Guiana Shield

The Guiana Shield is an ancient geological feature in northeastern South America, dating back 1.7 billion years to the Precambrian era. It is one of the three cratons that make up the South American plate and stretches along part of the continent’s northern coast. The shield’s higher elevations are known as the Guiana Highlands, home to flat-topped, table-like mountains called tepuis. These highlands also give rise to several famous waterfalls, including Angel Falls, Kaieteur Falls, and Cuquenan Falls.

The shield lies beneath Guyana (formerly British Guiana), Suriname (formerly Dutch Guiana), and French Guiana (or Guyane), as well as much of southern Venezuela, most of Brazil north of the Amazon River, and parts of eastern Colombia. The first three territories are collectively called The Guianas, and most of the shield overlaps with what is known as Guiana Island. Its rocks are made up of metasediments and metavolcanics (greenstones), topped by nearly horizontal layers of sandstones, quartzites, shales, and conglomerates, with younger mafic intrusives like gabbros cutting through as sills.

**Geology** The shield’s oldest rocks belong to the Archean Imataca Complex, which consists of quartz-feldspar gneiss and some mafic gneiss. The Guri Fault marks the southern edge of this complex. South of the fault lie Early Proterozoic rocks, including the metavolcanic Pastora Supergroup and the granitic plutonic Supamo Complex. The Cuchivero Group is made up of ash flow tuff and granitic plutonic rocks. The Early to Middle Proterozoic Roraima Group consists of continental clastic sedimentary rocks—quartz sandstones, quartzites, and conglomerates—thought to be between 1.8 and 1.4 billion years old.

**Geomorphology** The Guiana Shield has three main upland areas. The Guiana Highlands proper sit in Venezuela east of the Orinoco River, stretching across much of west-central Guyana and into northern Roraima state in Brazil. The Tumucumaque Uplands form a series of central massifs in an arc from the Wilhelmina Mountains of south-central Suriname, along the southern borders of Suriname and Guyana, and into the Acarai Mountains of Roraima state and the Tumuc-Humac Mountains of Pará and Amapá states in Brazil. From this arc, the southern slopes descend gently toward the Amazon River, while the northern slopes slope gently toward the Atlantic. The Chiribiquete Plateau is a sandstone-topped plateau about 900 meters (2,953 feet) high, forming the shield’s western edge. It is separated from the eastern Andes by a thick layer of Neogene sediments in the Sub-Andean Trough, which runs along the shield’s northern and western rim.

The north-central part of the Guiana Highlands is dominated by high, flat-topped tepuis from the Roraima supergroup and Quasi-Roraima formation, along with rounded granite peaks from the Parguaza and Imataca complexes to the north and southwest. The shield’s highest point is Pico da Neblina in Brazil, at 2,995 meters (9,826 feet). This peak is part of the larger Neblina massif, a heavily eroded sandstone plateau that straddles the Venezuela-Brazil border and has lost the typical tabletop shape of other tepuis in the region.

**Ecology** The Guiana Shield is one of the most biodiverse areas on Earth, with many species found nowhere else. It hosts over 3,000 vertebrate species: 1,168 freshwater fish, 269 amphibians (54% of which are endemic), 295 reptiles (29% endemic), 1,004 birds (7.7% endemic), and 282 mammals (11% endemic). Invertebrate diversity is largely unrecorded, but several endemic butterflies and dung beetles are known. Plant life is equally rich, with 13,367 species of vascular plants identified, about 40% of them endemic. The shield supports the largest expanse of tropical forest on any Precambrian shield in the world. This Guianan rain forest resembles Amazonian rain forest and includes protected areas such as the Iwokrama Forest, Kaieteur, and Kanuku National Park in Guyana; the Central Suriname Nature Reserve (a UNESCO World Heritage Site) in Suriname; the Guiana Amazonian Park in French Guiana; and the Tumucumaque National Park in Brazil’s Amapá state. In Venezuela, forests are protected by Canaima, Parima-Tapirapeco, and Serranía de la Neblina national parks. In 2014, Colombia designated a 250-hectare area of the Guiana Shield as a Ramsar Wetland, giving it international protected status under the Ramsar Convention. Recent research shows that while the Guiana Highlands’ ecosystems remain vibrant, emerging issues include the invasive plant *Poa annua* and the aggressive weed *Polypogon elongatus*, as well as the infectious fecal bacterium *Helicobacter pylori*.