Guyana occurs within the northern part of the Guiana Shield. The Guiana Shield forms the northern part of the Amazonian Craton, the core of the South American continent.

Most of the geology of northern Guyana consists of Palaeoproterozoic Orosirian greenstone belts (Barama-Mazaruni Supergroup) intruded by granites. These are overlain unconformably by the Statherian 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.[1]

Major mafic sills and dykes of the Avanavero Suite intrude all of the older rocks, and are part of a Large Igneous Province (LIP).[2] Numerous mafic dykes intruded the basement in the late Permian and Early Jurassic, associated with the start of the separation of Africa from South America. These are part of the Central Atlantic Magmatic Province (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.[3][4] 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[5] in the lower Rupununi 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.[1][6] 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

  1. ^ a b Gibbs, A.K & Barron, C.N (1993). The Geology of the Guiana Shield. Oxford University Press.
  2. ^ Reis, Nelson Joaquim; Teixeira, Wilson; Hamilton, Mike A.; Bispo-Santos, Franklin; Almeida, Marcelo Esteves; d'Agrella-Filho, Manoel Souza (2013-08-01). "Avanavero mafic magmatism, a late Paleoproterozoic LIP in the Guiana Shield, Amazonian Craton: U–Pb ID-TIMS baddeleyite, geochemical and paleomagnetic evidence". Lithos. 174: 175–195. Bibcode:2013Litho.174..175R. doi:10.1016/j.lithos.2012.10.014. ISSN 0024-4937.
  3. ^ Jacques, JohnM (2003-09-01). "A tectonostratigraphic synthesis of the Sub-Andean basins: inferences on the position of South American intraplate accommodation zones and their control on South Atlantic opening". Journal of the Geological Society. 160 (5): 703–717. Bibcode:2003JGSoc.160..703J. doi:10.1144/0016-764902-089. ISSN 0016-7649. S2CID 140541642.
  4. ^ Klein, G.F., Zúñiga y Rivero, F.J., Hay-Roe, H. & Alvarez-Calderon (2011). "A Reappraisal of the Mesozoic/Cenozoic Tectonics and Sedimentary Basins of Peru" (PDF).((cite web)): CS1 maint: multiple names: authors list (link)
  5. ^ D. Crawford, F; E. Szelewski, C; D. Alvey, G (1985-01-01). "Geology and Exploration in the Takutu Graben of Guyana Brazil". Journal of Petroleum Geology. 8 (1): 5–36. Bibcode:1985JPetG...8....5C. doi:10.1111/j.1747-5457.1985.tb00189.x.
  6. ^ Armbruster, J.W, Lujan, N. & de Souza, L. (2017). "The Proto-Berbice, an Ancient River that Influences the Modern Distributions and Conservation Challenges of Freshwater Fishes throughout the Western Guiana Shield" (PDF).((cite web)): CS1 maint: multiple names: authors list (link)
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