The Triassic stratigraphic succession of Nakhlak (Central Iran), a record from an active margin
Marco Balini, Alda Nicora, Fabrizio Berra, Eduardo Garzanti, Marco Levera, Massimo Mattei, Giovanni Muttoni, Andrea Zanchi, Irene Bollati, Cristiano Larghi, Stefano Zanchetta, Reza Salamati, Fathullah Mossavvari, 2009. "The Triassic stratigraphic succession of Nakhlak (Central Iran), a record from an active margin", South Caspian to Central Iran Basins, M.-F. Brunet, M. Wilmsen, J. W. Granath
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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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This book combines interdisciplinary research results using structural geology, geophysics, sedimentology, stratigraphy, palaeontology, palaeomagnetism and subsidence modelling obtained through the MEBE (Middle East Basins Evolution) Programme and other groups in the South Caspian and Northern and Central Iran.
A great part of the volume is devoted to Northern Iran (Alborz, Binalud and Koppeh Dagh belts), dealing mainly with the Late Palaeozoic and the Mesozoic Eras. Two papers present subsidence models of the South Caspian Basin since the Jurassic and three papers focus on Central Iran.
The data and models in this compilation of papers present a detailed picture and a very comprehensive understanding of the Late Palaeozoic to Cenozoic evolution of the South Caspian and North Iran to Central Iran basins. Geodynamic evolution and sedimentation are mainly controlled by the closure of the Palaeo–Tethys due to collision of Eocimmerian blocks with south Laurasia, opening of the South Caspian Basin, and Neo–Tethys ocean closure associated with Arabia–Eurasia collision.