Francevillian B Formation | |
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Stratigraphic range: Palaeoproterozoic (Rhyacian) | |
Type | Geological formation |
Unit of | Francevillian Basin |
Area | 25,000 square kilometers (9,700 sq mi) |
Lithology | |
Primary | Black Shale |
Location | |
Region | East-central Gabon |
Country | Gabon |
Extent | 35,000 kilometers (22,000 mi) |
Type section | |
Named for | Franceville, a nearby town |
Named by | Abderrazak El Albani |
Map of the Geology of the Franceville basin |
Part of a series on |
The Francevillian basin |
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The Francevillian B Formation, also known as the Francevillian Formation or FB2 in scientific research, is a geologic formation of black shale provinces close to the town of Franceville, Gabon from where it gets its name from. The formation was deposited between 2.14-2.08 Ga (billion years ago) in the Palaeoproterozoic, [1] and, uniquely, has not experienced any thermal overprinting due to diagenesis after burial nor significant metamorphism since it was deposited, unlike other formations deposited around the same time. [2] The formation contains possible fossils, including the macroscopic "Francevillian Biota", which has been suggested by some authors to represent the oldest known multicellular organisms, [3] [4] though other authors have questioned the supposed biological origin of the structures, and have suggested that they may instead be inorganic, such as artifacts of diagenesis. [5] [6]
The Francevillian Formation has recently been discovered to contain traces of uranium. The Francevillian basin itself already contained Oklo Mine, a natural nuclear reactor. [7] [8] [9] [10] However, the formation also witnessed a former system of petroleum which showed major amounts of uranium associated with organic matter. Several episodes of oil generation, migration and fluid mixing along with hydrofracturing are the cause of the uranium mineralization. [10] During burial of the formation, its multiple black shales were heated and in doing so expelled hydrocarbons that migrated into underlying sandstones, with the first episode of the oil migration being synchronous along with a silicification event that derived into a hot and low salinity fluid which is proven by fluid inclusions trapped in overgrowths of quartz. [10] However, the second episode of the oil migration was contemporaneous and has quartz dissolution with the episode being characterized by the mixing of hydrocarbons and oxidizing the uranium-bearing brine which in turn caused the precipitation of UO2 to be included in the oils. In the third and final episode of oil migration within the Francevillian B formation, oil-to-gas conversion generated overly-pressured gas trapped with uraniferous bitumen nodules in pores. Changes in the stress regime probably favoured radial hydrofracturing around the bitumen nodules as well as the subsequent development of a somewhat pervasive micro-fracture network. [10]
The formation has been proposed to have preserved microfossils, [11] as well as flattened disk-like macrofossils, the latter dubbed the "Francevillian biota". The initial discovers have claimed that the large structures claimed to be fossils are the oldest known multicellular organisms and eukaryotes, [3] [4] while other authors are more skeptical, suggesting that they may be of inorganic origin, such as an artifact of diagenesis. [5] [6]
The Ediacaran period is a geological period of the Neoproterozoic era that spans 96 million years from the end of the Cryogenian period at 635 Mya, to the beginning of the Cambrian period at 538.8 Mya. It is the last period of the Proterozoic eon as well as the last of the so-called "Precambrian supereon", before the beginning of the subsequent Cambrian period marks the start of the Phanerozoic eon where recognizable fossil evidence of life becomes common.
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Uranium is a chemical element; it has symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium radioactively decays by emitting an alpha particle. The half-life of this decay varies between 159,200 and 4.5 billion years for different isotopes, making them useful for dating the age of the Earth. The most common isotopes in natural uranium are uranium-238 and uranium-235. Uranium has the highest atomic weight of the primordially occurring elements. Its density is about 70% higher than that of lead and slightly lower than that of gold or tungsten. It occurs naturally in low concentrations of a few parts per million in soil, rock and water, and is commercially extracted from uranium-bearing minerals such as uraninite.
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The Paleoproterozoic Era is the first of the three sub-divisions (eras) of the Proterozoic eon, and also the longest era of the Earth's geological history, spanning from 2,500 to 1,600 million years ago (2.5–1.6 Ga). It is further subdivided into four geologic periods, namely the Siderian, Rhyacian, Orosirian and Statherian.
Oklo is a region near the town of Franceville, in the Haut-Ogooué province of the Central African country of Gabon. Several natural nuclear fission reactors were discovered in the uranium mines in the region in 1972.
A natural nuclear fission reactor is a uranium deposit where self-sustaining nuclear chain reactions occur. The conditions under which a natural nuclear reactor could exist were predicted in 1956 by Paul Kuroda. The remnants of an extinct or fossil nuclear fission reactor, where self-sustaining nuclear reactions have occurred in the past, are verified by analysis of isotope ratios of uranium and of the fission products. This was first discovered in 1972 in Oklo, Gabon by Francis Perrin under conditions very similar to Kuroda's predictions.
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The Gunflint chert is a sequence of banded iron formation rocks that are exposed in the Gunflint Range of northern Minnesota and northwestern Ontario along the north shore of Lake Superior. The Gunflint Chert is of paleontological significance, as it contains evidence of microbial life from the Paleoproterozoic. The Gunflint Chert is composed of biogenic stromatolites. At the time of its discovery in the 1950s, it was the earliest form of life discovered and described in scientific literature, as well as the earliest evidence for photosynthesis. The black layers in the sequence contain microfossils that are 1.9 to 2.3 billion years in age. Stromatolite colonies of cyanobacteria that have converted to jasper are found in Ontario. The banded ironstone formation consists of alternating strata of iron oxide-rich layers interbedded with silica-rich zones. The iron oxides are typically hematite or magnetite with ilmenite, while the silicates are predominantly cryptocrystalline quartz as chert or jasper, along with some minor silicate minerals.
The galactic year, also known as a cosmic year, is the duration of time required for the Sun to orbit once around the center of the Milky Way Galaxy. One galactic year is approximately 225 million Earth years. The Solar System is traveling at an average speed of 230 km/s (828,000 km/h) or 143 mi/s (514,000 mph) within its trajectory around the Galactic Center, a speed at which an object could circumnavigate the Earth's equator in 2 minutes and 54 seconds; that speed corresponds to approximately 1/1300 of the speed of light.
The Ediacaranbiota is a taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period. These were enigmatic tubular and frond-shaped, mostly sessile, organisms. Trace fossils of these organisms have been found worldwide, and represent the earliest known complex multicellular organisms. The term "Ediacara biota" has received criticism from some scientists due to its alleged inconsistency, arbitrary exclusion of certain fossils, and inability to be precisely defined.
Whether nuclear power should be considered a form of renewable energy is an ongoing subject of debate. Statutory definitions of renewable energy usually exclude many present nuclear energy technologies, with the notable exception of the state of Utah. Dictionary-sourced definitions of renewable energy technologies often omit or explicitly exclude mention of nuclear energy sources, with an exception made for the natural nuclear decay heat generated within the Earth.
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Abderrazak El Albani is a French-Moroccan sedimentologist, professor at University of Poitiers at the Hydrasa laboratory. He is known for describing the "Francevillian Biota" from the Paleoproterozoic of Gabon, which he suggests represents the oldest known multicellular organisms, though this claim has been questioned by other authors.
The Francevillian biota are a collection of 2.1-billion-year-old Palaeoproterozoic macroscopic structures, controversially suggested to be fossils, known from the Francevillian B Formation in Gabon, a black shale province notable for its lack of any noticeable metamorphism. The structures have been postulated by some authors to be evidence of the earliest form of multicellular life, and of eukaryotes. They were discovered by an international team led by Moroccan-French geologist Abderrazak El Albani, of the University of Poitiers, France. While they have yet to be assigned to a formal taxonomic position, they have been informally and collectively referred to as the "Gabonionta", including by the Natural History Museum Vienna in 2014. The status of the structures as fossils has been questioned.
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.
The Franceville Basin is a 1.6–2.1 billion year old sedimentary basin in Gabon. It contains unmetamorphosed sediments. It is notable for containing the Francevillian Biota, which are possibly the oldest multicellular life known. A natural fission reactor formed there about 1.8 - 2.1 billion years ago.
The identity of the [Francevillian biota] macrostructures remains unknown and their biogenicity is questionable