8 junio, 2024

Geological history of Venezuela: eras and formations

The geological history of Venezuela It began 4.6 billion years ago, when the first igneous and metamorphic rocks were formed, giving rise to the Guyana region.

The Venezuelan territory began its formation during the time in which the South American continent began to separate from the African continent, giving space to the Atlantic Ocean.

The geologists agreed to identify large groups that allowed an idea of ​​the evolution of the geographic forms of Venezuela. Thus four eras were determined: Precambrian, Paleozoic, Mesozoic and Cenozoic. These, in turn, were fragmenting in different periods.

The geological history of Venezuela includes the evolution of the Guiana shield and the final part of the great Andean mountain system, made up of the Andes mountain range and the Coastal mountain range. These were the main geographical accidents from which other minor ones were generated.

In the first place, the Guayanés massif was formed, in the south of the country, where important mountain ranges arose. Later, in the north, the Andes mountain system arose.

In the valley that currently joins them, there was only water; Thus, for a time the Venezuelan territory was reduced to two islands.

With the growth and transformation of the mountains, various sediments reached the lake that separated the two islands, filling it up and generating the great valley known as the Venezuelan plains.

The geological eras in Venezuela

In the geological history of Venezuela, as in that of the world, four eras are identified that account for the formation and transformation of its relief: Precambrian, Paleozoic, Mesozoic and Cenozoic.

precambrian era

The Precambrian era began 4.6 billion years ago and dates back to 570 million years ago.

During this period, the basal complex typical of the Venezuelan Guayana, in the south of the country, was created; also in the Andes; in the northern mountain range of Perijá, Zulia state; and in El Baúl, state of Cojedes.

paleozoic era

This era lasted 325 years and is counted from 570 to 245 million years ago in the history of geology.

During this era the primitive Andes arose, to the northwest of the country; initially there was a kind of elevation of the mountains and, later, a wear. Currently there are reliefs that still belong to this era.

The tectonic plate, called South American, moved slightly to the west. And the plate known as the Caribbean moved to the east, raising the territory in the form of mountain ranges.

Mesozoic era

During the Mesozoic era, the Coastal Range was formed, and it developed from 245 to 65 million years ago.

In this era, from the Caribbean Sea emerged what is now known as the mountain system, which surrounds the northwest coast of Venezuela.

Cenozoic era

The Cenozoic era has developed from 65 million years ago to the present day.

It was in this period when the Andes that we know today finished forming and, after the sedimentation that this formation left behind, the oil deposits were deposited in the state of Zulia and to the east.

In addition, the delta of the Orinoco River was expanded, and the basin of Lake Maracaibo sank giving way to new mountains.

The main Venezuelan geological formations

1- Guyanese shield

The Guyanese shield is one of the oldest geological zones on the planet and occupies Venezuelan, Colombian and Brazilian territory; It is estimated that it is 3,500 years old.

The transposition of two tectonic layers —the South American and the Caribbean— raised the territory that was under the sea and created a set of mountains and mountain ranges, which make up the Guayana region in Venezuela.

The oldest rocks in Venezuela are found in this site and it is known as the “Basal Complex”. It is formed mainly by igneous rocks, among which is granite.

1,500 million years ago, a sedimentary cover was deposited in the Guayana region, made up of sandstone for the most part, giving rise to the plateaus known as tepuis.

The same erosion process created a large sand deposit on the banks of the Orinoco River, generating the largest dune area in the country, in the state of Apure.

This area is currently known as the Santos Luzardo National Park and there the dunes or sand dunes coexist with mighty rivers and savannah vegetation.

Among the main formations of the Guyanese shield are that of El Callao, located in the vicinity of the Yuruari River and with volcanic formations.

It is also possible to find the formation on the Cicapra ravine, formed by stones known as amphibole, interspersed by volcanic breaks.

There are also the formations of Yuruari, Caballape, Cuchivero and Roraima.

2- Andes Mountains

After the Táchira depression, and after the continuation of the Andes mountain range to the northeast, is the Mérida mountain range, which extends to the Barquisimeto and Carora depression.

The western chain of the mountain system is made up of the Sierra de Perijá, which rises to 3,750 meters, and the eastern chain that forms the Mérida mountain range and culminates in Pico Bolívar, at 4,978 meters.

The two mountain ranges enclose the depression of Lake Maracaibo, with 13,280 km².

Among the most outstanding formations are that of Bella Vista; Caparo, with some fossiliferous slates; and the Mucuchachí formation, made up mainly of gray to brown slates, sometimes carbonaceous, silty and containing fossils and pyrites.

The Sabaneta formation also stands out, consisting mainly of yellow, gray, purple-red and brown sandstones. In addition, there is the Palmarito formation, in the south of the state of Mérida, and the La Quinta formation.

3- The plains

The Venezuelan plains occupy 35% of the national territory and were formed thanks to the sedimentation suffered by a large lake that separated the Guayana region and the Andes and Coastal ranges.

This region also includes the plain of the Orinoco river delta, whose characteristics are very similar to those of the plains region.

References

Mencher E. et al. (1953) Geology of Venezuela and Its Oil Fields. Bulletin of the American Association Petroleum Geologists. See 37 No. 4.pp:690-777
McNab JG et al. (1952). Evolution of Petroleum. Industrial and Engineering Chemistry. 44 (11), pp: 2556–2563
Macqueen, RW, & Leckie, DA (1992). Foreland basins and fold belts. United States: Tulsa, OK (United States); American Association of Petroleum Geologists.

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