mi = | population_demonym =  | timezone1 = | utc_offset1 = | timezone1_DST = | utc_offset1_DST =  | postal_code_type = | postal_code = | area_code_type = | area_code = | geocode = | iso_code =  | website = | footnotes = }}

[[File:Cerros de Mavecure (Guainía, Colombia).JPG|thumb|Cerros de Mavecure, Guainía department, Colombia]] [[File:Salto Angel - Cañon del Diablo.JPG|thumb|right|Devil's Canyon in the Canaima National Park, Venezuela]] thumb|right|Map of the Guianas The '''Guiana Shield'''<ref>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 (including most of the state of Roraima) which are on the Guiana Shield.</ref> ({{langx|fr|Plateau des Guyanes, Bouclier guyanais}}; {{langx|nl|Hoogland van Guyana, Guianaschild}}; {{langx|pt|Planalto das Guianas, Escudo das Guianas}}; {{langx|es|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.<ref>Hammond, David S. (ed.) (2005) ''Tropical Forests of the Guiana Shield'' CABI Publishing, Wallingford, UK, ISBN</ref> 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, most of Brazil north of the Amazon River, and parts of eastern Colombia. The first three are called The Guianas, and most of the Guiana Shield coincides with Guiana Island. 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.<ref>Gibbs, A.K. and Barron, C.N. (eds) (1993) ''The Geology of the Guiana Shield'' Oxford University Press, Oxford, UK, ISBN</ref>

== Geology == The oldest rocks in the shield consist of Archean Imataca Complex, composed of a quartz-feldspar gneiss and subordinate mafic gneiss. The Guri Fault marks the southern boundary of the complex. South of that fault are Early Proterozoic rocks consisting of the metavolcanic Pastora Supergroup and the granitic plutonic Supamo Complex. The Cuchivero Group consists of ash flow tuff and granitic plutonic rocks. The Early to Middle Proterozoic Roraima Group consists of continental clastic sedimentary rocks. These Precambrian sediments include quartz sandstones, quartzites, and conglomerates presumed to be 1.8 to 1.4 Ga in age.<ref>{{cite book|title=Geology and Mineral Resource Assessment of the Venezuelan Guayana Shield, USGS Bulletin 2062|date=1993|publisher=US Government Printing Office|pages=10–15}}</ref><ref>{{cite book|last1=Wray|first1=Robert|editor1-last=Migon|editor1-first=Piotr|title=The Gran Sabana: The World's Finest Quartzite Karst?, in Geomorphological Landscapes of the World|date=2010|publisher=Springer|isbn=9789048130542|pages=80–81}}</ref>

== 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 state in Brazil. # The Tumucumaque Uplands 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 {{convert|900|m|ft|0|abbr=on}} 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 {{convert|2995|m|ft}}.<ref name="ibge2016">{{cite press release |url=http://saladeimprensa.ibge.gov.br/noticias?view=noticia&id=1&busca=1&idnoticia=3109 |title=Geociências: IBGE revê as altitudes de site Pontos culminates |language=pt |trans-title=Geosciences: IBGE revises the altitude of seven high points | location=Brasília |publisher=Brazilian Institute of Geography and Statistics (IBGE) |date=2016-02-29 |access-date=2016-03-02 }}</ref> 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|date=August 2015}}

== Ecology == [[File:H chimantensis2.jpg|thumb|upright|''Heliamphora chimantensis'', endemic to the Chimantá Massif (a Venezuelan part of the Guiana Shield)]] The Guiana Shield is one of the world's most biodiverse regions, 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%).<ref>{{cite journal|last1= Hollowell|first1= T.|first2= R.P. |last2= Reynolds|year= 2005|title= Checklist of the Terrestrial Vertebrates of the Guiana Shield|journal= Bulletin of the Biological Society of Washington|volume= 13|url= http://botany.si.edu/bdg/pdf/bswa_13_all.pdf}}</ref><ref>{{cite journal| last1 = Stachowicz | first1 = Izabela| last2 = Ferrer Paris | first2 = José Rafael| last3 = Quiroga-Carmona | first3 = Marcial| last4 = Moran | first4 = Lisandro| last5 = Lozano | first5 = Cecilia| date = 2020| title = Baseline for monitoring and habitat use of medium to large non-volant mammals in Gran Sabana, Venezuela| journal = Therya| volume = 11| issue = 2| pages = 169–179| doi = 10.12933/therya-20-891| doi-access = free| hdl = 1959.4/unsworks_67008| hdl-access = free}}</ref><ref>{{cite journal|last1= Vari|first1= R.P.|first2= C.J.|last2= Ferraris Jr.|first3= A.|last3= Radosavljevic|first4= V.A.|last4= Funk|year= 2009|title= Checklist of the freshwater fishes of the Guiana Shield|journal= Bulletin of the Biological Society of Washington|volume= 17|url= http://botany.si.edu/bdg/pdf/bswa_fish-chcklst_2009-complete.pdf}}</ref> Diversity of invertebrates remains largely undocumented, but there are several species of endemic butterflies and dung beetles.<ref name="IndicativeResponse">{{cite journal|last1=Ferrer-Paris|first1=José R|last2=Lozano|first2=Cecilia|last3=Cardozo-Urdaneta|first3=Arlene|last4=Thomas Cabianca|first4=Arianna|title=Indicative response of ''Oxysternon festivum'' Linné (Coleoptera: Scarabaidae) to vegetation condition in the basin of the Orinoco river, Venezuela|journal=Journal of Insect Conservation|volume=20 |issue=3|pages=527–538|doi=10.1007/s10841-016-9886-6|year=2016|s2cid=17263106}}</ref><ref name="ViloriaPantepui">{{cite journal|last1=Costa|first1=Mauro|last2=Viloria|first2=Ángel L.|last3=Hubber|first3=Otto|last4=Attal|first4=Stéphane|last5=Orellana|first5=Andrés|title=Lepidoptera del Pantepui. Parte I: Endemismo y caracterización biogeográfica|journal=Entomotropica|date=2013|volume=28|issue=3|pages=193–217|url=http://www.entomotropica.org/index.php/entomotropica/article/view/414/449|access-date=25 June 2016|archive-url=https://web.archive.org/web/20160827045133/http://www.entomotropica.org/index.php/entomotropica/article/view/414/449|archive-date=27 August 2016|url-status=dead}}</ref>

Plant life is equally rich and 13,367 species of vascular plants have been found, approximately 40% of which is considered endemic.<ref>{{cite journal|last1= Funk|first1= V.|first2= T.|last2= Hollowell|first3= P.|last3= Berry|first4= C.|last4= Kelloff|first5= S.N.|last5= Alexander|year= 2007|title=Checklist of the Plants of the Guiana Shield (Venezuela: Amazonas, Bolivar, Delta Amacuro; Guyana, Surinam, French Guiana)|journal= Contributions from the United States National Herbarium|volume= 55|url= http://botany.si.edu/bdg/pdf/vol55web.pdf}}</ref> The shield is overlain by the largest expanse of tropical forest on any Precambrian shield area in the world.<ref>Hammond, David S. (ed.) (2005) ''Tropical Forests of the Guiana Shield'' CABI Publishing, Wallingford, UK, ISBN</ref> 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 Central Suriname Nature Reserve of Suriname, the Guiana Amazonian Park in French Guiana and the Tumucumaque National Park in the Amapá State of Brazil. 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.<ref>{{Cite web | url=http://www.ramsar.org/es/complejo-de-humedales-de-la-estrella-fluvial-in%C3%ADrida-efi | title=Colombia | Ramsar}}</ref>

According to recent researches, although ecosystems of the Guiana 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.<ref>{{cite journal |last1= Rull|first1= V.|last2= Vegas-Vilarrúbia|first2= T.|last3= Safont|first3= E.|date= 2016|title= The Lost World's pristinity at risk|journal= Diversity and Distributions|volume= 22|issue= 10|pages= 995–999|doi= 10.1111/ddi.12469|bibcode= 2016DivDi..22..995R|url= https://digital.csic.es/bitstream/10261/137349/3/Rull_Diversity_and_Distributions_22_995_postprint.pdf|hdl= 10261/137349|s2cid= 23002053|hdl-access= free}} </ref>

== See also == *{{annotated link|Gran Sabana}} *{{annotated link|Tepui}} *{{annotated link|Canadian Shield}} *{{annotated link|Caribbean South America}} *{{annotated link|Mount Roraima}} *{{annotated link|Pico da Neblina}} *{{annotated link|Great American Interchange}} *{{annotated link|Geography of South America}}

== References ==  {{reflist}}

== External links == * {{Commons category-inline|Guiana Shield}} * {{Commons-inline|Guiana Highlands}} * {{Commons category-inline|Tepuis}}

{{Major South American geological formations}} {{Physiographic regions}} {{Tepuis|state=collapsed}} {{Geographical Regions of Venezuela}} {{Authority control}}

Category:Shields (geology) . Shield Category:Plateaus of South America Category:Plateaus of Brazil Category:Plateaus of Venezuela Category:Geographical regions of Venezuela Category:Geography of Colombia Category:Geography of French Guiana Category:Geography of Guyana Category:Geography of Suriname Category:Natural regions of South America Category:Geology of South America Category:Geology of Brazil Category:Geology of Colombia Category:Geology of French Guiana Category:Geology of Guyana Category:Geology of Suriname Category:Geology of Venezuela . Category:Natural history of South America Category:North Region, Brazil Category:Geography of Amapá Category:Geography of Pará Category:Geography of Roraima Category:Precambrian South America