Paleobathymetry and paleoecology of colonial ...

Paleobathymetry and paleoecology of colonial corals from the Oligocene–early Miocene (?) Qom Formation (Dizlu area, central Iran) Mehdi Yazdi, Mahnaz Parvanenejad Shirazi, Amir Hossein Rahiminejad & Razieh Motavalipoor Carbonates and Evaporites ISSN 0891-2556 Carbonates Evaporites DOI 10.1007/s13146-012-0122-5

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Author's personal copy Carbonates Evaporites DOI 10.1007/s13146-012-0122-5

ORIGINAL ARTICLE

Paleobathymetry and paleoecology of colonial corals from the Oligocene–early Miocene (?) Qom Formation (Dizlu area, central Iran) Mehdi Yazdi • Mahnaz Parvanenejad Shirazi • Amir Hossein Rahiminejad • Razieh Motavalipoor

Accepted: 2 October 2012 Ó Springer-Verlag Berlin Heidelberg 2012

Abstract The scleractinian corals from the carbonate facies of the Oligocene–early Miocene (?) Qom Formation in Dizlu area (northern Isfahan), central Iran were described in three separate coral intervals. From the base to the top of the study carbonate sequence, the coral assemblages of the intervals include 1—Madracis, 2—Leptoseris– Stylophora and 3—Poritidae–Faviidae–Siderastreidae. The species identified within the carbonates are dominated by: Goniopora sp., Pachyseris sp., Madracis cf. ornate, Madracis sp., Montastraea parva, Solenastrea cf. desmoulinsi, Tarbellastraea reussiana, Stylophora sp., Siderastrea crenulata and Leptoseris sp. The identified colonial coral species were not colonizing through a strong carbonate reefal structure. Instead, they were distributed as sparse patches or building coral biostromal frameworks. The thin branching colonies of Madracis species and the second coral assemblage (Leptoseris–Stylophora) that is dominated by thin branching and thin platy colonial growth forms reflect deeper depths of a carbonate ramp with low light intensity within the lower photic zone in a depth range M. Yazdi Department of Geology, Faculty of Science, University of Isfahan, Isfahan, Iran e-mail: [email protected] M. P. Shirazi R. Motavalipoor Department of Geology, Payame Noor University, PO BOX 19395-3697, Tehran, Iran e-mail: [email protected] R. Motavalipoor e-mail: [email protected] A. H. Rahiminejad (&) Department of Geology, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran e-mail: [email protected]

of 19–35 m and a maximum flooding surface. The coral associations of the Poritidae–Faviidae–Siderastreidae assemblage are mainly composed of massive colonies indicating the upper photic zone with depth of less than 20 m and a higher energy water regime. The three coral assemblages reflect marine paleotemperature of 19–20° C, respectively. Keywords Central Iran Oligocene–early Miocene (?) Qom Formation Coral Paleobathymetry Paleoecology Colonial growth morphology

Introduction The Oligo–Miocene deposits of the Qom Formation in central Iran (Sto¨cklin and Setudehina 1991; Schuster and Wielandt 1999; Toraby 2003; Seyrafian and Toraby 2005; Reuter et al. 2009; Mohammadi et al. 2011) represent one of the typical carbonate dominated successions with the most abundant scleractinian coral communities distributed among the Cenozoic sedimentary basins of Iran. Most of the studies on scleractinian corals from the Iranian Cenozoic sedimentary basins were focused on the sediments of this Formation (Schuster and Wielandt 1999; Schuster 2002a, b; Toraby 2003; Reuter et al. 2009). The Oligo– Miocene carbonate ramp sediments of the Qom Formation were widely deposited in Qom and Isfahan–Sirjan basins in central Iran (Sto¨cklin and Setudehina 1991; Reuter et al. 2009; Mohammadi et al. 2011). Generally, the sedimentary succession of the Formation is composed of limestones, marls, deep carbonates, siliciclastic sediments and gypsum (Seyrafian and Toraby 2005; Mohammadi et al. 2011). The skeletal scleractinian coral assemblages comprise one of the dominant carbonate components of the Qom Formation

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Author's personal copy Carbonates Evaporites

that are widely considered in environmental interpretations such as salinity, paleo-depth, paleoclimate and paleotemperature (Brandano et al. 2010; Perrin and Bosellini 2012). These carbonate frameworks were formed as patches, reefal, back reefs or biohermal lithified structures. Several species of scleractinian coral fauna from the formation were described by Schuster and Wielandt (1999) from Abadeh, Qom and Chalheghareh regions (Table 1). Toraby (2003) and Reuter et al. (2009) also described some more scleractinian corals from western Ardestan (NE Isfahan), Zefreh (NE Isfahan) and Qom section (Table 1). The most common coral constituents of the Oligo–Miocene carbonate deposits of the Qom Formation in central Iran are dominated by: Porites, Goniopora, Tarbellastrea, Stylophora, Favites, Leptoseris and Montastraea (Table 1). Based on the studies of Schuster and Wielandt (1999), the number of coral diversity in central Iran varies in different areas. In Isfahan–Sirjan fore-arc zone, the coral components of Oligocene settings are composed of 32 genera and 45 species inhabitant of diverse paleoecosystems (Schuster and Wielandt 1999). In the Qom back arc zone, the coral assemblage comprises 13 genera and 15 species that were distributed as thin patches or separate intervals (Schuster and Wielandt 1999). This study is focused on the paleobathymetry and paleoecology of the carbonate sediments of the Oligocene–early Miocene (?) Qom Formation in northeastern Isfahan (Figs. 1, 2, 3) on the basis of some colonial coral assemblages.

Material and methodology The colonial coral specimens were gathered from three separate horizons with carbonates (Figs. 2, 3). The coral taxa were determined on the basis of the growth forms and the size of colonies in field section and also the systematic features of corallites in thin-sections, such as the number of septa, morphology and the size of calyx (in a transversal view). Stereo microscope Olympus SZX12 was used for the paleontology studies and taking microphotographs from 32 selected thin sections. Insalaco (1998)’s classification was used to classify the colonial morphologies and coral growth fabrics of the identified scleractinian corals.

Locality, stratigraphy and lithology of the study section In this research, the carbonate outcrops of the Qom Formation were measured in Dizlu area, located in 55 km of north eastern Isfahan (Fig. 1). The geography coordinates of the section are 33°00 12/600 N and 52°20 9/800 E. Terrestrial red clastics and continental sediments of the Lower red Formation and the Upper red Formation are the older and

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younger sedimentary successions deposited before and after the sedimentation of the carbonate settings of the Qom Formation. As a part of the Qom anticline, the study formation in northeastern Isfahan is situated near the NW–SE trending Qom-Zefreh fault along the Zagros main thrust. The secondary faults as well as the main QomZefreh fault formed horst and grabens and disturbed the sedimentary layers and beds in the area. In Dizlu area, there is a gap between the carbonate succession of the Qom Formation and its basal sediments that are Permian in age (Fig. 3). Also, at the top of the formation, Devonian– Permian deposits were thrusted over between the carbonates of the Qom Formation and the clay sediments of the Upper Red Formation (URF) and Plio-Pleistocene sediments by two thrust faults (Fig. 3). From the basal sediments of the Qom Formation towards the upper parts, the corals in this study are identified in three different assemblages including 1—Madracis, 2—Leptoseris–Stylophora and 3—Poritidae–Faviidae–Siderastreidae (Figs. 2, 3). The first marine sequence of the Qom Formation at the base of the study section comprises 18-m thick white cream sediments including clay, marl and intercalations of coral bearing limestone with larger oyster bivalves (occur in almost all parts of the sediments) in a micritic groundmass (Fig. 3). Planktonic foraminifers such as Globigerina spp. are also present in the upper parts of this marine sequence (Fig. 3). The first identified coral assemblage almost appears in the middle to upper parts of this sequence (Figs. 3) and is composed of thin branching colonies of Madracis sp. and Madracis cf. ornate (Fig. 4a) grew in a micritc matrix of a wackstone packstone facies (Fig. 4). In the outcrops of the study section, these species are distributed as small patches. These corals with such colonial growth morphologies form colonies with sparse pillarstone growth fabrics. The second coral assemblage (Leptoseris– Stylophora assemblage) (Figs.2, 3) within the marine succession of the Qom Formation consists of corals colonized in 20-m thick layer of grey limestone (Fig. 3) with a micritic groundmass. The coral fauna of this assemblage builds a biostromal structure. Sparse Globigerina and large benthic foraminifers with hyaline wall such as large Lepidocyclina sp. are the foraminifer constituents within the sediments. Austrotrilina sp. are also the other benthic foram species that are present in the lower parts of the limestone layer. The Leptoseris–Stylophora assemblage (Figs. 2, 3) comprises platy colonies of Leptoseris sp. (Fig. 4b) and colonies of Stylophora sp. with columnar thin branching colonial growth morphology (Fig. 4c, d). The assemblage of the coral species forms mixstone growth fabric within the limestones. The overlying layers are consisting of 2 m of clay, fossil bivalve (Pecten) and echinoid bearing limestones, red sandstones (1 m thick) and 5 m thick layer comprising brown breccia and

Author's personal copy Carbonates Evaporites Table 1 Statistics of coral communities from the carbonate settings of the Oligo–Miocene Qom Formation in central Iran (modified from Rahiminejad et al. 2011) Age

Studied areas

Coral taxa

Oligocene

Abadeh

Cricocyathus sp. (Quenstedt 1881)

Schuster and Wielandt (1999)

Astrangia sp. (Milne Edwards and Haime 1848) Favites insignis (Duncan 1880) Goniopora sp. (Blainville 1830) Hydnophora cf. insignis (Duncan 1880) Leptoseris sp. (Milne Edwards and Haime 1849) Montipora sp. (Blainville 1830) Placosmiliopsis multisinuosus (Michelin 1842) Stylophora thirsiformis (Michelotti 1847) Acanthastrea sp. (Milne Edwards and Haime 1848) Acropora sp. (Oken 1815) Antiguastrea sp. (Vaughan 1919) Astreopora cf. meneghiniana (D’Achiardi 1866) Astreopora sp. (Blainville 1830) Caulastrea sp. (Dana 1846) Hydnophora solidior (Duncan 1880) Montastraea sp. (Blainville 1830) Porites sp. (Link 1807) Stylocoenia taurinensis (Michelin 1842) Stylophora cf. italica (D’Achiardi 1866) Agathiphyllia (Reuss 1864) Early Miocene

Chalheghareh and Qom

Acanthastrea sp. (Milne Edwards and Haime 1848) Caulastrea sp. (Dana 1846)

Schuster and Wielandt (1999)

Favia sp.1 (Oken 1815) Goniopora sp. (Blainville 1830) Montastrea schweinfurthi (Felix 1884) Porites sp. (Link 1807) Stylophora sp. (Schweigger 1819) Tarbellastrea cf. chevalieri (Bosellini 1996) Oligo– Miocene

West of Ardestan, (notheatern Isfahan)

Antiguastrea lucasiana (Defrance 1826)

Toraby (2003)

Tarbellastraea sp. (Defrance 1826) Tarbellastrae profundata (Catullo 1856) Favites insignis (Duncan 1880) Montastraea sp. (Blainville 1830) Caulastraea pseudoflabellum (Catullo 1852) Acropora sp. (Oken 1815) Goniopora sp. (Blainville 1830)

Oligo– Miocene

Qom

Goniopora sp. (Blainville 1830) Porites sp. (Link 1807)

Reuter et al. (2009)

Oligo– Miocene

Zefreh (NE of Isfahan)

Tarbellastraea sp. (Defrance 1826)

Reuter et al. (2009)

Leptoseris sp. (Milne Edwards and Haime 1849) Porites sp. (Link 1807) Goniopora sp. (Blainville 1830)

limestones (Fig. 3). Hyaline large benthic forams such as Operculina sp. are also present in the limestones and clay sediments. A 10 m thick layer of clay and marls with calcareous intercalations containing fossil assemblages of

shallow marine bivalves and barnacles (such as Lofa and Balanus) and benthic foraminifers including Amphistegina sp. and Austrotrilina sp. was deposited in the upper beds (Fig. 3). Upper in the section, the third coral assemblage

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Fig. 1 The locality of the study section in Dizlu, northeastern Isfahan (modified from Mannani 2010)

Fig. 2 Field photos showing that the colonial corals identified in the three assemblages include 1—Madracis assemblage, 2—Leptoseris–Stylophora and 3—Poritidae–Faviidae– Siderastreidae from the base to the top of the Qom Formation

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Fig. 3 Stratigraphic column of the Oligocene–early Miocene (?) Qom Formation in Dizlu area showing that the coral associations are distributed in three different assemblages of 1—Madracis assemblage, 2—Leptoseris–Stylophora and 3—Poritidae–Faviidae–Siderastreidae

(Poritidae–Faviidae–Siderastreidae assemblage) in the study succession (Figs. 2, 3) occurs in a coral biostromal carbonate bed (35 m thick) comprising argillaceous limestone (Fig. 3). The faunal constituents of the sediments including are colonial corals, shallow marine brackish bivalve oysters (in the lower parts of the bed), hyaline benthic foraminifer such as Ammonia sp., porcelaneous benthic foraminifers including Pyrgo sp. (commonly in lower and middle parts of the argillaceous limestone bearing bed) and macro gastropods (Strombus sp.) at the end of the marine sequence. The Poritidae–Faviidae–Siderastreidae assemblage is populated by massive colonies of Solenastrea cf. desmoulinsi, Tarbellastraea reussiana, Montastraea parva, massive dome shaped colony of Goniopora sp., spherical massive colony of Siderastrea crenulata and Pachyseris sp. with encrusting colonial growth form (Figs. 5, 6). The massive coral colonies dominate the coral assemblage and constitute a domestone

growth fabric. In relation with the other coral assemblages, there is less abundant micrticic groundmass among the corallites. A 20-m thick sequence with clay and marl lithology comprises the upper parts and the last marine settings of the Qom Formation in Dizlu area (Fig. 3). The biotic assemblages within the sediments consist of bivalves (oysters), bryozoans, macro gastropods (Strombus sp.) and small benthic foraminifers with hyaline walls such as Elphidium sp.

Age dating of the Qom Formation in Dizlu area Generally, the biozonation and age dating of the Oligocene and early Miocene carbonate successions in the Zagros basin and the carbonate sediments of the Qom Formation in Central Iran, are commonly based on the biozones defined by Wynd (1965) and Adams and Bourgeois (1967)

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Fig. 4 The identified coral species from the deeper marine environment. a Transversal section views from the corallites of the branching colony of Madracis cf. ornate in a thin-section. b Thin platy colony of

Leptoseris sp. in a rock sample. c, d Columnar thin branching colony of Stylophora sp

(Daneshian and Ramezani Dana 2007; Seyrafian et al. 2011). The assemblage biozones introduced by Laursen et al. (2009) and Van Buchem et al. (2010) can also be used for biozonation and age dating of the Qom Formation in Central Iran. In the study section, two biozones were determined in the lower and middle parts of the Qom Formation (Fig. 3). In the upper parts of the first marine sequence (18-m thick layer of clay, marl and intercalations of coral bearing limestone) of the formation, the first biozone is defined by the planktonic foraminiferal assemblage of Globigerina species (Fig. 3). This biozone is correlated with the Globigerina spp. zone (zone 55) of Wynd (1965) which is Rupelian–Chattian in age (Wynd 1965). The second biozone is defined almost in the middle parts of the study formation (Fig. 3). This assemblage zone consists of Lepidocyclina sp. and Operculina sp. (Fig. 3) and can be an equivalent of the biozone 56 of Wynd (1965) (Lepidocyclina–Operculina–Ditrupa assemblage zone) or the Lepidocyclina–Operculina–Ditrupa assemblage zone of Laursen et al. 2009) and Van Buchem et al. (2010)According to the authors, this assemblage zone reflects a Rupelian–Chattian age (Wynd 1965; Laursen et al. 2009; Van Buchem et al. 2010). Based on the stratigraphy position of the marine layers within the formation

(Fig. 3), the uppermost parts of the Qom Formation above the Lepidocyclina–Operculina assemblage zone (Fig. 3) are Chattian and probably early Miocene (Aquitanian?) in age.

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Growth morphologies, paleobathymetry and paleoecology of the coral assemblages Generally, colonization and growth of Cenozoic scleractinian corals in marine environments depend on different ecological factors, including sedimentation rate, salinity, temperature, light penetration, lithofacies features of the substrate, water energy and turbidity (Dodd and Stanton 1990; Veron 1995; Riegl and Piller 2000; Vennin et al. 2004; Tsaparas and Marcopoulou-Diacantoni 2005; Bosellini and Perrin 2008). Depending on the coral colonial growth morphologies, different colonies of coral species grow in different depth zones (James and Ginsburg 1979; Chappell 1980). This results in development of different coral paleobathymetry zones (Graus and Macintyre 1976; Insalaco 1998; Vennin et al. 2004; Mateu-Vicens et al. 2008; Perrin and Kiessling 2010). In the deeper zones of carbonate platforms such as deeper reefal fronts and


Fig. 5 a Transversal section of Solenastrea cf. desmoulinsi. a The corallites are scattered in a micritic matrix. b Spherical massive colony of Siderastrea crenulata. c, d Tarbellastraea reussiana. c A

massive colony in a rock sample. d Transversal section view of the coral in a thin section

protected parts of marine lagoons, the colonial coral communities are dominated by thin branching growth forms. In a shallowing trend, between the deep and the shallow marine zones, substrates are mostly colonized by columnar to thick branching colonies. James (1984) and Pomar (1991) discussed that the foliaceous or platy colonies of some species of Porites are not adapted to deeper waters but are inhabitant of the shallower paleobathymetry zones, where the colonies are dominated by columnar to thick branching colonies (Vennin et al. 2004). Thin platy colonies of some coral species such as Leptoseris sp. and columnar branching colonies of Stylophora sp. colonize the deeper parts of reefal frameworks or carbonate platform environments with lower light intensity and a maximum flooding surface (McCall et al. 1994; Riegl and Piller1997; Schuster and Wielandt 1999) (Table 2). Coral communities with hemispherical, massive and domed-shaped (domal) colonies or patch reefs are adapted to the high to moderate energy shallow-water zones (Table 2) such as shallow back-reefal ecosystems, marine lagoons or reef mounds and form thick and resistant coral frameworks against the high energy sea waves (Vennin et al. 2004; Rahiminejad et al. 2011; Perrin and Bosellini 2012). Sparse small colonies of some corals such as Acanthastraea with mussid colonial growth morphologies

can hardly be assigned to a particular depth range (Vennin et al. 2004). It should also be noted that different species from a taxon may have diverse colonial growth morphologies and, therefore, they represent different bathymetry zones and environmental conditions (Jackson1979; Weil and Knowlton 1994) (Table 2). Thus, the distribution and abundance of different colonial morphologies of the identified corals within the marine sediments of the Qom Formation can be useful in paleobathymetry zonation and paleo-ecology interpretations (Table 2). The distribution of the identified coral assemblages within the carbonates of the Qom Formation in the study section is mainly controlled by paleodepth, hydrodynamic water energy and light intensity. From the base to the top of the marine sequence of the formation, a shallowing-upward cycle can be traced based on the appearance of the three identified coral assemblages (Figs. 2, 3). The deeper depth zone of the paleoenvironment is characterized by thin branching colonies of Madracis sp. and Madracis cf. ornate (scattered in a micritic groundmass) and the thin platy colonies of Leptoseris sp. and colonies of Stylophora sp. with columnar thin branching colonial morphology. These coral communities reflect the outer to middle ramp (or deeper slope), where the illumination and light intensity is reduced in the lower photic zone (19–35 m depth zone) (Table 2;

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Fig. 6 a, b Montastraea parva. a Massive colonial growth morphology of the coral. b Microphotograph of transverse section of the corallites. c Corallites of Goniopora sp. (with a massive colony) are

scattered in a micritic groundmass. d Pachyseris sp. with encrusting colonial growth form

Fig. 7). The colonization of thin branching Madracis in a micritic groundmass indicates low influx of fine grain siliciclastic sediments. The presence of Leptoseris–Stylophora coral community and the accompanying foraminifera assemblage of sparse Globigerina species and large benthic forams with hyaline wall such as large Lepidocyclina sp. is consistent with such deep condition of a carbonate platform indicating a maximum flooding surface (Schuster and Wielandt 1999). The occurrence of Lepidocyclina sp. indicates moderate to low energy water in a marine oligophotic–euphotic zone or lower photic zone restricted to storm-wave line at the top and the fair-weather line in the deeper parts (Geel 2000; Flu¨gel 2004; Renema 2006; Barattolo et al. 2007; Sadeghi et al. 2011). Such deep sedimentary and environmental condition was also described by Schuster and Wielandt (1999) on the basis of the same coral assemblage (Leptoseris–Stylophora) and foraminiferal contents from the Qom Formation in Abadeh section, southwestern Isfahan, Iran. The shallower upper parts of the shallowing-upward cycle within the study formation (Fig. 3) are characterized by Poritidae–Faviidae–Siderastreidae coral community. The most typical coral species (as coral patches) of this assemblage were very common in

the Oligo–Miocene shallow marine environments with less than 20 m in depth in central Iran (Schuster and Wielandt 1999; Schuster 2002a, b). The shallow marine sediments of the Qom Formation in the study section were mostly colonized by massive colonies of Solenastrea cf. desmoulinsi, Tarbellastraea reussiana, Montastraea parva, massive dome shaped colony of Goniopora sp., spherical massive corallums of Siderastrea crenulata and Pachyseris sp. with encrusting colonies (Figs. 5, 6). Such coral community, which is dominated by massive colonies, is representative of upper photic zone in a shallow depth (\20 m depth) (Table 2; Fig. 7). The occurrence of associated bivalve oysters, macro gastropods(Strombus sp.), porcelaneous benthic foraminifers including Pyrgo sp. and hyaline benthic foraminifer such as Ammonia sp. is also consistent with such nearshore environment, probably a back-reef ecosystem. The dominance of massive colonies and the poorly developed micrticic groundmass among the corallites were in response to high to moderate water energy turbulence and hydrodynamic sea wave energy (Sheppard 1982; Vennin et al. 2004; Pomar and Hallock 2007). The three identified coral assemblages also reflect water paleotemperature of 19–20° C, respectively (Bosellini and Perrin 2008).

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Author's personal copy Carbonates Evaporites Table 2 (a) Paleobathymetry and paleoecology of different Cenozoic scleractinian corals on the basis of their colonial growth morphologies (modified from Schuster and Wielandt 1999; Karabiyikoglu et al. Colonial growth morphology

2005; Rahiminejad et al. 2011), (b) Paleobathymetry and paleoecology details of the identified corals in the Qom Formation in the study section Depth related light zone

Water energy

(a) Colonial coral Stylophora

Columnar thin branching

Lower photic zone

Moderate

Leptoseris

Thin platy

Lower photic zone

Moderate

Tarbellastrea Porites

Massive, hemispherical or domal Domal, massive

Upper photic zone Upper photic zone

High–moderate High–moderate

Porites

Branching, delicate, meandroid, nodular or concentric

Lower photic to oligophotic zone

Moderate (high inputs of fine-grained clastics)

Favites

Massive, hemispherical or domal

Upper photic zone

High–moderate

Platygyra

Platy

Photic

Moderate

Montastraea cf. tchihatcheffi

Massive

Photic

High–moderate

Acropora

Thin branching

Lower photic to oligophotic zone

Moderate–low

(b) Colonial corals from the study section Stylophora

Columnar thin branching

Lower photic zone

Moderate

Lepsoseris

Thin platy

Lower photic zone

Moderate

Madracis cf. ornate

Thin branching

Lower photic zone

Moderate

Madracis sp. Tarbellastraea reussiana

Thin branching Massive

Lower photic zone Upper photic zone

Moderate High–moderate

Montastraea parva

Massive

Upper photic zone

High–moderate

Goniopora sp.

Massive dome shaped

Upper photic zone

High–moderate

Solenastrea cf. desmoulinsi

Massive

Upper photic zone

High–moderate

Siderastrea crenulata

Spherical massive

Upper photic zone

High–moderate

Pachyseris sp.

Encrusting

Upper photic zone

High–moderate

Fig. 7 A Schematic model of paleobathymetric distributions of the identified colonial corals in different light zones on the basis of different colonial growth morphologies

Conclusions The paleobathymetry and paleoecology details of the Oligocene–early Miocene (?) carbonate sediments of the Qom

Formation in Dizlu area (northeastern Isfahan), central Iran were interpreted on the basis of the scleractinian coral contents of the carbonate frameworks. The colonial coral fauna are represented by: Goniopora sp., Pachyseris sp.,

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Madracis cf. ornate, Madracis sp., Montastraea parva, Solenastrea cf. desmoulinsi, Tarbellastraea reussiana, Siderastrea crenulata, Stylophora sp. and Leptoseris sp. Three coral assemblages of 1—Madracis, 2—Leptoseris– Stylophora and 3—Poritidae–Faviidae–Siderastreidae are characterized by these coral species. A shallow tropical– subtropical marine paleoenvironment is interpreted from the coral associations. In the deeper parts (19–35 m) of a carbonate ramp in the lower photic zone with low light condition, the substrate was colonized by thin branching colonies of Madracis, columnar thin branching colonies of Stylophora sp. and thin platy colonies of Leptoseris sp., reflecting a maximum flooding surface. The distribution of the corals in a micritic groundmass suggests that the colonies grew in an environment with low turbulence turbidity. The Shallower parts (\20 m) of the carbonate ramp with higher energy and more light intensity in the upper photic zone are dominated by massive colonial corals from the Poritidae–Faviidae–Siderastreidae assemblage. Acknowledgments We hereby gratefully thank Prof. Ann Budd from the University of Iowa for her valuable helps in taxonomy identification of the coral species.

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