Caribbean geology, distributed over many different countries and islands, appears to be complex. Documentation ranges from good, in highly explored, contiguous areas in northern South America, to poor or absent in remote areas of tropical vegetation cover and weathering. There are no recognised oceanic spreading anomalies or fractures to indicate the age or tectonic origin of Caribbean plate crust. The only spreading ridge in the whole of Middle America lies in the centre of the Cayman Trough, which is a large, plate-boundary pull-apart.
Geophysical investigations show that parts of the Caribbean plate are much thicker than normal oceanic crust and have a different seismic velocity structure (Officer et al., 1957). This thick crust is described as an oceanic plateau (Donnelly, 1973). The "original" plateau (rhomboid area in Figure 1) was a 20-km-thick area in the western part of the Venezuela Basin. Over time this has become linked to similar crust in the Colombia Basin and oceanic crust accreted around the plate margins. The assemblage is regarded as the best exposed oceanic plateau in the world (Kerr et al., 1997).
Geology of southeastern Venezuela
The Roraima formation of conglomerates, sandstones, and shales, with interbedded thin tuffs, outcrops in the Gran Sabana in southeastern Venezuela. Its greatest thickness, 2400 meters, represents merely an erosion remnant. Thick dikes, sills, and laccoliths intrude it as well as a few acid dikes probably related to the same magma. Its sediments are highly silicified. Its age is undetermined. It was deposited on the peneplaned surface of the Archean basement of the Guayana shield. The Roraima beds are essentially horizontal. The present topography of mesas and cuestas is controlled by an original northward dip of the sediments off the old basement combined with the structures resulting from intrusions. The drainage is controlled by stream piracy due to a gentle southward tilting of the older northward-dipping beds. Gold and diamonds are found in small quantities.
Geology of central Aragua
The Villa de Cura group, 3,000 meters of Cretaceous metamorphosed volcanics, underlies most of the central Argua area, located on the southern flank of the mountains in north-central Venezuela. It consists of four conformable formations--El Cano, El Chino, and El Carmen (all metamorphosed spilitic basalts, now greenstones) and Santa Isabel (uppermost), a more siliceous formation of schists and granulites, frequently with glaucophane. North of the Villa de Cura group, the phyllites, sandstones, conglomerates, and distinctive limestone of the Tucutunemo formation, uppermost member of the Caracas group, crop out. An early Cretaceous age is suggested for the Caracas group. Deformation and metamorphism occurred in the mid-Cretaceous, followed by extrusion of spilitic basalts and tuffs of the Tiara formation. During Maestrichtian to Paleocene time, siltstones, sandstones, and foraminiferal limestones of the Paracotos formation were deposited.
Geology of Guyana in Venezuela
Skirting the Orinoco are the Llanos; these, as elsewhere, are characterized by a growth of coarse grass, Cyperacæ, and shrubby trees, the chief of which, and often the only species, is the chaparro (Curtella Americana); the soil is of the poorest description, being a loose sand, highly absorbent and of great heat-radiating power. At the distance of fifteen miles or so from the river, the land rises into scarped, low, more or less wooded heights, constituting the serranos, interspersed with grassy slopes and plains. These serranos by easy gradations lead us on to the range of the Itacama Mountains, which trend east and west and attain an elevation of about 3000 feet. The range occupies a breadth of about sixty miles ; and its southern slope is bounded by an undulating grassy.
Geology of Venezuela Tepui
The entire Guyana Shield consists of rock of igneous and metamorphic types, especially granites and gneisses, some of which were formed 3.6 billion years ago. These are some of the oldest rocks in the earth's crust, and formed the western section of the ancient supercontinent of Gondwana, which beganto break up in the late Jurassic (150 million years ago), as the Atlantic Ocean divided the South American and African land blocks. Most of the base rock was later covered by layer upon layer of sand, probably from adjacent uplands areas of Gondwana. These layers were heavily compressed and cemented together by silica during successive thermal events and reached a thickness of several thousands metres - the quartzite and sandstone rocks known today as the Roraima Formation.