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Book Chapter

The Triassic stratigraphic succession of Nakhlak (Central Iran), a record from an active margin

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Marco Balini
Marco Balini
Dipartimento di Scienze della Terra, Università di Milano, Via Mangiagalli 34, 20133 Milano, Italy
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Alda Nicora
Alda Nicora
Dipartimento di Scienze della Terra, Università di Milano, Via Mangiagalli 34, 20133 Milano, Italy
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Fabrizio Berra
Fabrizio Berra
Dipartimento di Scienze della Terra, Università di Milano, Via Mangiagalli 34, 20133 Milano, Italy
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Eduardo Garzanti
Eduardo Garzanti
Dipartimento di Scienze Geologiche e Geotecnologie, Università di Milano-Bicocca, Piazza della Scienza 4, Milano, 20126, Italy
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Marco Levera
Marco Levera
Dipartimento di Scienze della Terra, Università di Milano, Via Mangiagalli 34, 20133 Milano, Italy
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Massimo Mattei
Massimo Mattei
Dipartimento di Scienze Geologiche, Università Roma TRE, Largo San Leonardo Murialdo 1, 00146 Roma, Italy
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Giovanni Muttoni
Giovanni Muttoni
Dipartimento di Scienze della Terra, Università di Milano, Via Mangiagalli 34, 20133 Milano, Italy
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Andrea Zanchi
Andrea Zanchi
Dipartimento di Scienze Geologiche e Geotecnologie, Università di Milano-Bicocca, Piazza della Scienza 4, Milano, 20126, Italy
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Irene Bollati
Irene Bollati
Dipartimento di Scienze della Terra, Università di Milano, Via Mangiagalli 34, 20133 Milano, Italy
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Cristiano Larghi
Cristiano Larghi
Dipartimento di Scienze della Terra, Università di Milano, Via Mangiagalli 34, 20133 Milano, Italy
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Stefano Zanchetta
Stefano Zanchetta
Dipartimento di Scienze della Terra, Università di Milano, Via Mangiagalli 34, 20133 Milano, Italy
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Reza Salamati
Reza Salamati
Geological Survey of Iran, Azadi Square, Meraj Avenue, 13185-1494, Tehran, Iran
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Fathullah Mossavvari
Fathullah Mossavvari
Geological Survey of Iran, Azadi Square, Meraj Avenue, 13185-1494, Tehran, Iran
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Published:
January 01, 2009

Abstract

An important, 2.4 km-thick Triassic succession is exposed at Nakhlak (central Iran). This succession was deformed during the Cimmerian orogeny and truncated by an angular unconformity with undeformed Upper Cretaceous sediments. This integrated stratigraphic study of the Triassic included bed-by-bed sampling for ammonoids, conodonts and bivalves, as well as limestone and sandstone petrographic analyses. The Nakhlak Group succession consists of three formations: Alam (Olenekian–Anisian), Bāqoroq (?Upper Anisian–Ladinian) and Ashin (Upper Ladinian). The Alam Formation records several shifts from carbonate to siliciclastic deposition, the Bāqoroq Formation consists of continental conglomerates and the Ashin Formation documents the transition to deep-sea turbiditic sedimentation.

Petrographic composition has been studied for sandstones and conglomerates. Provenance analysis for Alam and most of the Ashin samples suggests a volcanic arc setting, whereas the samples from the Bāqoroq Formation are related to exhumation of a metamorphic basement. The provenance data, together with the great thickness, the sudden change of facies, the abundance of volcaniclastic supply, the relatively common occurrence of tuffitic layers and the orogenic calc-alkaline affinity of the volcanism, point to sedimentation along an active margin in a forearc setting.

A comparison between the Triassic of Nakhlak and the Triassic succession exposed in the erosional window of Aghdarband (Koppeh Dag, NE Iran) indicates that both were deposited along active margins. However, they do not show the same type of evolution. Nakhlak and Aghdarband have quite different ammonoid faunal affinities during the Early Triassic, but similar faunal composition from the Bithynian to Late Ladinian. These results argue against the location of Nakhlak close to Aghdarband.

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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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