O R I G I N A L P A P E R
The Oligo-/Miocene Qom Formation (Iran): evidence
for an early Burdigalian restriction of the Tethyan Seaway
and closure of its Iranian gateways
M. Reuter
Æ W. E. Piller Æ M. Harzhauser Æ O. Mandic Æ B. Berning Æ
F. Ro¨gl
Æ A. Kroh Æ M.-P. Aubry Æ U. Wielandt-Schuster Æ A. Hamedani
Received: 14 March 2007 / Accepted: 11 October 2007
Ó Springer-Verlag 2007
Abstract
In the central Iranian Esfahan-Sirjan and Qom
basins sedimentation of the Oligo-/Miocene Qom Forma-
tion took place on extensive mixed carbonate–siliciclastic
ramps. During this time, both basins were positioned at the
Eurasian margin of the Tethyan Seaway, which connected
the western and eastern regions of the Tethys Ocean at least
until the late Burdigalian. During the so-called Terminal
Tethyan Event the Tethyan Seaway was then closed due to
the collision of the African/Arabian and Iranian/Eurasian
plates. Facies analysis of the sedimentary record of both
basins indicates paleoenvironments ranging from terrestrial
to open marine settings, including mangrove, restricted
inner shelf lagoon, seagrass meadow, reefal, and deeper
offshore environments. Recognition of eight depositional
sequences and elaboration of an integrated biostratigraphic
framework (calcareous nannoplankton, planktic and larger
benthic foraminifers, gastropods, and pectinids) allow us to
construct a basin-spanning stratigraphy. The assignment of
the recognized sea-level lowstands to the Ru 3 to Bur 3
lowstands of the global sea-level curve enables a compar-
ison with time-equivalent sections from the Zagros Basin,
which was part of the African/Arabian Plate on the
opposing southern margin of the Tethyan Seaway. The so
calibrated sections display restrictions of the Tethyan
Seaway and interruption of the south Iranian gateways
between the Qom Basin and the Proto-Indopacific in rela-
tion to ongoing plate collision during the early Burdigalian.
Keywords
Qom Formation
Á Stratigraphy Á
Terminal Tethyan Event
Á Tethyan Seaway Á Iran
Introduction
Sediments of the Qom Formation have an extensive dis-
tribution in northern and central Iranian Qom and Esfahan-
Sirjan basins (Sto¨cklin and Setudehina
1991
) (Fig.
1
) and
comprise thick successions of marine marls, limestones,
gypsum and siliciclastics. After oil was discovered in
porous bioclastic limestones in 1934 (Mostofi and Gansser
1957
; Abaie et al.
1963
; Rosenberg
1975
) the Qom Fm.
moved into the focus of scientific research. Historical
investigations of the Qom Fm. reach back to Furrer and
Soder (
1955
), who established the type locality near the
town of Qom and defined six lithostratigraphic units (a- to
f-Members: a-Member = basal limestone, b-Member =
sandy marls, c-Member = alternating marls and lime-
stones, d-Member = evaporites, e-Member = green marls,
f-Member = top limestone). Whereas Bozorgnia (
1966
)
recognized two sedimentary cycles in the Qom Fm. at
its type area, Nogole-Sadat (
1985
) identified a third
M. Reuter (
&) Á W. E. Piller Á B. Berning
Institute of Earth Sciences, Graz University,
Heinrichstrasse 26, 8010 Graz, Austria
e-mail: markus.reuter@uni-graz.at
M. Harzhauser
Á O. Mandic Á F. Ro¨gl Á A. Kroh
Natural History Museum Vienna,
Burgring 7, 1010 Vienna, Austria
M.-P. Aubry
Department of Geological Sciences, Rutgers University,
610 Taylor Road, Piscataway, NJ 08854-8066, USA
U. Wielandt-Schuster
Landesamt fu¨r Geologie, Rohstoffe und Bergbau
Baden-Wu¨rttemberg, Albertstrasse 5,
79104 Freiburg, Germany
A. Hamedani
Geology Department, Esfahan University,
81744 Esfahan, Iran
123
Int J Earth Sci (Geol Rundsch)
DOI 10.1007/s00531-007-0269-9
sedimentary cycle. Biostratigraphic studies on larger
foraminifers were carried out by Rahaghi (
1973
,
1976
,
1980)
, who assigned an Oligo-/Miocene age to the Qom
Fm. More recently, a paleoenvironmental reconstruction
based on microfacies analysis was attempted for the
f-Member (Okhravi and Amini
1998
). However, geological
research of the Qom Fm. mostly remained limited to the
Qom Basin and the f-Member because of economic
interests.
An Austrian/German cooperation-project, which aimed
at a paleobiogeographic reconstruction of the eastern
Mediterranean to western Indo-Pacific regions from the Late
Oligocene to Early Miocene, integrated data from faunal
analyses of the Qom Fm. from the Qom and Esfahan-Sirjan
basins (Harzhauser et al.
2002
; Harzhauser
2004
; Schuster
and Wielandt
1999
; Mandic
2000
). Within this project, basic
biostratigraphic data from the Qom Fm. outside the Qom
Basin were already published by Schuster and Wielandt
(
1999
). However, up to now no satisfactory stratigraphic
framework exists that allows a correlation of the Qom Fm.
between both basins, which is crucial for paleobiogeo-
graphic as well as for oil exploration aspects. The aim of this
study is therefore to bridge this gap by the development of a
high-resolution stratigraphy using integrated biostrati-
graphic and sequence stratigraphic approaches.
Geological setting and location of studied sections
The tectonic units of central Iran originated during sub-
duction and final collision of the African/Arabian Plate
with the Iranian Plate, the process of which already started
during the Mesozoic (Coleman-Sadd
1982
). An important
effect of the collision of these plates with far-reaching
paleobiogeographic and -oceanographic consequences was
the closure of the Tethyan Seaway (Fig.
2
) during the
Miocene. The so-called Terminal Tethyan Event (TTE)
marks the termination of migration of marine biota and
exchange of tropical waters between the eastern Mediter-
ranean and the western Indo-Pacific Tethys (Harzhauser
et al.
2007
). However, the exact timing of the TTE is still
debated. Adams et al. (
1983
) infer an Aquitanian age,
while several other authors proposed a Burdigalian age
(Ro¨gl and Steininger
1983
,
1984
; Ro¨gl
1997
,
1999
; Why-
brow
1984
; Robba
1986
; Harzhauser et al.
2002
). Jones
(
1999
) discussed intermittent episodes of separation of the
Eastern from the Western Tethys during Early and Middle
Miocene sea-level lowstands and a final closure not until
the end of the Middle Miocene. Another effect of the plate
collision was the formation of a fore-arc (Esfahan-Sirjan
Basin) and a back-arc basin (Qom Basin) on the Iranian
Plate at the north-eastern margin of the Tethyan Seaway
(Figs.
1
,
2
). These basins are separated by a volcanic arc
system (Fig.
1
), which developed during Eocene times
(Sto¨cklin and Setudehina
1991
). In both foreland basins the
marine sedimentation of the Qom Fm. began during the
Oligocene and continued until the Early Miocene (Rahaghi
1973
,
1976
,
1980)
. All sections presented in this paper
comprise deposits of the Qom Fm., which is lithostrati-
graphically defined as a marine succession bounded by the
underlying Lower Red Formation and the overlying Upper
Red Formation, both consisting of continental redbeds
(Sto¨cklin and Setudehina
1991
).
Within this study, two sections were investigated in the
Esfahan-Sirjan fore-arc basin (sections of Abadeh and
Zefreh) and two in the Qom back-arc basin (sections of
Qom and Chalheghareh) (Fig.
1
). The Esfahan-Sirjan fore-
arc basin strikes in a SE-NW direction about 550 km
parallel to the south-western margin of the Iranian Plate.
To the NE it is bounded by the Kuhrud Mountains, whereas
its south-western margin is formed by the Zagros Moun-
tains which are part of the Arabian Plate. Both investigated
sections are incomplete. Section Abadeh represents the
lower part of the Qom Fm. and has a thickness of 164 m,
while the totally 260 m thick Zefreh section is a repre-
sentative for its upper part and is situated in a more
marginal position of the basin than Abadeh. The section of
Abadeh is located 40 km NNE of the town Abadeh and can
be reached by a track which turns off from the main road to
Esfahan approximately 6 km NNW of Abadeh. This track
runs for about 40 km in N to NE direction until it reaches
some conspicuous E–W running hills. The section was
measured at the flank of the first hill NE of the track
(Fig.
1
d). The position of the base of the section is
31
°30.61
0
N, 52
°43.99
0
E. Section Zefreh is located 50 km
ENE of Esfahan, about 20 km north of the road from Es-
fahan to Nain, and west of the railroad track from Esfahan
to Kashan. The section is situated at the NE wing of an
anticline (Fig.
1
c) and is composed of two partial sections
(Zefreh A, Zefreh B). Zefreh A covers the stratigraphically
older part of the section. Its base is located at 32
°56.59
0
N,
52
°08.39
0
E. Zefreh B is located 500 m further east.
The Qom back-arc basin extends along the Elburz
Mountains from Semnan in the east to the Kuhrud Moun-
tains NW of Tehran, and from there about 650 km to the
south. The here measured section of Qom is located in the
type area of the Qom Fm. (Furrer and Soder
1955
) and near
the depocenter of the Qom Basin, where the formation
reaches a maximum thickness of about 1,000 m. The out-
crop is situated 100 km south of Tehran and c. 10 km SW
of the city of Qom at the southern flank of a large, E–W
oriented anticline with steeply inclined and overturned
beds (Figs.
1
a,
3
a). Its position (top of the section) is
34
°38.41
0
N, 50
°42.76
0
E. The Chalheghareh section has a
more nearshore position within the Qom Basin, which is
reflected in the lower thickness of the Qom Formation
Int J Earth Sci (Geol Rundsch)
123