The Francevillian B Formation, also known as the Francevillian Formation or FB2 in scientific research, is a

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

black shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especia ...

provinces close to the town of

Franceville Franceville is one of the four largest cities in Gabon, with a population of 110,568 at the 2013 census. It lies on the Mpassa River and at the end of the Trans-Gabon Railway and the N3 road. It grew from a village named Masuku when Pierre Savor ...

Gabon Gabon (; ; snq, Ngabu), officially the Gabonese Republic (french: République gabonaise), is a country on the west coast of Central Africa. Located on the equator, it is bordered by Equatorial Guinea to the northwest, Cameroon to the nort ...

. The formation was deposited between 2.14-2.08 Ga (billion years ago) in the

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 ...

, and is a unique shale among others from that time frame because (unlike other black shale provinces formed at that time) the ''Francevillian Formation'' has not experienced any thermal overprinting due to diagenesis after burial nor significant metamorphism since it was deposited. The ''Francevillian B Formation'' is important to the field of palaeontology because it contains fossil material of possible eukaryotic organisms from around 2.1 Ga which have been informally dubbed the "''

Francevillian biota The Francevillian biota (also known as Gabon macrofossils or Gabonionta) is a group of 2.1-billion-year-old Palaeoproterozoic, macroscopic organisms known from fossils found in Gabon in the Palaeoproterozoic Francevillian B Formation, a black shal ...

''" or "'' Gabonionta''". This biota takes on the appearance of a multitude of forms such as discs with ruffled rides, ruffled blobs, "stalked/tailed flowers" and strings of beads that were interpreted by Abderrazak El Albani as being akin to that of

Dictyostelium ''Dictyostelium'' is a genus of single- and multi-celled eukaryotic, phagotrophic bacterivores. Though they are Protista and in no way fungal, they traditionally are known as "slime molds". They are present in most terrestrial ecosystems ...

slime moulds Slime mold or slime mould is an informal name given to several kinds of unrelated eukaryotic organisms with a life cycle that includes a free-living single-celled stage and the formation of spores. Spores are often produced in macroscopic mu ...

. El Albani also described a multitude of "strings of beads" which appear to have been similar to those found on the "stalked flowers" that he described along with the other biota which have been compared to the Ediacarans ''

Beltanelloides ''Beltanelliformis'' is a genus of discoid fossil from the Ediacaran period containing the two species B. brunsae and B. minutae, sometimes ascribed to the Ediacaran Biota. The chemical signature obtained from organically preserved specimens po ...

'' and ''

Nemiana ''Beltanelliformis'' is a genus of discoid fossil from the Ediacaran period containing the two species B. brunsae and B. minutae, sometimes ascribed to the Ediacaran Biota. The chemical signature obtained from organically preserved specimens po ...

''. The fossils of the biota from the ''Francevillian B formation'' are assumed to have had primitive ''cell-to-cell'' communication, as they are older than the oldest known evidence for the existence of multicellularity in the fossil record

Significance and History

The ''Francevillian B. Formation'' was discovered by a team of palaeontologists led by the French-Moroccan palaeontologist Abderrazak El Albani in 2010 with assistance from the

University of Poitiers The University of Poitiers (UP; french: Université de Poitiers) is a public university located in Poitiers, France. It is a member of the Coimbra Group. It is multidisciplinary and contributes to making Poitiers the city with the highest studen ...

.Experiment Life – the Gabonionta
(Press Release). 4 March 2014. Naturhistorisches Museum Wien The team revolutionized ideas about the earliest life on Earth, because the earliest known geochemical evidence dates back as far as 3.7 Ga, and discovered a biota made of macroscopic multicellular organisms which were dated to be around 2.1 billion years old that were informally named the "

". However, these fossils had multiple interpretations and were at one time thought of as being

microbial mats A microbial mat is a multi-layered sheet of microorganisms, mainly bacteria and archaea, or bacteria alone. Microbial mats grow at interfaces between different types of material, mostly on submerged or moist surfaces, but a few survive in deserts. ...

similar to those found in the Ediacaran. A combination of scanning electron microscopy, petrographic analyses, Raman spectroscopy and analyses of the elements of the carbon-rich laminae and microtexure from the fossils concluded that the biota of the ''Francevillian B Formation'' were of organic origin. The

Franceville basin The Franceville Basin is a 1.6–2.1 billion year old sedimentary basis in Gabon. It contains unmetamorphosed sediments. It is notable for containing the Francevillian Biota, which is likely the oldest multicellular life known. A natural fission r ...

also has another basin near it, the Lastourville basin.

Sedimentology

The ''Francevillian Formation'' has recently been discovered to contain traces of

uranium Uranium is a chemical element with the 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 is weak ...

because it has been assumed that it contained and hosted natural nuclear reactors within it. 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 and migration and fluid mixing along with hydrofracturing are the cause of the uranium mineralization. During burial of the formation, its multiple black shales were heated and in doing so expelled

hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...

s that migrated into underlying

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

s, 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 Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...

. 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.

Biota

The ''Francevillian B formation'' is most notable for its significant fossil findings of the informally dubbed "Francevillian biota". These centimetre-sized discs include a wide variety of shapes, which include elongate, lobate and rod-shaped "strings of beads" that are often associated with one another and are ubiquitous to the formation. With the combination of Microtomography,

Geochemistry Geochemistry is the science that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems such as the Earth's crust and its oceans. The realm of geochemistry extends beyond the Earth, encompassing the ...

and analysing sediments has revealed that this biota fossilized in the early stages of

diagenesis Diagenesis () is the process that describes physical and chemical changes in sediments first caused by water-rock interactions, microbial activity, and compaction after their deposition. Increased pressure and temperature only start to play a ...

. A rise in Oxygen levels followed up with the emergence of this biota and is further evidence to support the idea of surface Oxygenation being able to evolutionary and ecology expansion of complex macro and megascopic life, with there also being the inclusion of organic-walled

Acritarch Acritarchs are organic microfossils, known from approximately 1800 million years ago to the present. The classification is a catch all term used to refer to any organic microfossils that cannot be assigned to other groups. Their diversity refle ...

s. The reports of these centimetre-sized pyritized fossils from

have opened a new window on the vision of the fossil record and also shows new evidence for the existence of some of the oldest known multi-cellular organisms in the fossil record. Grypania spiralis may have also been a Eukaryote from about 2 Billion years ago. ''Grypania'' and

Horodyskia ''Horodyskia'' is a fossilised organism found in rocks dated from to . Its shape has been described as a "string of beads" connected by a very fine thread. It is considered one of the oldest known eukaryotes. Biology Comparisons of differe ...

(although the latter is much younger than the former and younger than the Francevillian Biota) are also from a similar timeframe (similar as in appeared in a timeframe which is similar to the timeframe in which the Francevillian biota appeared) as the Francevillian biota, with ''Grypania'' being from around 2.0-2.1 GA and ''Horodyskia'' being dated to about 1.5-0.9 GA.

The Francevillian Biota and the Origin of life

Paleoproterozoic stromatolites Franceville

The

are, in part with some geochemical traces of organic matter from Western

Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland i ...

, part of the earth's earliest probable life forms and provided crucial steps in the evolution of Eukaryotes and various other organisms. However, the biota seen in the ''Francevillian Formation'' sparked some debating on their full taxonomic affinity, as well as the evolution and origin of organisms and modern-day Phyla. The interpretation of this biota as being colonies of Archaea (like ''Grypania'' and ''Horodyskia'') has not been accepted, however, because of their more complex morphology and general appearance the up-to fossils, with about 450 specimens from around 45 different horizons, are somewhat circular-blob-like in outline (this varies throughout each form) but others are elongate and more or else resemble

Flatworms The flatworms, flat worms, Platyhelminthes, or platyhelminths (from the Greek πλατύ, ''platy'', meaning "flat" and ἕλμινς (root: ἑλμινθ-), ''helminth-'', meaning "worm") are a phylum of relatively simple bilaterian, unsegment ...

. However, it's unknown if the various different forms of organisms from the ''Francevillian B Formation'' represent either a single species but in different stages of life/forms, or if they represent several individual species and taxa. These fossils have been analysed and reconstructed using computer software, and it revealed a common feature that all of the members of the Biota share in common; a spherical central element is present in all of them that was often flexible and exhibits a tiny amount of folds. However, it might've been caused because of a presumed gelatinous central element that is commonly surrounded by a fringe around its entirety deforming after death/preservation.

References

{{reflist, 30em

External links

* For more images of the Francevillian biota, se
Experiment Life – the Gabonionta (English version)
Geology of Gabon Shale formations Fossils of Gabon Gabon Paleontological sites Oil shale formations Geography of Gabon Precambrian fossils Life Prehistoric Africa by country Precambrian Africa