Gabon is situated at the northwestern margin of the Congo Craton—a region of stable, ancient crust—and preserves very ancient rock units across 75% of the country, with overlying sedimentary units from the Cretaceous and other more recent periods.[1]
The oldest rocks in Gabon are granitoidArchean basement rocks, 2.8 to 2.6 Ga old, that span into Cameroon, Equatorial Guinea and the Republic of Congo. The basements rocks are divided between the Chaillu Massif and North Gabon Massif. Like many other Archean cratons, the granitoid rocks are associated with potassic rocks, granite, monzonite, syenite and diorite-tonalite-granodiorite sequences. A large charnockitic body—a series of metamorphic rocks with varying chemical composition—exists in southern Gabon. Unlike other parts of Africa, Gabon lacks greenstone belt development.
Proterozoic (2500-541 Ma)edit
The Francevillian biota is known as one of the oldest form of possible Eukaryote communities, and is dated at around 2.1 ga.[2]
The Franceville Supergroup is made up of approximately 2 Ga Paleoproterozoic rocks, located in the east-central part of the country. The Ogooue orogenic belt in west-central Gabon also dates to the Paleoproterozoic, made up of heavily deformed metasedimentary and metavolcanic rocks from a fold and thrust belt. In the southwest, the Mayombe-Nyanga terrane contains high-grade Paleoproterozoic basement rocks, the Lambarene migmatite belt, as well as Doussa Supergroup metasedimentary rocks. Granites appear after the tectonic activity ended and are 1.9 Ga. The Mayombe Supergroup, within the Mayombe-Nyanga terrane, along with Franceville dolerite dykes from 970 Ma are the only remnants of the Mesoproterozoic rocks. The Nyanga Basin and de-la-Noya in the western part of Gabon expose the Neoproterozoic West Congolian Supergroup, with deformed volcanic and sedimentary sequences, similar to others in southern Africa. A small carbonatite formation was deposited 669 Ma in the Lambarene region.
Cretaceous-Quaternary (145 million years ago to the present)edit
A horst from the Early Cretaceous splits the Lambarene-Chincoua basement rocks and divides the overlying western sedimentary basin in two. The eastern, interior basin is made of a mix of lacustrine and continental sedimentary rocks, while marine sediments are common in the western basin, from the Cretaceous to as recently as the Quaternary in the past 2.5 Ma.[3]
Gabon has the world's only site known to have self-sustaining natural nuclear fission, at the Oklo reactor zones near the town of Franceville in the Haut-Ogooué province. The site was discovered in 1972, during French mining for uranium to supply nuclear reactors. Geologists noticed an unusually low concentration of uranium-235, leading to the current theory that the site was a natural nuclear reactor two billion years ago. Although the original Oklo Mine's resources are now depleted, 17 other sites have been found in the same region that once sustained nuclear fission.
Half of the reactor zones lack carbonaceous material and in these locations, cesium, rubidium, strontium and boron escaped and were lost. However, in others uraninite is encased in solidified two billion year old bitumen. Some geologists have suggested that this natural bitumen encasement could be a way of storing human produced nuclear waste in permanent geologic disposal sites.[4]
Natural resource geologyedit
The petroleum sector is integral to the Gabonese economy. Oil and gas are produced from the western sedimentary basin, which extends into the Atlantic Ocean as far west as Sao Tome. Hydrocarbons formed in rift basins left over from the opening of the Atlantic Ocean. Many of the oil and gas deposits are contained within salt diapirs, better known as salt dome features. The Rabi-Kounga oil field, the country's largest, was discovered onshore in 1985, 100 kilometers north of Gamba. It began producing in 1989. Other oil and gas fields are likely to be discovered as drilling and seismic research continues. Manganese ore is mined in lower Proterozoic deposits near Mounana in southeast Gabon. Uranium deposits were mined out of sandstones in the Franceville Basin until 1999. Diamonds are commonplace in Gabon, mainly extracted in the Makongonio area in the south as well as the Mitzic region in the north. Other resources include iron ore in the Makokou-Mekambo area, barite near Dourekiki and phosphate and niobium at Mabounie. Geologists have identified other deposits such as tantalite, zinc, lead, dolomitic limestone, talc, potash and a variety of other materials.[5]
Referencesedit
^Schlüter, Thomas (2008). Geological Atlas of Africa. Springer. p. 110.
^El Albani, Abderrazak; Bengtson, Stefan; Canfield, Donald E.; Riboulleau, Armelle; Rollion Bard, Claire; Macchiarelli, Roberto; et al. (2014). "The 2.1 Ga Old Francevillian Biota: Biogenicity, Taphonomy and Biodiversity". PLOS ONE. 9 (6): e99438. Bibcode:2014PLoSO...999438E. doi:10.1371/journal.pone.0099438. PMC4070892. PMID 24963687.
geology, gabon, gabon, situated, northwestern, margin, congo, craton, region, stable, ancient, crust, preserves, very, ancient, rock, units, across, country, with, overlying, sedimentary, units, from, cretaceous, other, more, recent, periods, contents, stratig. Gabon is situated at the northwestern margin of the Congo Craton a region of stable ancient crust and preserves very ancient rock units across 75 of the country with overlying sedimentary units from the Cretaceous and other more recent periods 1 Contents 1 Stratigraphy amp Tectonics 1 1 Proterozoic 2500 541 Ma 1 2 Cretaceous Quaternary 145 million years ago to the present 2 Oklo natural nuclear fission reactor 3 Natural resource geology 4 ReferencesStratigraphy amp Tectonics editThe oldest rocks in Gabon are granitoid Archean basement rocks 2 8 to 2 6 Ga old that span into Cameroon Equatorial Guinea and the Republic of Congo The basements rocks are divided between the Chaillu Massif and North Gabon Massif Like many other Archean cratons the granitoid rocks are associated with potassic rocks granite monzonite syenite and diorite tonalite granodiorite sequences A large charnockitic body a series of metamorphic rocks with varying chemical composition exists in southern Gabon Unlike other parts of Africa Gabon lacks greenstone belt development Proterozoic 2500 541 Ma edit nbsp The Francevillian biota is known as one of the oldest form of possible Eukaryote communities and is dated at around 2 1 ga 2 The Franceville Supergroup is made up of approximately 2 Ga Paleoproterozoic rocks located in the east central part of the country The Ogooue orogenic belt in west central Gabon also dates to the Paleoproterozoic made up of heavily deformed metasedimentary and metavolcanic rocks from a fold and thrust belt In the southwest the Mayombe Nyanga terrane contains high grade Paleoproterozoic basement rocks the Lambarene migmatite belt as well as Doussa Supergroup metasedimentary rocks Granites appear after the tectonic activity ended and are 1 9 Ga The Mayombe Supergroup within the Mayombe Nyanga terrane along with Franceville dolerite dykes from 970 Ma are the only remnants of the Mesoproterozoic rocks The Nyanga Basin and de la Noya in the western part of Gabon expose the Neoproterozoic West Congolian Supergroup with deformed volcanic and sedimentary sequences similar to others in southern Africa A small carbonatite formation was deposited 669 Ma in the Lambarene region Cretaceous Quaternary 145 million years ago to the present edit A horst from the Early Cretaceous splits the Lambarene Chincoua basement rocks and divides the overlying western sedimentary basin in two The eastern interior basin is made of a mix of lacustrine and continental sedimentary rocks while marine sediments are common in the western basin from the Cretaceous to as recently as the Quaternary in the past 2 5 Ma 3 Oklo natural nuclear fission reactor editMain article Oklo Mine Gabon has the world s only site known to have self sustaining natural nuclear fission at the Oklo reactor zones near the town of Franceville in the Haut Ogooue province The site was discovered in 1972 during French mining for uranium to supply nuclear reactors Geologists noticed an unusually low concentration of uranium 235 leading to the current theory that the site was a natural nuclear reactor two billion years ago Although the original Oklo Mine s resources are now depleted 17 other sites have been found in the same region that once sustained nuclear fission Half of the reactor zones lack carbonaceous material and in these locations cesium rubidium strontium and boron escaped and were lost However in others uraninite is encased in solidified two billion year old bitumen Some geologists have suggested that this natural bitumen encasement could be a way of storing human produced nuclear waste in permanent geologic disposal sites 4 Natural resource geology editThe petroleum sector is integral to the Gabonese economy Oil and gas are produced from the western sedimentary basin which extends into the Atlantic Ocean as far west as Sao Tome Hydrocarbons formed in rift basins left over from the opening of the Atlantic Ocean Many of the oil and gas deposits are contained within salt diapirs better known as salt dome features The Rabi Kounga oil field the country s largest was discovered onshore in 1985 100 kilometers north of Gamba It began producing in 1989 Other oil and gas fields are likely to be discovered as drilling and seismic research continues Manganese ore is mined in lower Proterozoic deposits near Mounana in southeast Gabon Uranium deposits were mined out of sandstones in the Franceville Basin until 1999 Diamonds are commonplace in Gabon mainly extracted in the Makongonio area in the south as well as the Mitzic region in the north Other resources include iron ore in the Makokou Mekambo area barite near Dourekiki and phosphate and niobium at Mabounie Geologists have identified other deposits such as tantalite zinc lead dolomitic limestone talc potash and a variety of other materials 5 References edit Schluter Thomas 2008 Geological Atlas of Africa Springer p 110 El Albani Abderrazak Bengtson Stefan Canfield Donald E Riboulleau Armelle Rollion Bard Claire Macchiarelli Roberto et al 2014 The 2 1 Ga Old Francevillian Biota Biogenicity Taphonomy and Biodiversity PLOS ONE 9 6 e99438 Bibcode 2014PLoSO 999438E doi 10 1371 journal pone 0099438 PMC 4070892 PMID 24963687 Schluter 2008 pp 111 112 Mossman Gauthier Lafaye Dutkiewicz Bruning 2008 Carbonaceous substances in Oklo reactors Geological Society of America a href Template Cite news html title Template Cite news cite news a CS1 maint multiple names authors list link Schluter 2008 pp 112 113 nbsp Wikimedia Commons has media related to Geology of Gabon nbsp Geology portal Retrieved from https en wikipedia org w index php title Geology of Gabon amp oldid 1172948133, wikipedia, wiki, book, books, library,
