South America’s ancient Guiana Shield still holds tepui country
The Guiana Shield is one of South America’s three continental cratons, flooring Guyana, Suriname, French Guiana, southern Venezuela, northern Brazil, and eastern Colombia. Archean Imataca gneisses and Proterozoic belts make it a deep-time highland of tepuis and gold.
Three upland areas stand out. The Guiana Highlands run east of the Orinoco into Guyana and Brazil’s Roraima state; the Tumucumaque massifs arc from Suriname’s Wilhelmina range along the borders through the Acarai and Tumuc-Humac mountains; and in Colombia the Chiribiquete sandstone plateau, near 900 metres, is separated from the Andes by thick sub-Andean sediments. The oldest rocks, the Archean Imataca gneisses, end to the south at the Guri Fault.
Flat-topped tepuis of the Roraima supergroup dominate the north-central highlands, while rounded granite domes of the Parguaza and Imataca complexes rise at the northern and southwestern edges. Its highest point, Brazil’s 2,995-metre Pico da Neblina, is the top of a heavily eroded sandstone massif straddling the Venezuela–Brazil border.
Over 3,000 vertebrate species live here: 1,168 freshwater fish, 269 amphibians of which more than half are endemic, 295 reptiles, 1,004 birds, and 282 mammals. Botanists have recorded 13,367 vascular plants, around 40 per cent found nowhere else, and invertebrates such as butterflies and dung beetles include local endemics still barely catalogued. Among the named residents are the tiny Guiana Shield frog and the greater long-nosed armadillo.
The shield carries the largest tropical forest on any Precambrian shield in the world, similar to Amazonian rainforest, protected in places such as Guyana’s Iwokrama Forest, Kaieteur, and Kanuku Mountains and Suriname’s Central Suriname Nature Reserve, a World Heritage Site. Researchers have nonetheless found invasive grasses such as annual meadow grass and Polypogon elongatus in the highlands, along with the stomach bacterium Helicobacter pylori.
Source: Guiana Shield
