Eastern Alborz Mountains Research Articles

Rapid Estimation of Peak Ground Velocity and Earthquake Location Using Small Magnitude Earthquakes in the Tehran Region, Iran

Online Material: Supplemental tables. The Tehran metropolis is located in an extensive area between the Alborz mountain belt to the north and the central Iranian plateau to the south. Tehran, as the political and economic capital of Iran, is considered one of the most populated cities in the world. From the point of view of vulnerability to natural disasters, Tehran is of great concern because of its basic infrastructures and population concentration. The Alborz mountain belt is a part of the Himalayan–Alps orogenic belt with numerous active faults, including the Mosha reverse fault, the North Tehran thrust fault, the Parchin, the Kahrizak, and the South and North Rey faults, with high seismic potential in the study region (Fig. 1). The Mosha fault is one of the fundamental structures of the central Alborz mountains and is situated north of Tehran. This fault is concave to the north and extends from the edge of the mountain range in the west to the eastern Alborz mountains and can be considered an upthrust in some places and an overthrust in others (Moinfar et al. , 1994; Berberian and Yeats, 1999). The North Tehran fault is the most prominent tectonic structure in the immediate vicinity of Tehran for which the trace is east–west to east‐northeast–west‐southwest and slightly concave to the south (Berberian and Yeats, 1999). The Tehran urban district is extended across thick alluvium layers over bedrock with complex geological structure. Based on historic seismic documents, Tehran is surrounded by several specific faults with return periods of about 150 years, but no damaging earthquake has occurred since 1830 (Moinfar et al. , 1994; Berberian and Yeats, 1999), when an estimated 45,000 …

Cambrian (Furongian) rhynchonelliform brachiopods from the Eastern Alborz Mountains, Iran

The Cambrian (Furongian) shallow water carbonates in the Mila Formation in the Tuyeh-Darvar area (eastern Alborz, northern Iran) contain numerous shell beds, entirely composed of disarticulated val ...

First report of craniide brachiopods in the Palaeozoic of Iran (Pseudocrania, Ordovician), and Early to Mid‐Ordovician biogeography of the Craniida

Abstract: Lower Ordovician faunas of Bohemia (Perunica), Baltica and North China include the oldest known representatives of the Order Craniida, but otherwise in Gondwana and associated terranes, the record of craniides is sparse. Pseudocrania insperata sp. nov. from the Lashkarak Formation of the Eastern Alborz Mountains is the first and as yet only record of the occurrence of craniides in the Middle Ordovician (Darriwilian) of Iran and temperate to high latitude peri‐Gondwana. Pseudocrania was known hitherto only from the Middle Ordovician of Baltoscandia and the Chu‐Ili terrane of Kazakhstan.

Late Jurassic (Oxfordian, Bifurcatus and Bimammatum zones) ammonites from the eastern Alborz Mountains, Iran; second part

Late Jurassic (Oxfordian, Bifurcatus and Bimammatum zones) ammonites from the eastern Alborz Mountains, Iran; second part

Early Ordovician (Tremadocian) brachiopods from the Eastern Alborz Mountains, Iran

Early Ordovician (Tremadocian) brachiopods from the Eastern Alborz Mountains, Iran

Late Jurassic (Oxfordian, Bimammatum Zone) ammonites from the eastern Alborz Mountains, Iran

Late Jurassic (Oxfordian, Bimammatum Zone) ammonites from the eastern Alborz Mountains, Iran

Facies features and paleoenvironmental reconstruction of the Early to Middle Devonian syn-rift volcano-sedimentary succession (Padeha Formation) in the Eastern-Alborz Mountains, NE Iran

The Padeha Formation in the Eastern-Alborz Mountains (northeast Iran) is an Early to Middle Devonian syn-rift succession. Siliciclastic rocks (conglomerates, sandstones, mudstones, and red paleosols) to non-marine carbonates (yellowish calcretes, dolocretes, stromatolites, and sandy bivalve packstone) associated with volcaniclastic rocks (basalts or andesites and tuffs) are present in this succession. Facies analysis led to the recognition of three facies associations that are deposited in three terrestrial environments (alluvial fan, distal fan, and palustrine/lacustrine). Its sedimentary fill pattern and association with mafic volcaniclastic rocks indicate that this formation is related to the initial phase of a rift basin (intracratonic rift). Paleosols of this formation are good indicators for recognition of paleoenvironmental factors (climatic changes from semi-arid to sub-humid with annual fluctuation, small and short gross-like vegetation cover, subaerial exposure, very shallow lake, volcanic source rocks, and early meteoric diagenesis).

Lithostratigraphy of the Upper Triassic–Middle Jurassic Shemshak Group of Northern Iran

Abstract The Upper Triassic–lower Middle Jurassic Shemshak Group is a siliciclastic unit, up to 4000 m in thickness, which is widespread across the Iran Plate of northern and central Iran. The group is sandwiched between two major unconformities: the contact with the underlying platform carbonates of the Elikah and Shotori formations is characterized by karstification and bauxite–laterite deposits; the top represents a sharp change from siliciclastic rocks to rocks of a Middle–Upper Jurassic carbonate platform–basin system. In the Alborz Mountains, the group consists of a Triassic and a Jurassic unit, separated by an unconformity, which is in part angular in the northern part of the mountain range and less conspicuous towards the south. Published lithostratigraphic schemes are based on insufficient biostratigraphic and lithological information. Here we present a new lithostratigraphic scheme for the central and eastern Alborz Mountains modified and enlarged from an unpublished report produced in 1976. Two major facies belts, a northern and a southern belt running more or less parallel to the strike of the mountain chain, can be distinguished. In the north, the Triassic part of the group is composed of the comparatively deep-marine Ekrasar Formation with the Galanderud Member (new name) at the base followed by the Laleband Formation, which represents prodelta–delta front environments. Up-section, the latter is replaced by the fluvial–lacustrine, coal-bearing Kalariz Formation. The equivalent Triassic lithostratigraphic unit in the south is the Shahmirzad Formation, redefined here, with the Parvar Member at the base. The formation represents fluvial, coastal plain and shallow- to marginal-marine environments. In the north, the Jurassic part of the group consists exclusively of the Javaherdeh Formation, coarse conglomerates of alluvial fan–braided river origin, which towards the south grades into the Alasht Formation, rocks of fluvial–lacustrine origin with coal. Further south, the Alasht Formation represents intertonguing marginal-marine–flood-plain environments and is followed by the Shirindasht Formation, sandstones and siltstones, indicative of the storm-dominated shelf, and the Fillzamin Formation (new), which is characterized by comparatively deep-marine shales. In the south, the group ends with the Dansirit Formation of deltaic–coastal-plain origin. This lithostratigraphic scheme reflects the tectono-sedimentary evolution of the Shemshak Foreland Basin of the Alborz Mountains where, during the Late Triassic, a relict marine basin in the north became gradually infilled, whereas in the south non-sedimentation and subaerial erosion prevailed and sediments record largely non-marine–marginal-marine conditions. During the early Lias, the basin was filled with erosional debris of the rising Cimmerian Mountain Chain, deposited largely in non-marine environments. During the early Middle Jurassic, in contrast, rapid subsidence in the south resulted in the deepening and subsequent infilling of a marine basin.

BILLENGSELLIDE AND ORTHIDE BRACHIOPODS: NEW INSIGHTS INTO EARLIEST ORDOVICIAN EVOLUTION AND BIOGEOGRAPHY FROM NORTHERN IRAN

Abstract: The eastern Alborz Mountains of Iran comprise a significant peri‐Gondwanan terrane relevant to the early evolution of late Cambrian – early Ordovician brachiopods incorporated into the emerging benthic biota of the Paleozoic Evolutionary Fauna. A low diversity brachiopod assemblage from the late Tremadocian unit of the Lashkarak Formation contains six new species including the polytoechioideans Polytoechia and Protambonites and the orthoideans Paralenorthis, Ranorthis, Tarfaya and Xianorthis. The fauna preserves the earliest records of Polytoechia, unknown previously outside Laurentia and the Uralian margin of Baltica, and of Paralenorthis and Ranorthis, which were widespread along Gondwanan margins and in Baltica from the Floian (Arenig), plus Xianorthis, known hitherto only from the Floian of South China. The enigmatic Tarfaya has an impunctate shell fabric and setigerous perforations along the posterior margin, indicating placement within the Orthoidea in a new Family Tarfayidae. New species of Polytoechia, Protambonites, Paralenorthis, Ranorthis, Tarfaya, Xianorthis are described.

Early to Middle Ordovician lingulate brachiopods from the Lashkarak Formation, Eastern Alborz Mountains, Iran

Popov, L.E., Ghobadi Pour, M. & Hosseini, M., March, 2008. Early to Middle Ordovician lingulate brachiopods from the Lashkarak Formation, Eastern Alborz Mountains, Iran. Alcheringa 32, 1–35. ISSN 0311-5518. Low- to moderate-diversity faunas of lingulate brachiopods are reported for the first time from the Lower to Middle Ordovician Lashkarak Formation of the Eastern Alborz Mountains in northern Iran. Twenty-three species of 20 genera referable to four successive lingulate brachiopod assemblages are systematically described, including Aipyotreta conferta sp. nov., Ghavidelia damghanensis gen. et sp. nov. and Thysanotos multispinulosus sp. nov. The occurrence of Alichovia and Acrotreta, and the early appearance of Biernatia suggest Baltic affinities of the fauna, but scaphelasmatids and Myotreta are missing in the Iranian section. The opportunistic Thysanotos – Leptembolon Association appears in Eastern Alborz in the lower Floian prior to the onset of the carbonate sedimentation.

A new Middle Ordovician arthropod fauna (Trilobita, Ostracoda, Bradoriida) from the Lashkarak Formation, Eastern Alborz Mountains, northern Iran

The first Middle Ordovician trilobites, ostracods and a bradoriid from northern Iran are documented from the Lashkarak Formation. The discovery provides new data bearing on the biogeographical distribution of arthropods and the palaeogeographical setting of northern Iran during the Ordovician. The ostracods include the palaeocopes Cerninella aryana and Ordovizona amyitisae that provide a biostratigraphical tie with horizons of Middle Ordovician (Darriwilian) age in the upper Shirgesht Formation of east central Iran, whilst the trilobites comprise Neseuretus aff. tristani that resembles material from the Tabuck Formation of Saudi Arabia, and Ningkianites sp., a genus characteristic of south Chinese Ordovician faunas. The appearance of Neseuretus in the Lashkarak Formation coincides with the termination of carbonate accumulating facies interpreted as a fall in sea level. The geologically late occurrence of a bradoriid may represent the vestige of a once globally distributed Cambrian arthropod group.

Toarcian and Aalenian (Jurassic) ammonites from the Shemshak Formation of the Jajarm area (eastern Alborz, Iran)

In the Jajarm area (eastern Alborz Mountains, NE Iran) the ?Upper Triassic — Lower Bajocian siliciclastic Shemshak Formation is up to 2000 m thick. Whereas the lower third of the formation is nearly exclusively non-marine, the upper two-thirds are fully marine. The middle part is characterized by several levels containing a relatively diverse and well preserved assemblage of ammonites of the Toarcian to Aalenian stages. Two sections of the ammonite-bearing strata, spaced 20 km, are presented and correlated by means of ammonite biostratigraphy. The ammonite fauna consists of 27 taxa, some of which are recorded for the first time from the Alborz Mountains. The ammonites are briefly described and their palaeobiogeographic context is reviewed. The ammonite fauna of the Shemshak Formation at Jajarm, as elsewhere in North and Central Iran, is exclusively Northwestern Tethyan in character and is closely related to the faunas of Northwestern and Central Europe.

The first record of Astragalus sect. Aegacantha (Fabaceae) in Iran

A new distinct population of Astragalus leiosemius. hitherto unknown to science, is reported for the first time from the eastern Alborz mountains in the Irano‐Turanian part of Iran, at an altitude of 2400 m, far disjunct (ca. 800 km) from the populations at the Asia media and Afghanistan. The new taxon is described and illustrated as Astragalus leiosemius subsp. sabzevarensis. This orophilous and tragachantic plant belongs to A. sect. Aegacantha. On the basis of some important data on morphology, ecology and chorology, the new taxon is reported and its affinities and differences with regard to close taxa are presented. A. sect Aegacantha is recorded for the first time from the eastern part Iran.

Trilobites Asteropyginae dévoniens d’Iran

Ten species of trilobites belonging to 4 genera of the sub-family Asteropyginae DELO are described from the Devonian (Givetian-Frasnian) of Iran. Three of which are new: Neocalmonia lutensis nov. sp., Neocalmonia yazdii nov. sp. and Radiopyge sardarensis nov. sp. The study of this material have required the revision of Heliopyge sharudensis (PILLET, 1974) from the Givetian of the Eastern Alborz Mountains and of Neocalmonia quadricosta PILLET, 1969, type-species of the genus Neocalmonia, from the Frasnian of Afghanistan. The recognition of genera and species in common with the Givetian and the Frasnian of Afghanistan emphasizes the close relations between these two regions. The genera Bradocryphaeus, Heliopyge, Neocalmonia, Radiopyge, represented by related species, are likewise present in Iran, Afghanistan and Western Europe. Their presence confirms that these regions belong, during the Devonian, to the North Gondwanian domain.