The Triassic stratigraphic succession of Nakhlak (Central Iran), a record from an active margin
Capitolo
Data di Pubblicazione:
2009
Citazione:
The Triassic stratigraphic succession of Nakhlak (Central Iran), a record from an active margin / M. Balini, A. Nicora, F. Berra, E. Garzanti, M. Levera, M. Mattei, G. Muttoni, A. Zanchi, I. Bollati, C. Larghi, S. Zanchetta, R. Salamati, F. Mossavari - In: South Caspian to Central Iran Basins / [a cura di] M.F. Brunet, M. Wilmsen, J.W. Granath. - London : Geological Society of London, 2009. - ISBN 978-1862392717. - pp. 287-321
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), Ba¯qoroq (?Upper Anisian–Ladinian) and Ashin (Upper
Ladinian). The Alam Formation records several shifts from carbonate to siliciclastic deposition,
the Ba¯qoroq 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 Ba¯qoroq 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.
Tipologia IRIS:
03 - Contributo in volume
Elenco autori:
M. Balini, A. Nicora, F. Berra, E. Garzanti, M. Levera, M. Mattei, G. Muttoni, A. Zanchi, I. Bollati, C. Larghi, S. Zanchetta, R. Salamati, F. Mossavari
Link alla scheda completa:
Titolo del libro:
South Caspian to Central Iran Basins