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Book Chapter

Pennsylvanian–Early Triassic stratigraphy in the Alborz Mountains (Iran)

By
Maurizio Gaetani
Maurizio Gaetani
1
Dipartimento di Scienze della Terra
,
Università di Milano
,
Via Mangiagalli 34, 20133 Milano
,
Italy
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Lucia Angiolini
Lucia Angiolini
1
Dipartimento di Scienze della Terra
,
Università di Milano
,
Via Mangiagalli 34, 20133 Milano
,
Italy
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Katsumi Ueno
Katsumi Ueno
2
Department of Earth System Science, Faculty of Science
,
Fukuoka University
,
Fukuoka 814-0180
,
Japan
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Alda Nicora
Alda Nicora
1
Dipartimento di Scienze della Terra
,
Università di Milano
,
Via Mangiagalli 34, 20133 Milano
,
Italy
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Michael H. Stephenson
Michael H. Stephenson
3
British Geological Survey
,
Kingsley Dunham Centre Keyworth, Nottingham NG12 5GG
,
UK
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Dario Sciunnach
Dario Sciunnach
4
Regione Lombardia, Infrastruttura per l’Informazione Territoriale
,
Via Sassetti 32, 20124 Milano
,
Italy
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Roberto Rettori
Roberto Rettori
5
Dipartimento di Scienze della Terra
,
Università di Perugia
,
Piazza Università 1, 06100 Perugia
,
Italy
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Gregory D. Price
Gregory D. Price
6
School of Earth, Ocean and Environmental Sciences
,
University of Plymouth
,
Drake Circus, Plymouth PL4 8AA
,
UK
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Jafar Sabouri
Jafar Sabouri
7
Geological Survey of Iran
,
Azhad Square, Tehran
,
Iran
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Published:
January 01, 2009

Abstract

New fieldwork was carried out in the central and eastern Alborz, addressing the sedimentary succession from the Pennsylvanian to the Early Triassic. A regional synthesis is proposed, based on sedimentary analysis and a wide collection of new palaeontological data. The Moscovian Qezelqaleh Formation, deposited in a mixed coastal marine and alluvial setting, is present in a restricted area of the eastern Alborz, transgressing on the Lower Carboniferous Mobarak and Dozdehband formations. The late Gzhelian–early Sakmarian Dorud Group is instead distributed over most of the studied area, being absent only in a narrow belt to the SE. The Dorud Group is typically tripartite, with a terrigenous unit in the lower part (Toyeh Formation), a carbonate intermediate part (Emarat and Ghosnavi formations, the former particularly rich in fusulinids), and a terrigenous upper unit (Shah Zeid Formation), which however seems to be confined to the central Alborz. A major gap in sedimentation occurred before the deposition of the overlying Ruteh Limestone, a thick package of packstone–wackestone interpreted as a carbonate ramp of Middle Permian age (Wordian–Capitanian). The Ruteh Limestone is absent in the eastern part of the range, and everywhere ends with an emersion surface, that may be karstified or covered by a lateritic soil.

The Late Permian transgression was directed southwards in the central Alborz, where marine facies (Nesen Formation) are more common. Time-equivalent alluvial fans with marsh intercalations and lateritic soils (Qeshlaq Formation) are present in the east. Towards the end of the Permian most of the Alborz emerged, the marine facies being restricted to a small area on the Caspian side of the central Alborz. There, the Permo-Triassic boundary interval is somewhat similar to the Abadeh–Shahreza belt in central Iran, and contains oolites, flat microbialites and domal stromatolites, forming the base of the Elikah Formation. The PT boundary is established on the basis of conodonts, small foraminifera and stable isotope data. The development of the lower and middle part of the Elikah Formation, still Early Triassic in age, contains vermicular bioturbated mudstone/wackestone, and anachronostic-facies-like gastropod oolites and flat pebble conglomerates.

Three major factors control the sedimentary evolution. The succession is in phase with global sea-level curve in the Moscovian and from the Middle Permian upwards. It is out of phase around the Carboniferous–Permian boundary, when the Dorud Group was deposited during a global lowstand of sealevel. When the global deglaciation started in the Sakmarian, sedimentation stopped in the Alborz and the area emerged. Therefore, there is a consistent geodynamic control. From the Middle Permian upwards, passive margin conditions control the sedimentary evolution of the basin, which had its depocentre(s) to the north. Climate also had a significant role, as the Alborz drifted quickly northwards with other central Iran blocks towards the Turan active margin. It passed from a southern latitude through the aridity belt in the Middle Permian, across the equatorial humid belt in the Late Permian and reached the northern arid tropical belt in the Triassic.

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Contents

Geological Society, London, Special Publications

South Caspian to Central Iran Basins

M.-F. Brunet
M.-F. Brunet
CNRS-INSU and Université Pierre et Marie Curie, France
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M. Wilmsen
M. Wilmsen
Senckenberg Naturhistorische Sammlungen Dresden, Museum für Mineralogie und Geologie, Germany
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J. W. Granath
J. W. Granath
Granath & Associates Consulting Geology, USA
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Geological Society of London
Volume
312
ISBN electronic:
9781862395602
Publication date:
January 01, 2009

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