The Dansirit Formation is a

geological 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 expo ...

Iran Iran, officially the Islamic Republic of Iran (IRI) and also known as Persia, is a country in West Asia. It borders Iraq to the west, Turkey, Azerbaijan, and Armenia to the northwest, the Caspian Sea to the north, Turkmenistan to the nort ...

. It is

Middle Jurassic The Middle Jurassic is the second Epoch (geology), epoch of the Jurassic Period (geology), Period. It lasted from about 174.1 to 161.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relativel ...

in age, dating from the

Aalenian The Aalenian () is a subdivision of the Middle Jurassic Epoch/Series of the geologic timescale that extends from about 174.7 ±0.8 Ma to about 170.9 ±0.8 Ma (million years ago). It was preceded by the Toarcian and succeeded by the Bajocian. St ...

Bajocian In the geologic timescale, the Bajocian is an age and stage in the Middle Jurassic. It lasted from approximately 170.9 ±0.8 Ma to around 168.2 ±1.2 Ma (million years ago). The Bajocian Age succeeds the Aalenian Age and precedes the Bathonia ...

Fossils

The fossils of Dansirit Formation mainly include plant fossils and dinosaur footprints Plant fossils Plant fossils of the Dansirit Formation mostly include

Filicales The Polypodiidae, commonly called leptosporangiate ferns, formerly Leptosporangiatae, are one of four subclasses of ferns, the largest of these being the largest group of living ferns, including some 11,000 species worldwide. The group has also ...

Bennettitales Bennettitales (also known as cycadeoids) is an extinct order of seed plants that first appeared in the Permian period and became extinct in most areas toward the end of the Cretaceous. Bennettitales were amongst the most common seed plants of th ...

Cycadales Cycads are seed plants that typically have a stout and woody (ligneous) trunk with a crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, that is, individual plants of a species are either male or ...

Corystospermales Corystosperms are a group of extinct seed plants (often referred to as "seed ferns") belonging to the family Corystospermaceae (also called Umkomasiaceae) assigned to the order Corystospermales or Umkomasiales. They were first described based on ...

Caytoniales The Caytoniales (Figs. 1-2) are an extinct order of seed plants known from fossils collected throughout the Mesozoic Era, around . They are regarded as seed ferns because they are seed-bearing plants with fern-like leaves. Although at one time c ...

Czekanowskiales Czekanowskiales, also known as Leptostrobales, are an extinct group of seed plants. Members of the family are distinguished by persistent leaves borne on deciduous short shoots, subtended by scale-like leaves. The leaves are highly dissected (d ...

Ginkgoales Ginkgoales are a gymnosperm Order (biology), order containing only one Neontology, extant species: ''Ginkgo biloba'', the ginkgo tree. The order has a long fossil record extending back to the Early Permian around 300 million years ago from fossi ...

and

Pinales The order Pinales in the division Pinophyta, class Pinopsida, comprises all the extant conifers. The distinguishing characteristic is the reproductive structure known as a cone produced by all Pinales. All of the extant conifers, such as Arauca ...

. Filicophyta, Coniferales, Bennetitales and Equisetales dominate the flora, which indicates the deposition of this formation in relatively tropical and rainy environments in islands, deltas and river banks. Dinosaur footprints The dinosaur footprints of this formation in Mazandaran province include

theropods Theropoda (; from ancient Greek , (''therion'') "wild beast"; , (''pous, podos'') "foot"">wiktionary:ποδός"> (''pous, podos'') "foot" is one of the three major groups (clades) of dinosaurs, alongside Ornithischia and Sauropodom ...

with an average length of about 2 meters, small two-toed Deinonychosaurs, relatively giant

sauropods Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their b ...

about 9 meters long, and small two-legged

ornithopods Ornithopoda () is a clade of ornithischian dinosaurs, called ornithopods (). They represent one of the most successful groups of herbivore, herbivorous dinosaurs during the Cretaceous. The most primitive members of the group were bipedal and rel ...

. These works are limited to footprints and dinosaur fossils have not been reported in this formation.

Description

It is part of the

Shemshak Group The Shemshak Formation is a Mesozoic geologic group in Iran. It is dated to the Norian to the Late Jurassic and is up to 4,000 meters thick and primarily consists of siliciclastic sediments. The most important group in terms of paleontology is t ...

, a

Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch a ...

Callovian In the geologic timescale, the Callovian is an age and stage in the Middle Jurassic, lasting between 165.3 ± 1.1 Ma (million years ago) and 161.5 ± 1.0 Ma. It is the last stage of the Middle Jurassic, following the Bathonian and preceding the ...

set of coal bearing largely fluvio-lacustrine sediments up to 4000 metres thick located within the

Alborz Mountains The Alborz ( ) range, also spelled as Alburz, Elburz or Elborz, is a mountain range in northern Iran that stretches from the border of Azerbaijan along the western and entire southern coast of the Caspian Sea and finally runs northeast and merge ...

. The

outcrop An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth and other terrestrial planets. Features Outcrops do not cover the majority of the Earth's land surface because in most p ...

of sediments is strongly controlled by numerous fault structures in the region. The formation predominantly consists of

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

, with subordinate

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility. Although its permeabil ...

and

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of Clay mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...

. Dinosaur tracks are known from the formation, including sauropods, and tridactyl and didactyl theropods. A diverse fossil flora is also known from the formation.

References

{{reflist Geologic formations of Iran Jurassic System of Asia Middle Jurassic Asia Aalenian Stage Bajocian Stage Sandstone formations Fluvial deposits Lacustrine deposits Ichnofossiliferous formations Paleontology in Iran

Fossils

Description

See also

References