in Jurassic and Cretaceous Stratigraphy

Earth Science Frontiers, Vol. 17, Special Issue, Aug. 2010 ISSN 1005-2321
Tithonian Ammonites Fauna from Koppeh Dagh, Northeastern Iran
76
M.R. Majidifard
Research Institute for Geosciences (Geological Survey of Iran), Meraj Ave., Azadi Sq., P.O.Box 13185-1494, Tehran, Iran
(E-mail: m_majidifard@yahoo.com; majidifard@gsi-iran.org)
In contrast to the 1722 m measured by Afshar
Harb (1994) 1556 m were measured here. The Chaman
Bid Formation mostly consists of alternations of grey
limestone, grey marly limestone (mudstone to
packstone) with pyrite, shale, argillaceous shale, and a
few levels of sandstones. According to the ammonite
fauna, the Chaman Bid Formation ranges from
the ?Bathonian to the Tithonian. At the type locality,
the formation has been subdivided, from base to top,
into seven members.
Some of the ammonite genera and species are
recorded from Iran for the first time, including
Phanerostephanus subsenex, Nothostephanus sp.,
Nannostephanus cf. subcomutus, Richterella richteri,
Pseudolissoceras zitteli, Glochiceras sp., Oxylenticeras
cf. lepidum.
Based on ammonites, the Chaman Bid Formation
ranges from the the ?Bathonian to Lower Tithonian in
Chaman Bid section.
Open-marine environments of the Chaman Bid
Formation was separated from the extensive shelf
lagoon by a rimmed platform margin. Their sediments
were deposited on the slope of the carbonate platform
and in the adjacent basin.
Introduction
Jurassic rocks are widely distributed and superbly
exposed in the Koppeh Dagh (northeastern Iran). Some
parts of the Middle Jurassic are characterized by a thick
siliciclastic succession (Kashafrud and Bashkalateh
formations), whereas the Upper Bathonian to Tithonian
rocks are predominantly carbonates, which represent a
platform, slope and basin system. The Chaman Bid
Formation in the Koppeh Dagh, is the scope of this
research.
In the last decades, many authors studied the
Middle and Upper Jurassic succession of Iran with
respect to micro- and macrofossils (e.g. Madani, 1977;
Afshar Harb, 1979, 1994; Seyed-Emami et al., 1994,
1996; Schairer et al., 1999; Hosseniun, 1996).
The Middle and Upper Jurassic sedimentary
successions of Koppeh Dagh in northeastern Iran com-
prise four formations; Kashafrud, Bashkalateh, Cha-
man Bid and Mozduran.
Biostratigraphy and lithostratigraphy
Kashafrud Formation
This formation consists of a sequence of dark
coloured turbiditic siliciclastics containing turbidites.
They mainly comprise shales, siliceous shales and
sandstones. This unit is widespread in the south-eastern
region of Koppeh Dagh (Madani, 1977; Afshar Harb,
1994, 1979; Hossinion, 1996). In the southwestern
Koppeh Dagh the Kashafrud Formation is not deve-
loped; its time-equivalent rock units are the Bash-
kalateh and Chaman Bid formations. The lower part of
the formation overlies with angular unconformity or
locally with a coarse-grained conglomerate of the
Triassic Aghdarband Group, Upper Permian ophiolites,
or the Mashhad Granite of Mid-Cimmerian origin. The
upper boundary of the formation is either a
disconformity, a tectonic contact, or a conformable
contact with the Chaman Bid and Mozduran formations
(Hossenion, 1996). The Kashafrud Formation
represents a turbidite facies forming at the suture of the
Iran Plate with the Turan Plate (Seyed-Emami et al.,
1994).
Bashkalateh Formation
The formation occurs mainly in the western
Koppeh Dagh (Afshar Harb, 1979, 1994). According to
Seyed-Emami et al., (2001), it is a fine-grained lateral
equivalent of the Kashafrud Formation.
Chaman Bid Formation
The Chaman Bid Formation consists of grey to
bluish, thin- to medium-bedded limestone with interca-
lations of marly shale and marl (Afshar Harb, 1979,
1994). At the type section (north of Chaman Bid
village), the formation attains a thickness of 1722 m.
The thickness varies and increases from east of Koppeh
Dagh towards the west. The Chaman Bid Formation
conformably overlies the Bashkalate Formation. Its
upper boundary with the Mozduran Formation is sharp.
Main sedimentary environments of the formation are
basin and continental slope. Afshar Harb (1994) as-
signed a Late Bajocian to Oxfordian age to the
formation, but recent studies (Schairer et al., 1999)
show that the formation may continue up to the
Tithonian.
Mozduran Formation
At the type section, the Mozduran Formation
consists of light-coloured thick-bedded limestones to
massive, porous dolomitic limestones and dolomite.
According to Afshar Harb (1979) the thickness of the
formation at the type section is about 420 m, but
towards the northeast, at Sirzar village, it reaches 1400
m (Stöcklin, 1972). At the type locality, the Mozduran
Formation comformably overlies the Kashafrud
Formation. According to Afshar Harb (1979) however,
the contact is a weathered surface. At some localities of
the Koppeh Dagh region, the Mozduran Formation has
a conformable contact with the Chaman Bid Formation.
The upper boundary of the Mozduran Formation with