The Guiana Shield ( 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. 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 .
13-457: Schwarzwasser is German for "black water" and may refer to: Rivers and streams : Places : In German the term Schwarzwasser may also refer to a blackwater river or blackwater (waste) . Blackwater river A blackwater river is a type of river with a slow-moving channel flowing through forested swamps or wetlands . Most major blackwater rivers are in the Amazon Basin and
26-565: A low conductivity , similar to that of rainwater. Black and white waters differ in their planktonic fauna and flora. Tables 2 and 3 compare the number of planktonic animals caught in black and white water localities only a few meters apart. The black water was not as extreme an example as the Rio Negro system. However, it can be seen that the black water held greater numbers of rotifers but fewer crustaceans and mites . These crustaceans are important foods for larval fish . The zones where
39-486: Is equally rich and 13,367 species of vascular plants 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,
52-825: Is somewhat acidic (typical pH ~6.5) and very clear with a greenish color. The main Amazonian clearwater rivers have their source in the Brazilian Plateau (such as Tapajós , Tocantins , Xingu and some right tributaries of the Madeira ), but some originate in the Guiana Shield (such as Nhamundá , Paru , and Araguari ). Other rivers in Australia may experience infrequent 'blackwater events' associated with flood waters connecting to forested floodplains and these events may be associated with hypoxic waters [low oxygen]. Examples include
65-696: 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. 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%). Diversity of invertebrates remains largely undocumented, but there are several species of endemic butterflies and dung beetles. Plant life
78-702: The Murray River , Edward River , Wakool River and Murrumbidgee River . Guiana Shield 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 . The oldest rocks in
91-758: The Southern United States . The term is used in fluvial studies, geology , geography , ecology , and biology . Not all dark rivers are blackwater in that technical sense. Some rivers in temperate regions, which drain or flow through areas of dark black loam , are simply black due to the color of the soil; these rivers are black mud rivers . There are also black mud estuaries . Blackwater rivers are lower in nutrients than whitewater rivers and have ionic concentrations higher than rainwater. The unique conditions lead to flora and fauna that differ from both whitewater and clearwater rivers . The classification of Amazonian rivers into black, clear, and whitewater
104-679: 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). Pico da Neblina
117-799: 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
130-418: The more neutral white waters. The major difference is the concentrations of sodium , magnesium , calcium , and potassium ; these are very low in black waters. This has ecological implications. Some animals need more calcium than is available in blackwaters, so for example, snails , which need much calcium to build shells, are not abundant in blackwaters. The lack of dissolved ions in black waters results in
143-680: 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. There are three upland areas of
SECTION 10
#1732852596099156-469: The two waters mix are attractive to ostracods and young fish. These mixing zones tend to have many animals. The abundance is shown in Table 3, which compares animals in 10 litres (2.2 imp gal; 2.6 US gal) of water. Blackwater rivers resemble clearwater rivers in having a low conductivity and relatively low levels of dissolved solids , but clearwater rivers have water that often only
169-616: Was first proposed by Alfred Russel Wallace in 1853 based on water colour, but the types were more clearly defined by chemistry and physics by Harald Sioli [ de ] from the 1950s to the 1980s. Although many Amazonian rivers fall clearly into one of these categories, others show a mix of characteristics and may vary depending on season and flood levels. Black and white waters differ significantly in their ionic composition, as shown in Table 1 . Black waters are more acidic , resulting in an aluminum concentration greater than that of
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