Early Eocene
In the geologic timescale the Ypresian is the oldest age or lowest stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by the Eocene Lutetian Age. The Ypresian i ...
marl
Marl is an earthy material rich in carbonate minerals, clays, and silt. When hardened into rock, this becomes marlstone. It is formed in marine or freshwater environments, often through the activities of algae.
Marl makes up the lower part o ...
s and
lignite
Lignite, often referred to as brown coal, is a soft, brown, combustible, sedimentary rock formed from naturally compressed peat. It has a carbon content around 25–35%, and is considered the lowest rank of coal due to its relatively low heat ...
Precambrian
The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...
basement
A basement or cellar is one or more floors of a building that are completely or partly below the ground floor. It generally is used as a utility space for a building, where such items as the furnace, water heater, breaker panel or fuse box, ...
and is overlain by Early Eocene basalts and Late Eocene to Early Oligocene conglomerates.
The up to thick formation has provided many fossil
mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
s of various groups among which the marsupials and related metatherians dominate, birds, snakes,
crocodile
Crocodiles (family (biology), family Crocodylidae) or true crocodiles are large semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term crocodile is sometimes used even more loosely to inclu ...
s,
amphibian
Amphibians are tetrapod, four-limbed and ectothermic vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terres ...
s, and several species of
gastropod
The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda ().
This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...
Tupi Tupi may refer to:
* Tupi people of Brazil
* Tupi or Tupian languages, spoken in South America
** Tupi language, an extinct Tupian language spoken by the Tupi people
* Tupi oil field off the coast of Brazil
* Tupi Paulista, a Brazilian municipalit ...
origin, and has two possible etymologies:
* "River of beautiful stones", a combination of the words ''itá'' (stone), ''porã'' (beautiful) and ''y'' (river)Bragança Júnior, 1992
* "River of brilliant stones", derived from the words ''itá'' (stone), ''berab'' (brilliant) and ''y'' (river)Carvalho, 1987, p.47
Description
The Itaboraí Formation is restricted to the Itaboraí Basin, a minibasin stretching across an area of of , in the vicinity of Itaboraí northeast of Rio de Janeiro, southeastern Brazil.Riccomini et al., 2004, p.390 Between 1933 and 1984, a local cement company exploited the rocks in the area and their workers discovered the first fossil remains in the formation.Santos & Carvalho, 2012, p.332 The now abandoned and largely inaccessible limestone quarries of this locality have yielded a diverse mammalian fauna from early late Paleocene fissure fillings. The sediments of the formation were described by Leinz in 1938.Riccomini, 1990, p.68 Presently, the basin is filled up with water impeding any collecting activity.Kellner & Campos, 1999, p.246
Basin history
The small basin, a small
half-graben
A half-graben is a geological structure bounded by a fault along one side of its boundaries, unlike a full graben where a depressed block of land is bordered by parallel faults.
Rift and fault structure
A rift is a region where the lithosphere ...
, is the oldestRiccomini et al., 2004, p.384 and smallestOliveira & Goin, 2011, p.107 of several
Cenozoic
The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...
The Itaboraí Formation rests unconformably on top of the
Precambrian
The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...
Paraíba do Sul Group, part of the Meso- to NeoproterozoicParaíba do Sul Complex.Torres Tiago, 2017, p.25 The Paleogene succession of the minibasin reaches a thickness of and consists of three depositional sequences, with the Itaboraí Formation representing the first two;Torres Tiago, 2017, p.26
* Sequence 1 (S1) - clastic limestones with travertine, grey carbonates and oolitic limestones, carbonatic
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, especial ...
s and
lignite
Lignite, often referred to as brown coal, is a soft, brown, combustible, sedimentary rock formed from naturally compressed peat. It has a carbon content around 25–35%, and is considered the lowest rank of coal due to its relatively low heat ...
s, deposited in a lacustrineenvironment, originating from debris flows in a tectonic lake. From this sequence gastropods are abundant, while woods, reptiles and mammals are scarce.
* Sequence 2 (S2) - carbonates filling caverns and dissolution cracks on a
karst
Karst is a topography formed from the dissolution of soluble rocks such as limestone, dolomite, and gypsum. It is characterized by underground drainage systems with sinkholes and caves. It has also been documented for more weathering-resistant ro ...
ic surface of Sequence 1, comprising fossiliferous
marl
Marl is an earthy material rich in carbonate minerals, clays, and silt. When hardened into rock, this becomes marlstone. It is formed in marine or freshwater environments, often through the activities of algae.
Marl makes up the lower part o ...
s, deposited in an alluvial to lacustrine environment, transported into these cavities by heavy rains and gravitational flows
* Sequence 3 (S3) - terrestrial siliciclastic sediments, including
mudstone
Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...
Early Eocene
In the geologic timescale the Ypresian is the oldest age or lowest stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by the Eocene Lutetian Age. The Ypresian i ...
.Torres Tiago, 2017, p.27
Thin section analysis suggests the travertine sequence went through a series of diagenetic processes: firstly, the deposition of the primary carbonate, followed by a set of percolating
iron oxide
Iron oxides are chemical compounds composed of iron and oxygen. Several iron oxides are recognized. All are black magnetic solids. Often they are non-stoichiometric. Oxyhydroxides are a related class of compounds, perhaps the best known of whic ...
enriched fluids and lastly a set of silica-rich fluids leading to the silica chalcedony and micro-crystalline deposition.Valente et al., 2017, p.227
Age
The Itaboraí Formation, defining the Itaboraian SALMA, was first thought to be early to mid Paleocene in age, until dating performed by Woodburne et al. in 2014 suggested as a more probable early Eocene age (53–50 Ma),Oliveira et al., 2016, p.2Woodburne et al., 2014, p.116 spanning polarity chron 23.Woodburne et al., 2014, p.112 The overlying basalts have been dated to the Early Eocene (52.6 ± 2.4 Ma). Another very important source of data is palynological analysis of a coal-bearing horizon (lignite) interlayered with alluvial fan deposits at the northern border of the Itaboraí Basin, suggesting a Paleocene to Eocene age.Oliveira & Goin, 2011, p.109 During this time, a biogeographical connection existed with Antarctica and, though separated by the developing South Atlantic, with Africa.Ezcurra & Agnolín, 2012, p.560 The deposits of the formation were formed during the
Early Eocene Climatic Optimum
Early may refer to:
History
* The beginning or oldest part of a defined historical period, as opposed to middle or late periods, e.g.:
** Early Christianity
** Early modern Europe
Places in the United States
* Early, Iowa
* Early, Texas
* Early ...
The Itaboraí Formation is the richest and one of few formations in Brazil providing Paleogene mammal faunas, between the older TiupampanMaria Farinha Formation of the
Parnaíba Basin
The Parnaíba Basin (Portuguese: ''Bacia do Parnaíba'') is a large cratonic sedimentary basin located in the North and Northeast portion of Brazil
Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the ...
Curitiba Basin
Curitiba () is the capital and largest city in the state of Paraná in Brazil. The city's population was 1,948,626 , making it the eighth most populous city in Brazil and the largest in Brazil's South Region. The Curitiba Metropolitan area c ...
Deseadan The Deseadan ( es, Deseadense) age is a period of geologic time (29.0–21.0 Ma) within the Oligocene epoch of the Paleogene to the Early Miocene epoch of the Neogene, used more specifically within the SALMA classification of South America. It fo ...
Tremembé Formation of the Taubaté Basin.Sedor, 2017, p.39
Despite its relatively small size, the São José de Itaboraí Basin comprises a diversified fossil assemblage. Among the groups found there, fossil birds are very rare, mainly due to their pneumatized bones. Only three bird species have been described up to this moment from the Itaboraí Basin. ''
Diogenornis fragilis
''Diogenornis'' is an extinct genus of ratites, that lived during the Early Eocene (Itaboraian to Casamayoran in the SALMA classification).marsupials and related metatherians. The species '' Lamegoia conodonta'' is the largest " condylarth" at Itaboraí and approximates the size of a wolf. '' Ricardocifellia protocenica'', originally described as ''Paulacoutoia protocenica'', is the smallest of the "condylarth" species of Itaboraí, but the most abundant.Bergqvist, 2008, p.107 The most abundant litoptern found in the formation is '' Protolipterna ellipsodontoides''.Bergqvist, 2008, p.108
Sequence 1 of the formation has provided many
land snail
A land snail is any of the numerous species of snail that live on land, as opposed to the sea snails and freshwater snails. ''Land snail'' is the common name for terrestrial gastropod mollusks that have shells (those without shells are known as ...
s, among which several new species. The records of Itaboraí are the oldest for the genera '' Austrodiscus'', ''
Brachypodella
''Brachypodella'' is a genus of gastropods belonging to the family Urocoptidae.
The species of this genus are found in Northern and Central America.
Species
Species:
*''Brachypodella antiperversa''
*''Brachypodella bourguignatiana''
*''Br ...
'', ''
Bulimulus
''Bulimulus'' is a genus of small to medium-sized tropical or sub-tropical, air-breathing land snails, pulmonate gastropod mollusks in the subfamily Bulimulinae within the family Bulimulidae.Breure A. S. H. & Romero P. (2012). "Support and su ...
'', ''
Cecilioides
''Cecilioides'' is a genus of very small, air-breathing land snails, terrestrial pulmonate gastropod mollusks in the family Ferussaciidae. MolluscaBase eds. (2020). MolluscaBase. Cecilioides A. Férussac, 1814. Accessed through: World Register ...
Eoborus
''Eoborus'' is a fossil genus of medium-sized air-breathing land snails, terrestrial pulmonate gastropods in the family Strophocheilidae. ''Eoborus'' is the oldest fossil record of Strophocheilidae, dating from the Middle Paleocene of Brazil ( ...
Leiostracus
''Leiostracus'' is a genus of small to medium-sized neotropical, air-breathing land snails, pulmonate gastropod mollusks in family Simpulopsidae.MolluscaBase eds. (2020). MolluscaBase. Leiostracus Albers, 1850. Accessed through: World Register of ...
'', ''
Plagiodontes
''Plagiodontes'' is a recent genus of small to medium-sized air-breathing land snails, terrestrial pulmonate gastropods in the family Odontostomidae.Breure A. S. H. & Romero P. (2012). "Support and surprises: molecular phylogeny of the land snail ...
Ferussaciidae
Ferussaciidae is a family of air-breathing land snails, terrestrial pulmonate gastropod mollusks in the superfamily Achatinoidea. MolluscaBase eds. (2020). MolluscaBase. Ferussaciidae Bourguignat, 1883. Accessed through: World Register of Marine ...
and
Strophocheilidae
Strophocheilidae is a taxonomic family of air-breathing land snails, terrestrial pulmonate gastropod mollusks in the superfamily Acavoidea (according to the taxonomy of the Gastropoda by Bouchet & Rocroi, 2005).
Fossil record
The genus '' E ...
IUCN
The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...
in 1996.Wells, 1996, p.35
Fossil content
Fossils recovered from the formation include:Itaboraí snakes at
Fossilworks
Fossilworks is a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database
The Paleobiology Database is an online resource for information on the distribution and classification of fossil animals ...
Fossilworks
Fossilworks is a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database
The Paleobiology Database is an online resource for information on the distribution and classification of fossil animals ...
Fossilworks
Fossilworks is a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database
The Paleobiology Database is an online resource for information on the distribution and classification of fossil animals ...
Fossilworks
Fossilworks is a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database
The Paleobiology Database is an online resource for information on the distribution and classification of fossil animals ...
Iguape Formation
The Iguape Formation ( pt, Formacão Iguape) is a geological formation of the Santos Basin offshore of the Brazilian states of Rio de Janeiro, São Paulo, Paraná and Santa Catarina. The calcarenite, shale, siltstone, marl and conglomerate ...
, contemporaneous formation of the Santos Basin
*
Laguna del Hunco Formation
The Laguna del Hunco Formation or Laguna del Hunco Tuff ( es, Formación Laguna del Hunco, Tufolitas Laguna del Hunco) is a localized Early Eocene (Itaboraian in the SALMA classification) fossiliferous geological formation of the Cañadón Asfalto ...
Klondike Mountain Formation
The Klondike Mountain Formation is an Early Eocene (Ypresian) geological formation located in the northeast central area of Washington state. The formation, named for the type location designated in 1962, Klondike Mountain north of Republic, Wash ...
, contemporaneous fossiliferous formation of Washington State
* La Meseta Formation, contemporaneous fossiliferous formation of Antarctica