5th Swiss Geoscience Meeting, Geneva 2007
Local tectonic controls on deposition of Permian mixed
siliciclastic-carbonate deposits of Khan Formation
along Kalmard fault, central Iran
Shadan Mahdi* & Hosseini-Barzi Mahboobeh*
*Faculty of earth sciences, geology department, Shahid-Beheshti University, Tehran,
Iran (hosseini@khayam.ut.ac.ir)
Permian is the time of worldwide changes in the climate and sea-level (Ross
and Ross, 1988) and extensive epirogenies and extinctions (Angiolini et al.,
2003); when Neotethys began to open and the Central Iran micro-continent as a
part of Eurasia, take apart from Gondwana land and going to move toward the
upper latitudes (Glennie, 2000). In spite of these regional evolution, the local
movements of some fault-bounded blocks produced spatial changes in the
evolution of Permian lands in Central Iran. N-NE trending Kalmard fault is one
of the major basement faults in Central Iran which separates the Tabas block to
the west from Posht-e Badam block to the east of different evolutional history
(Fig. 1a) (Aghanabati, 1977). The study of fusulinid fauna indicate that during
late Sakmarian to early Artinskian, deposition of Khan Formation in Posht-e
Badam block corresponds to a major unconformity in the Tabas block (Davydov
and Arefifard, 2007).
Detail sampling and field investigations of siliciclastic beds of the Khan
formation along the Kalmard Fault were made across two sections 30 km apart
(Fig. 1b). Hanging fusulinid bearing units reported by Davydov and Arefifard
(2007), we correlated the two sections and recognized three sedimentary cycles
(Fig. 1c). Using conglomerate and quartzarenite beds accompanied with laterite
and iron rich horizons, we divided two of these cycles into two sub-cycles in the
northern section (Chahroof in Fig. 1c) Moreover, in this section an increase in
siliciclastic sediments thicknesses (clastic input) can be seen in cycle 1 (from 12
m in south to 17 m in north), cycle 2 (from 20 m in south to 21 m in north) and
cycle 3 (from 18 m in south to at least 20 m in north). In addition, in northern
section, not only the erosion at the top of the cycle 3 of the Khan formation is
more developed but also the unconformably overlying sediments are younger
(Triassic) compared to the southern section which are Jurassic in age
(Cheshmeh bakhshi section in Fig. 1c). These evidences suggest that tectonic
movements due to activity along the Kalmard fault were more severe in
northern parts of the Posht-e Badam block during late Sakmarian to early
Artinskian. Dolomitization of the limestone beds in cycle 2 of the
Cheshmebakhshi section, however, could be related to the migration of tectonic
driven fluids from north to south along the Kalmard fault. We conclude that such
sedimentary evidence can be used to better understand the characretristics and
details of paleo-tectonic evolution of the central Iran region.
Figuer 1: a) location of Posh-e Badam block in central Iran; b) localitions of
studied sections in Posh-e Badam block; c) stratigraphic culomns and
sedimentary cycles in the sections (ages in Fig. 1c and Fig. 1a and b, modified
afre Davydove and Arefifard, 2007).
5th Swiss Geoscience Meeting, Geneva 2007
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