Fig. 1
Localities and
geological maps (modified from
Zahedi
1978
; Amidi
1983
;
Amidi and Zahedi
1991
; Emami
1991
) of the studied locations in
central Iran. The Esfahan-Sirjan
Basin and the Qom Basin are
highlighted in light gray and the
volcanic arc as a dark gray field
in the overview map. The
serrated line indicates the
Zagros thrust fault. Qom Basin:
a
Qom locality, b Chalheghareh
locality. Esfahan-Sirjan Basin: c
Zefreh locality, d Abadeh
locality
Int J Earth Sci (Geol Rundsch)
123
(340 m). It is located directly west of the road from Es-
fahan to Kashan, 45 km north of Natanz, and NW of the
small village Chalheghareh, where the Qom Fm. is exposed
in an anticline. The section was measured at the NE wing
(Figs.
1
b,
3
b) and the position of the base of the section is
33
°46.99
0
N, 51
°43.76
0
E.
Sedimentary facies
The numbers provided in the following descriptions and
interpretations of the studied sections refer to consecutively
numbered beds in Figs.
4
,
6
,
7
,
8
and
9
.
Abadeh section
The Abadeh section (Fig.
4
) starts with the contact between
reddish, continental conglomerates of the underlying
Lower Red Fm. and the overlying Qom Fm. Although the
contact is usually not exposed due to a cover of alluvial
scree, nummulitic limestones were found in small isolated
outcrops that are located slightly above the contact between
the Lower Red and Qom formations.
The base of the Qom Fm. (1–13) is dominated by brown,
gray and red marls, and by argillaceous limestones. Char-
acteristic for this part of the section are Nummulites mass
occurrences (Nummulites sublaevigatus) with abundant
Ophiomorpha burrows (e.g., 1, 13). In the upper part of this
unit, thin (0.1–0.3 m) beds of fine-grained, partly lami-
nated calcareous sandstones and grainstones occur that
alternate with thicker (0.25–3.1 m) beds of argillaceous
limestones and marls. Tests of larger foraminifers (Num-
mulites, Operculina, heterosteginids, Amphistegina) are
distributed in the marly package. Associated rich assem-
blages of smaller benthic foraminifers are dominated by
Almaena, Neoeponides, Rosalina, Nonion, Cibicidoides,
and Lobatula. Plankton is scarce. Solitary corals, bivalves
and gastropods (Turritella and cerithiopsids, see Harzhau-
ser
2004
) are co-occurring (solitary coral assemblage
sensu Schuster and Wielandt
1999
).
Upsection (14–19) a distinct shift in rock color from red/
brown to gray/green occurs, yet without significant changes
in lithology. Marly sediments continue to be present, con-
taining now lepidocyclinids for the first time [Lepidocyclina
(Eulepidina) formosoides, L. (E.) favosa, L. (Nephrolepidi-
na)
morgani-type]
and
small
turritellids.
Planktic
foraminifers are common and represented by Globigerina
praebulloides, Gg. ciperoensis, Gg. anguliofficinalis, Gg.
ouachitaensis, Globigerinella obesa, Paragloborotalia
pseudocontinuosa, Pgr. opima opima, Pgr. opima nana,
Globorotaloides testarugosus, Tenuitellinata angustium-
bilicata, Tenuitella insolita, T. gemma, and Cassigerinella
chipolensis.
Fig. 3
View of sections Qom and Chalheghareh in the Qom Basin.
a
Overturned beds in the upper segment of the Qom section. The
continental redbeds of the Upper Red Formation are topped by
bioclastic limestones of the f-Member forming a steep cliff. b Section
Chalheghareh at the NE wing of an anticline NW of the village
Chalheghareh (Ch). Person for scale (white circle)
Fig. 2
Late Oligocene paleogeography of the Tetyan Seaway and
adjacent regions (modified from Harzhauser and Piller
2007
)
Int J Earth Sci (Geol Rundsch)
123
A distinct coral framestone horizon follows (20), which
thins out laterally but is traceable for several hundreds
of meters. It is dominated by foliaceous (Leptoseris) and
thin branching forms (Stylophora) with minor numbers
of massive dome-shaped colonies (mostly meandroid
faviids; Leptoseris-Stylophora assemblage sensu Schuster
and Wielandt
1999
). Associated planktic foraminifers
belong to Pgr. opima opima, Gg. anguliofficinalis, Gg.
Fig. 4
Abadeh section. From
left to right consecutive
numbers of sampled beds,
texture, formation names, scale
in meters, lithological
succession, chronostratigraphy,
water depth trend, and number
of identified depositional
sequences. The legend applies
also for the measured sections
Zefreh, Qom and Chalheghareh
(Figs.
6
,
7
,
8
,
9
)
Int J Earth Sci (Geol Rundsch)
123
praebulloides, Gg. ciperoensis, Gg. ex gr. brevis, Globo-
rotaloides
testarugosus,
Cassigerinella
chipolensis,
Tenuitella munda, T. insolita, and Tenuitellinata angusti-
umbilicata. The coral horizon is topped by gray-green
calcareous marls and argillaceous limestones with abun-
dant branching bryozoans in the first meter (21–24).
A prominent, 2.3 m thick bed of calcareous sandstone,
covering
the
marl/argillaceous
limestone
succession,
exhibits Callianassa burrows at its top that are filled with
Nummulites tests (25). The above following argillaceous
limestones show intercalations of fine-grained sandstones
and frequently contain plant debris and Nummulites sub-
laevigatus (26–27). From bed 28 onwards, argillaceous
limestones and marls occur, which include scattered but in
situ, dome-shaped, colonial corals with diameters of up to
0.2 m (Porites-Faviidae assemblage sensu Schuster and
Wielandt
1999
) (28). The frequency and size of corals
(poritids, faviids) increases upsection and finally form a
succession of small patch reefs with lateral extensions of
30–40 m and maximum heights of 5–6 m (29–32). They
are dominated by large (max. 1.8 m length, 1 m height),
hemispherical coral heads (Porites, Favites, Diploastrea),
with minor contributions of thick branching (branch
diameter up to 8 cm) corals (Porites, Caulastrea). Some
Porites colonies form microatolls (Fig.
5
b). Associated
with the patch reefs are larger foraminifers [L. (E.) dilatata,
L. undulata, L. cf. marginata, Rotalia viennoti, Hetero-
stegina cf. praecursor, Operculina complanata, Borelis
pygmaea, Austrotrillina cf. striata, Archaias sp.] and gas-
tropods (characteristic are giant strombids and Diastoma,
see Harzhauser
2004
). Together with all other macrofossils,
corals disappear in beds 33–34. However, miliolid fora-
minifers become abundant in the prevailing marls (33–34).
A polymictic conglomerate with an erosional base tops
the coral bearing succession (35). It is only locally exposed
and composed of well-rounded boulders up to 25 cm
length. Laterally the conglomerate disappears and an
erosional surface terminates the patch reef-unit. It is cov-
ered by gray, green and brown marls, as well as by fine-
grained calcareous sandstones with intercalations of
coarse-grained sandstones and fine-grained conglomerates
(36–40). This part of the section is rich in mollusks.
Intercalated is a low-diversity, small-sized potamidid fauna
accompanied by abundant cerithids and small neritids (38)
(Fig.
10
a; Harzhauser
2004
). It is overlain by a highly
diverse mollusk coquina (41) with various bivalves (Ku-
phus
melitensis,
giant
subrhomboidal
lucinids,
and
Acropaia emiliae) and gastropods (giant strombids, ar-
chaeogastropods, and thick shelled Ampullinopsis) (Mandic
2000
; Harzhauser
2004
).
Upsection, the siliciclastic content decreases and nodu-
lar bioclastic limestones (packstones and floatstones) with
corallinaceans, foraminifers, mollusks, and bryozoans
occur, which show a thinning upward trend (42–43). Some
beds contain soritid and peneroplid foraminifers. Above
follows a marl unit with mass occurrence of lepidocycli-
nids (44; Fig.
5
a), and argillaceous limestones (45–48) that
are topped by a 200 m wide and up to 16 m thick suc-
cession of reefoidal limestones. The reef frameworks are
constructed by platy and dome-shaped corals, which are
encrusted by coralline red algae (Neogoniolithon, Spong-
ites) (49–52). The reef succession is overlain by a package
of marls containing larger foraminifers (lepidocyclinids,
Rotalia viennoti, Amphistegina, heterosteginids, operculi-
nids), delicate branching bryozoans, and articulated
pectinids (Amussiopecten labadyei; 53–54) (Fig.
10
e). A
well-bedded succession follows, comprising corallinacean
(Neogoniolithon) pack-, float-, grain- and rudstones with
Borelis cf. pygmaea, Austrotrillina sp., Gypsina squami-
formis, amphisteginids, lepidocyclinids, soritids, pene-
roplids, and heterosteginids (55–58). These bioclastic
limestones also include coral communities that show a
distinct succession. In the basal part, in situ, non-framework
forming coral communities composed of dome-shaped
Fig. 4
continued
Int J Earth Sci (Geol Rundsch)
123