The Shemshak Formation is a

Mesozoic The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...

geologic group In geology, a group is a lithostratigraphic unit consisting of a series of related formations that have been classified together to form a group. Formations are the fundamental unit of stratigraphy. Groups may sometimes be combined into superg ...

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 dated to the

Norian The Norian is a division of the Triassic geological period, Period. It has the rank of an age (geology), age (geochronology) or stage (stratigraphy), stage (chronostratigraphy). It lasted from ~227.3 to Mya (unit), million years ago. It was prec ...

to the

Late Jurassic The Late Jurassic is the third Epoch (geology), epoch of the Jurassic Period, and it spans the geologic time scale, geologic time from 161.5 ± 1.0 to 143.1 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic stratum, strata.Owen ...

and is up to 4,000 meters thick and primarily consists of

siliciclastic Siliciclastic (or ''siliclastic'') rocks are clastic noncarbonate sedimentary rocks that are composed primarily of silicate minerals, such as quartz or clay minerals. Siliciclastic rock types include mudrock, sandstone Sandstone is a Clastic ...

sediments. The most important group in terms of paleontology is the Mesozoic in Iran. Contains dinosaur fossils, plant flora with rich coal deposits, and other animals.Weishampel, et al. (2004). "Dinosaur distribution." Pp. 517-607. Zamites_persica

Fossils and paleoenvironment

The Shemshak Group in Iran includes formations that sometimes leave behind marine sediments. This section introduces all the fossil animals reported from this group. Land animals:

Dinosaurs

* theropod, Fossil teeth and dozens of

fossil footprints A fossil track or ichnite (Greek "''ιχνιον''" (''ichnion'') – a track, trace or footstep) is a fossilized footprint. This is a type of trace fossil. A fossil trackway is a sequence of fossil tracks left by a single organism. Over the year ...

Sauropoda Sauropoda (), whose members are known as sauropods (; from ''wikt:sauro-, sauro-'' + ''wikt:-pod, -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative t ...

, Several fossil tracks *

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

, Several fossil tracks *

Stegosauria Stegosauria is a group of Herbivore, herbivorous ornithischian dinosaurs that lived during the Jurassic and early Cretaceous Period (geology), periods. Stegosaurian fossils have been found mostly in the Northern Hemisphere (North America, Europe a ...

, Several fossil tracksPalaeoichnology and Palaeontology of Dinosaurs in North of Kerman, South East Central Iran

Insects

Cupedidae The Cupedidae are a small family of beetles, notable for the square pattern of "windows" on their elytra (hard forewings), which give the family their common name of reticulated beetles. The family consists of about 30 species in 9 genera, with ...

Rhaetian The Rhaetian is the latest age (geology), age of the Triassic period (geology), Period (in geochronology) or the uppermost stage (stratigraphy), stage of the Triassic system (stratigraphy), System (in chronostratigraphy). It was preceded by the N ...

Alborz Province Alborz province () is one of the 31 provinces of Iran. Its capital is the city of Karaj, which lies 10 km west of Tehran, at the foothills of the Alborz mountains. Alborz is Iran's smallest province in area. History In 2010, Karaj ...

Roachoid "Roachoids", also known as "Roachids", "Blattoids" or Eoblattodea, are members of the stem group of Dictyoptera (the group containing modern cockroaches, termites and praying mantises). They generally resemble cockroaches, but most members, unl ...

* Odonatan, Some

egg An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the ...

Lower Jurassic The Early Jurassic Epoch (in chronostratigraphy corresponding to the Lower Jurassic Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic–Jurassic extinction event, 201.3 Ma&nb ...

Gilan Province Gilan Province () is one of the 31 provinces of Iran, in the northwest of the country and southwest of the Caspian Sea. Its capital is the city of Rasht. The province lies along the Caspian Sea, in Iran's Regions of Iran, Region 3, west of ...

Xyelidae The Xyelidae are a comparatively species-poor family of sawflies, comprising about 80 extant species in five genera worldwide, and is the only family in the superfamily Xyeloidea. The fossil record of the family is extensive, comprising more than ...

, Nutritional effects on leaves,

* Large amounts of insect eggs and insect damage on leaves

plants

Plant fossils of the Shemshak Group mostly include Filicales,

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 ...

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,

Conifer Conifers () are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a sin ...

ales, Bennetitales and

Equisetales Equisetales is an order of subclass Equisetidae with only one living family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relation ...

dominate the flora, which indicates the deposition of this formation in relatively tropical and rainy environments in islands, deltas and river banks.

> cycads

Nilssoniopteris ''Nilssoniopteris'' is an extinct form genus of leaves belonging to the Bennettitales. Leaves are slender and often entire-margined (smooth-edged), though some species have dissected leaves with numerous small segments extending down to the rachi ...

, Golestan Province * Nilssonia,

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 ...

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 ...

Isfahan Isfahan or Esfahan ( ) is a city in the Central District (Isfahan County), Central District of Isfahan County, Isfahan province, Iran. It is the capital of the province, the county, and the district. It is located south of Tehran. The city ...

, South Khorasan *Anomozamites,

, Golestan Province *Scytophyllum,

, Golestan Province * Ctenis,

, South Khorasan *

Pterophyllum ''Pterophyllum'' is a small genus of freshwater fish from the family Cichlidae known to most aquarists as angelfish. All ''Pterophyllum'' species originate in the Amazon Basin, Orinoco Basin and various rivers in the Guiana Shield in tropical ...

* Scytophyllum *

Taeniopteris ''Taeniopteris'' is an Extinction, extinct form genus of Mesozoic vascular plant leaves, perhaps representing those of Cycad, cycads, Bennettitales, bennettitaleans, or Marattiales, marattialean ferns. The form genus is almost certainly a polyphy ...

*Anthrophyopsis,

, Golestan Province

> Bennettitales

* Zamites,

, Golestan Province *

Ptilophyllum ''Ptilophyllum'' is an extinct form genus of leaves belonging to the extinct seed plant order Bennettitales. The leaves, like other Bennettitales morphogenera are generally pinnate Pinnation (also called pennation) is the arrangement of feathe ...

, South Khorasan *

Otozamites ''Otozamites'' is a genus of plants in the order Bennettitales and the family Williamsoniaceae. The leaves are usually ovate to slightly lanceolate and have branched veins. The genus is found on all continents, although it is more widespread in ...

, Golestan Province * Williamsonia,

, Golestan Province

> Ferns

* Phlebopteris,

, Golestan, South Khorasan *

Cladophlebis ''Cladophlebis'' is an extinct form genus of fern, which has been reported from the Permian to the end of the Cretaceous and from all continents of the world. Description Some pinnules have smooth edges and some have serrated edges. The midr ...

, Golestan,

, South Khorasan *Clathropteris,

, Golestan Province *Lobifolia,

, Golestan Province *Dictyophyllum,

, Golestan, South Khorasan *Todites,

, Golestan, South Khorasan *

Coniopteris ''Coniopteris'' is an extinct genus of Mesozoic fern leaves. It was widespread over both hemispheres during the Jurassic and Early Cretaceous, with over 130 species having been described. Most species of ''Coniopteris'' probably had a herbaceous h ...

, South KhorasanMiddle Jurassic plant macro and microfossils from Shahreza, South West Isfahan, Central Iran: Palaeoclimate influences *Marattiopsis,

, South Khorasan *Ferizianopteris,

, South Khorasan *Lobifolia,

, South Khorasan.

> Ginkgoopsida

Ginkgoites ''Ginkgoites'' is a genus of extinct plants belonging to Ginkgoaceae. Fossils of these plants have been found around the globe during the Triassic, Jurassic, Cretaceous, with fossils also known from the Paleogene. The name was created as a form g ...

, South Khorasan * Baier,

, Golestan Province *Stachyopitys,

, Golestan Province *

Sphenobaiera ''Sphenobaiera'' is a form genus for plant leaves belonging to the order Ginkgoales found in rocks from Triassic to Cretaceous periods. The genus ''Sphenobaiera'' is used for plants with wedge-shaped leaves that can be distinguished from ''Ginkg ...

> Conifers

*Podozamites,

, Golestan,

, South Khorasan *Chamaetaxus,

, Golestan Province * Elatocladus,

*Elatides,

, South Khorasan *Cyparissidium,

*Klukia,

, South Khorasan

> Pteridospermatophyta

Sphenopteris ''Sphenopteris'' is a genus of seed ferns containing the foliage of various extinct plants, ranging from the Devonian to Late Cretaceous. One species, ''S. höninghausi'', was transferred to the genus '' Crossotheca'' in 1911. Biology The fro ...

, Golestan, South Khorasan *

Caytonanthus ''Caytonanthus'' is an extinct genus of seed ferns. Description ''Caytonanthus'' is the polliniferous organ-genus of the Caytoniales, and it is often found along ''Sagenopteris ''Sagenopteris'' is a genus of extinct seed ferns from the Tria ...

Pachypteris ''Pachypteris'' is a Mesozoic pteridosperm ("seed fern") genus of fossil leaves. It has either been aligned with the peltasperms or the corystosperms. Description ''Pachypteris'' is represented by hypostomatic, bipinnate or unipinnate leav ...

> Equisetidae

Equisetites ''Equisetites'' is an extinct genus of vascular plants within Equisetaceae, a family of vascular plants that reproduce by spores rather than seeds. The genus was named by Sternberg (1833)K. Sternberg, von Graf. (1833). Versuch einer geognostisch- ...

, Golestan,

, South Khorasan *

Neocalamites ''Neocalamites'' is an extinct genus of equisetalean plant. ''Neocalamites'' thrived during the Permian and Triassic, and occurs worldwide. Description According to Elgorriaga et al. 2018, characteristics of ''Neocalamites'' include: "(1) aeria ...

, Golestan, South Khorasan *Annulariopsis,

, South KhorasanBiostratigraphy of plant macrofossils of Hojedk Formation in the Chah-Rekhneh area, South-West Tabas and its palaeoclimate analysis *beanii,

> Other plants

, Golestan,

, South Khorasan *Chamaetaxus,

*Rhizomopteris,

, South Khorasan

Other animals

Cephalopod A cephalopod is any member of the molluscan Taxonomic rank, class Cephalopoda (Greek language, Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral symm ...

a (

ammonites Ammonoids are extinct, (typically) coiled-shelled cephalopods comprising the subclass Ammonoidea. They are more closely related to living octopuses, squid, and cuttlefish (which comprise the clade Coleoidea) than they are to nautiluses (family N ...

, etc) *

Dactylioceras ''Dactylioceras'' was a widespread genus of ammonites from the Lower Jurassic period, approximately 180 million years ago ( mya).Like many other ammonites, the genus ''Dactylioceras'' is extremely important in biostratigraphy, being a key index ...

Tehran Province Tehran province () is one of the 31 provinces of Iran. Its capital is the city of Tehran. Tehran province covers an area of and is located to the north of the central plateau of Iran. It was made a part of the First Region with its secretar ...

*Leioceras,

, Semnan Province > Bivalvia: *Inoperna,

, Semnan ProvinceThe upper Shemshak Formation (Toarcian–Aalenian) of the Eastern Alborz (Iran): Biota and palaeoenvironments during a transgressive–regressive cycle * Pterotrigonia,

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...

, North Khorasan Province * Trigonia,

, North Khorasan Province > Brachiopod: *juralina,

A colour atlas of Iranian fossils (Book) Plant macrofossils from the Takht Minodasht coal mine, age determination, relative abundance and Sorenson florescence index, and comparison with other florescences in Iran and Eurasia Triassic and Jurassic Floras and Climate of Central-East Iran

Fossil Gallery

A_Shemshak_Group_excavation_site_and_some_of_its_fossils

Description and The way to form

In the Triassic, Iran changed the conditions and type of sedimentary basins of that time as a result of the tectonic forces of a large orogeny called Late

Cimmerian The Cimmerians were an Ancient Iranian peoples, ancient Eastern Iranian languages, Eastern Iranian peoples, Iranic Eurasian nomads, equestrian nomadic people originating in the Pontic–Caspian steppe, part of whom subsequently migrated into W ...

. As a result of the tectonic forces, the young Tethys sea is opening and the Iran plate has been moving away from the

Zagros The Zagros Mountains are a mountain range in Iran, northern Iraq, and southeastern Turkey. The mountain range has a total length of . The Zagros range begins in northwestern Iran and roughly follows Iran's western border while covering much of s ...

Arabian The Arabian Peninsula (, , or , , ) or Arabia, is a peninsula in West Asia, situated north-east of Africa on the Arabian plate. At , comparable in size to India, the Arabian Peninsula is the largest peninsula in the world. Geographically, the ...

plate, and this movement towards the north caused the collision of the Iran and Turan plates and the closure of the old Tethys in the

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 ...

. Orogeny has been associated with the general upliftment of the earth, which until the middle of the Middle Jurassic, that is, about 170 million years ago, formed high landmasses in central Iran and Lut block In Alborz, Farabums were associated with a lot of drift and the landing and residuals of the sea were accompanied, but in the late Triassic, with the advancement of the sea in Alborz, this area has become a relatively narrow bay that extends to the east and is connected to the high sea from the west. In this bay, the subsidence of the bed was high, so that the conditions for the accumulation of a significant amount of mud were fully provided. At this time, with the retreat of the sea, Alborz first became an alluvial-delta plain and then an alluvial plain in which turbine lagoons were sometimes formed. Due to these geographical and climatic conditions at that time, relatively homogeneous shale and sandstone deposits along with coal layers begin to form in these swampy-kulabi environments, which continue to the Middle Jurassic, about 170 million years ago. This uniformity in sedimentation in the late Triassic to Middle Jurassic is such that it is not possible to separate them based on age and in many parts of Alborz are not separated from each other. 1027 meters have been measured in the cutting site of the Setb pattern for the Shamshak formation, but the lateral thickness changes are very large in Alborz places and extend up to about 4000 meters. The Shamshak Group is actually a sedimentary cycle whose deposits indicate the existence of wide plains and marsh-river basins and sometimes shallow seas. This stratified rock unit is one of the most prominent stratified rock units of Iran, which generally has a weathered appearance and dark color. Having a lot of coal, animal and plant fossils has caused many studies to be done on it. In the cutting site of this formation model that Aserto has chosen in the upstream of Rote valley in the north of Lazim pass, he has divided the Shamshak formation into four rock zones: *ower sandstone: 70 to 100 meters thick, including an interval of whitish quartz sandstones with thin layers of shale and coaly shales. *Lower Coal series: including 250 to 300 meters of shale and argillite with intervals of extractable coal *Upper sandstone: 500 to 600 meters of overlying sandstones with mica silt layers and regionally shale and ammonite limestone horizons *Upper coal series: argillaceous deposits and coal layers, where coal is abundant in the lower part and silt, marl and gray shale are more abundant in the upper part.

Naming and age

In 1963, a scientist named Asreto studied this sedimentary row and called the

Alborz 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 ...

coal-fired sediment collection " Sheshmak Formation" and considered its age from the early Jurassic (Lias) to the middle of it (Duger), but subsequent findings showed that the Shemshak Formation is actually It is a sedimentary shrub that can consist of several formations and its age ranges from the

to the

, so the name "Sheshshak Group" was chosen for it.

Formations

Dansirit Formation The Dansirit Formation is a geological formation in Iran. It is Middle Jurassic in age, dating from the Aalenian to Bajocian. Fossils The fossils of Dansirit Formation mainly include plant fossils and dinosaur footprints Plant fossils Plant f ...

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

* Nayband Formation * Shemshak Formation * Badamu Formation * Hojedk Formation

Footnotes

References

* Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. 861 pp. {{ISBN, 0-520-24209-2. Triassic System of Asia Jurassic System of Asia Geologic formations of Iran

Fossils and paleoenvironment

Dinosaurs

Insects

plants

> cycads

> Bennettitales

> Ferns

> Ginkgoopsida

> Conifers

> Pteridospermatophyta

> Equisetidae

> Other plants

Other animals

Fossil Gallery

Description and The way to form

Naming and age

Formations

See also

Footnotes

References