Guyana occurs within the northern part of the
Guiana Shield
The Guiana Shield (french: Plateau des Guyanes, Bouclier guyanais; nl, Hoogland van Guyana, Guianaschild; pt, Planalto das Guianas, Escudo das Guianas; es, Escudo guayanés) is one of the three cratons of the South American Plate. It is a ...
. The Guiana Shield forms the northern part of the
Amazonian Craton
The Amazonian Craton is a geologic province located in South America. It occupies a large portion of the central, north and eastern part of the continent and represents one of Earth's largest cratonic regions. The Guiana Shield and Central Braz ...
, the core of the South American continent.
Most of the geology of northern Guyana consists of
Palaeoproterozoic
The Paleoproterozoic Era (;, also spelled Palaeoproterozoic), spanning the time period from (2.5–1.6 Ga), is the first of the three sub-divisions ( eras) of the Proterozoic Eon. The Paleoproterozoic is also the longest era of the Earth's ...
Orosirian
The Orosirian Period (; grc, ὀροσειρά, translit=oroseirá, meaning "mountain range") is the third geologic period in the Paleoproterozoic era (geology), Era and lasted from annum, Mya to Mya (million years ago). Instead of being based ...
greenstone belts (Barama-Mazaruni Supergroup) intruded by granites. These are overlain unconformably by the
Statherian
The Statherian Period (; grc, σταθερός, statherós, meaning "stable, firm") is the final geologic period in the Paleoproterozoic Era and lasted from Mya to Mya (million years ago). Instead of being based on stratigraphy, these dates ar ...
Burro-Burro Group, which consist of the Muruwa Formation sandstones and Iwokrama Formation felsic volcanics. Both are intruded by granites associated with the Iwokrama Formation. Some folding occurred before these were overlain by the locally unconformable almost flat lying Roraima Group.
[Gibbs, A.K & Barron, C.N (1993). ''The Geology of the Guiana Shield''. Oxford University Press.]
Major mafic sills and dykes of the Avanavero Suite intrude all of the older rocks, and are part of a
Large Igneous Province
A large igneous province (LIP) is an extremely large accumulation of igneous rocks, including intrusive (sills, dikes) and extrusive (lava flows, tephra deposits), arising when magma travels through the crust towards the surface. The formation ...
(LIP). Numerous mafic dykes intruded the basement in the
late Permian
Late may refer to:
* LATE, an acronym which could stand for:
** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia
** Local-authority trading enterprise, a New Zealand business law
** Local average treatment effect, ...
and Early Jurassic, associated with the start of the separation of Africa from South America. These are part of the
Central Atlantic Magmatic Province
The Central Atlantic magmatic province (CAMP) is the Earth's largest continental large igneous province, covering an area of roughly 11 million km2. It is composed mainly of basalt that formed before Pangaea broke up in the Mesozoic Era, near the ...
(CAMP).
The northern Guiana Shield, including Guyana is separated from Southern Guiana Shield by ENE to NE trending Tumbes /Guayaquil - Tacutu Tectonic Lineament. This is a major regional pre-Cambrian shear zone / mega-shear which is believed to have been re-activated several times. At the beginning of the Mesozoic when Africa and South America started to separate this re-activated again and was involved in formation of the Takutu Graben in the lower
Rupununi
The Rupununi is a region in the south-west of Guyana, bordering the Brazilian Amazon. The Rupununi river, also known by the local indigenous peoples as ''Raponani'', flows through the Rupununi region. The name Rupununi originates from the word '' ...
area and the Guyana-Suriname basin near the coast and offshore. Both these sedimentary basins have
oil potential, and in 2015 significant oil was found in a deep water area off Guyana. During the Mesozoic the headwaters of the
Upper Orinoco and
Rio Branco flowed through the Takutu Graben via the Essequibo either to the current river mouth, to the Corentyne, the Berbice or the Canje Rivers.
Tilting associated with rifting of the Atlantic Ocean resulted in complex patterns of river capture, so now the headwaters of the Rio Branco flow to the south via the Amazon, and the headwaters of the Upper Orinoco flow to the west and north. Water and sediment volumes directly flowing east are now much reduced.
References
{{South America topic, Geology of