The Guiana Shield underlies Guyana (previously British Guiana), Suriname (previously Dutch Guiana) and French Guiana (or Guyane), most of 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 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 comglomerates presumed to be 1.8 to 1.4 Ga in age.
There are three upland areas 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). 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.
The Guiana Shield is one of the regions of highest biodiversity in the world, and has many endemic species. The region houses has 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.