Geoscience Frontiers 5 (2014) 103e112

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China University of Geosciences (Beijing)

Geoscience Frontiers

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Research paper

Facies analysis and depositional environments of theOligoceneeMiocene Asmari Formation, Zagros Basin, Iran

Mohammad Sahraeyan a,*, Mohammad Bahrami b, Solmaz Arzaghi b

aDepartment of Geology, Khorasgan (Esfahan) Branch, Islamic Azad University, Esfahan, IranbDepartment of Geology, Fars Science and Research Branch, Islamic Azad University, Shiraz, Iran

a r t i c l e i n f o

Article history:Received 18 January 2013Received in revised form14 March 2013Accepted 25 March 2013Available online 8 April 2013

Keywords:Asmari FormationTang-e-LendehBenthic foraminiferaCarbonate ramp

* Corresponding author. 7419714454, Hejrat No. 11, JaTel.: þ98 9177915850.E-mail address: m.sahraeyan@yahoo.com (M. Sahraey

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a b s t r a c t

The Asmari Formation (a giant hydrocarbon reservoir) is a thick carbonate sequence of the OligoceneeMiocene in the Zagros Basin, southwest of Iran. This formation is exposed at Tang-e-Lendeh in the Farsinterior zone with a thickness of 190 m comprising medium and thick to massive bedded carbonates. Theage of the Asmari Formation in the study area is the late Oligocene (Chattian)eearlyMiocene (Burdigalian).Ten microfacies are defined, characterizing a gradual shallowing upward trend; the related environmentsare as follows: open marine (MF 8e10), restricted lagoon (MF 6e7), shoal (MF 3e5), lagoon (MF 2), andtidal flat (MF 1). Based on the environmental interpretations, a homoclinal ramp consisting of inner andmiddle parts prevails. MF 3e7 are characterized by the occurrence of large and small porcelaneous benthicforaminifera representing a shallow-water setting of an inner ramp, influenced by wave and tidal pro-cesses. MF 8e10, with large particles of coral and algae, represent a deeper fair weather wave base of amiddle ramp setting.

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1. Introduction

The Asmari Formation (a giant hydrocarbon reservoir) is a thickcarbonate sequence of the OligoceneeMiocene in the Zagros Basin,southwest of Iran. Lithologically, the Asmari Formation consists ofthin, medium to thick andmassive carbonate layers. Some sandstonelayers (the Ahvaz Member) and anhydrite deposits (the KalhurMember) are also present. The Kalhur evaporite deposits in theLurestan Province and Ahvaz sandstone deposits in southwest DezfulEmbayment are two members of the Asmari Formation, but theAhvaz and Kalhur members are absent in this columnar section.

The Asmari Formation at the type section consists of 314 m oflimestones, dolomitic limestones and argillaceous limestones(Motiei, 1994). The Asmari Formation, at its type section, was

hrom City, Fars Province, Iran.

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deposited during the late Oligocene (Rupelian)eearly Miocene(Burdigalian). The base of the Asmari Formation varies in age. Forinstance, toward the coastal Fars area, it is mainly Rupelian while inthe Dezful Embayment; it ranges from Rupelian to Chattian (Motiei,1994). The top of the Asmari Formation, mostly Burdigalian in age,remains constant, but toward the coastal and interior Fars, it isChattian.

Since there are not any studies on the facies analysis anddepositional environments of the Asmari Formation in the Tang-e-Lendeh outcrop or the related reports are not available, so the mainobjectives of this paper are (1) to describe and interpret themicrofacies of deposits of the Asmari Formation and (2) to describeand interpret the depositional environments represented by theAsmari Formation.

2. Geological setting

The Zagros Basin is composed of a thick sedimentary sequencethat covers the Precambrian basement formed during the Pan-African orogeny (Al-Husseini, 2000). The total thickness of thesedimentary column deposited above the Neoproterozoic Hormuzsalt before the Neogene Zagros folding can reach over 8e10 km(Alavi, 2004; Sherkati and Letouzey, 2004). The Zagros Basin hasevolved through a number of different tectonic settings since the

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M. Sahraeyan et al. / Geoscience Frontiers 5 (2014) 103e112104

end of Precambrian. The basin was part of the stable Gondwanasupercontinent in the Paleozoic, a passive margin in the Mesozoic,and it became a convergent orogen in the Cenozoic (Bahroudi andKoyi, 2004; Sahraeyan and Bahrami, 2012a, b, c).

During the Paleozoic, Iran, Turkey and the Arabian plate (whichnow has the Zagros Belt situated along its northeastern border)together with Afghanistan and India, made up the long, very wideand stable passive margin of Gondwana, which bordered the Paleo-Tethys Ocean to the north (Berberian and King, 1981). By the lateTriassic, the Neo-Tethys Ocean had opened up between Arabia(which included the present Zagros region as its northeasternmargin) and Iran, with two different sedimentary basins on bothsides of the ocean (Berberian and King, 1981).

The closure of the Neo-Tethys Basin, mostly during the lateCretaceous, was due to the convergence and northeast subductionof the Arabian Plate beneath the Iranian sub-plate (Berberian andKing, 1981; Stoneley, 1981; Beydoun et al., 1992; Berberian, 1995).The closure led to the emplacement of pieces of the Neo-Tethyanoceanic lithosphere (i.e., ophiolites) onto the northeastern marginof the Afro-Arabian plate (e.g., Babaie et al., 2001; Babaei et al.,2005; Babaie et al., 2006).

Continent-continent collision starting in the Cenozoic has led tothe formation of the Zagros Fold-Thrust Belt, continued shortening of

Figure 1. (A) General structural provinces of Iran (adapted from Heydari, 2008), and (B) six mstudy area is located in Fars Interior Zone.

the mountain range, and creation of the Zagros foreland basin. Thelate Cretaceous to Miocene rocks represent deposits of the forelandbasin prior to the Zagros Orogeny, and subsequent incorporation intothe colliding rock sequences. This sequence unconformably overliesJurassic to Upper Cretaceous rocks. Compressional folding beganduringor soon after thedepositionof theOligoceneeMioceneAsmariFormation (Sepehr and Cosgrove, 2004).

On the basis of lateral facies variations, the Zagros Fold-ThrustBelt is divided into different tectonostratigraphic domains thatfrom NW to SE are: the Lurestan Province or Western Zagros, theIzeh Zone and Dezful Embayment or Central Zagros, and finally FarsProvince or Eastern Zagros (Motiei, 1994) (Fig. 1). Also, fromsouthwest to northeast of the Zagros Basin the following zones aredistinguished: Zagros folded belt, fold and thrust belt, High Zagrosand crushed zone. The Zagros Basin is also one of the most prolificoil reservoirs in the Middle East. The study area (Tang-e-Lendeh) islocated in the northwestern part of the Fars Interior Zone close tothe Izeh Zone (Fig. 1B).

3. Study area and methodology

Tang-e-Lendeh outcrop is located about 2 km to the north ofLendeh City in Khuzestan Province. Several outcrop sections of the

ajor tectonostratigraphic domains of the Zagros Basin (adapted from Motiei, 1994). The

Figure 2. Geological map of the study area (after Fakhari, 1994).

M. Sahraeyan et al. / Geoscience Frontiers 5 (2014) 103e112 105

Asmari Formation were examined in the Tang-e-Lendeh. Detailedfield analysis and sampling were located in the study area at30�5804300 N/50�2602400 E (Fig. 2). The lower boundary of the AsmariFormation is exposed and underlain by the Pabdeh Formation andthe upper boundary is exposed and overlain by the GachsaranFormation (Fig. 3). 180 samples were taken and sampling was basedon field evidences and lithofacies changes. All thin sections werechecked under the microscope for biostratigraphy and faciesanalysis. The classification of carbonate rocks followed thenomenclature of Dunham (1962) and Embry and Klovan (1971).Facies definition was based on the microfacies characteristics,including depositional texture, grain size, grain composition, andfossil content (Flügel, 2004).

4. Previous works

The Asmari Formation was adopted after the Asmari anticlinelocated in the northern Dezful Embayment and was referred to asequence of CretaceouseEocene in age (Busk and Mayo, 1918). TheAsmari Formation was measured and defined as an Oligocenenummulitic limestone by Richardson (1924) and described byThomas (1948) as an OligoceneeMiocene carbonate interval. Jamesand Wynd (1965) summarized previous viewpoints and finallyformally defined the Asmari Formation. Recently, the studies ofbiostratigraphy, depositional environment and sequence stratig-raphy have been undertaken by Seyrafian et al. (1996), Seyrafian(2000), Seyrafian and Mojikhalifeh (2005), Vaziri-Moghaddamet al. (2006), Amirshahkarami et al. (2007) and Hakimzadeh and

Figure 3. Field photographs showing: (a) lower boundary of Asmari Formation with PabGachsaran Formation is also gradual.

Seyrafian (2008). Ehrenberg et al. (2007) and Laursen et al.(2009) examined the Asmari Formation based on Sr isotope stra-tigraphy and revised age ranges mostly for the lower and middleparts of the Asmari Formation. Moreover, salinity changes duringthe late Oligocene to early Miocene for deposition of the AsmariFormation have been described by Mossadegh et al. (2009).

5. Lithology

In the study area in Tang-e-Lendeh, the thickness of the AsmariFormation is 190 m. It is composed of thick to massive beddedlimestone in the lower part and medium bedded limestone in theupper part. According to this observation, we divided Asmari For-mation into two lithological units (Fig. 4).

5.1. Unit 1

This unit consists of 165 m thick to massive bedded, light creamto cream limestone (Fig. 4) and is mainly composed of foraminiferaand mollusks. This facies is classified as calcirudite to calcarenite(Grabau, 1913) and overlies the Pabdeh Formation.

5.2. Unit 2

This unit consists of 25-m thin to medium bedded, light yellowlimestone (Fig. 4) and is mainly composed of foraminifera, coralsand echinoderms. This facies is also classified as calcarenite tocalcilutite (Grabau, 1913) and underlies the Gachsaran Formation.

deh Formation, which is gradual, and (b) upper boundary of Asmari Formation with

Figure 4. Faunal distribution, biozonation and lithology of the Asmari Formation at Tang-e-Lendeh area.

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6. Biostratigraphy

The Asmari Formation studied byWynd (1965) and reviewed byAdams and Bourgeois (1967) can be assigned to three assemblagezones. Considering biozonation proposed by Laursen et al. (2009),the following foraminiferal assemblages were identified for thestudy area:

6.1. Assemblage 1

From the base upward to 34 m, Archaias asmaricus, Miogypsi-noides complanatus and Haplophragmium singeri are present. Thefaunal assemblage is time equivalent to the Archaias asmaricus-Archaias hensoni-M. complanatus assemblage zone of the Chattianage (Fig. 4).

6.2. Assemblage 2

This assemblage zone which is 101 m thick mainly consists ofPeneroplis farsensis, Peneroplis tomasi, Dendritina sp., and Peneroplisevelutus and corresponds toMiogypsina-Elphidium sp.14-P. farsensisassemblage zone of Aquitanian age (Fig. 4).

6.3. Assemblage 3

From 135 to 190 m, Borelis melo curdica and Dendritina rangi arepresent. This faunal assemblage is time equivalent to Borelis melocurdica-B. melo melo of the Burdigalian age (Fig. 4).

In the study area, the age of the Asmari Formation is lateOligocene (Chattian)eearly Miocene (Burdigalian).

7. Microfacies and sedimentary environments

Ten carbonate sedimentary facies were recognized for theAsmari Formation in the study area. These facies are related to fivedepositional settings (tidal flat, lagoon, high-energy shoal,restricted lagoon, and storm-influenced open marine) of inner andmiddle portions of a carbonate platform.

7.1. MF 1: fenestral dolomitic mudstone

Features such as fenestral fabric, evaporate molds, microbialfilaments, mud cracks, and anhydrite nodules in a dolomicritematrix are observed abundantly in this microfacies (Fig. 5a, b). Thisfacies has intensively been influenced by diagenetic processes.Comparing with modern carbonate environments such as PersianGulf (Friedman, 1995), this facies has been deposited in upper partsof tidal flats in a warm and arid region. This microfacies is equiv-alent to SMF 21 of Wilson (1975) and RMF 23 of Flügel (2004).

7.2. MF 2: mudstone

This facies is virtually devoid of bioclasts except for a few ofmiliolid foraminifera, a marked contrast from the other facies.Porosity in the form of solution-enhanced molds suggests thatthere may have been leached out during meteoric diagenesis. Earlycalcite spar is also indicative of the presence of prior allochemswhich have now recrystallized, but original fabrics are unidentifi-able. The matrix is predominantly muddy and no compaction-pressure solution features were observed in association with thisfacies (Fig. 5c,d). Pyrite staining occurs rarely, probably related to

Figure 5. Photomicrographs showing: (a) and (b) fenestral dolomitic mudstone (MF 1); (c) and (d) mudstone (MF 2); and (e) and (f) imperforate foraminiferal grainstone (MF 3).

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bacterial activity in a deep lagoonal environment where sedimen-tation rates are low (Sugden, 1963, 1966). This facies is interpretedas a lagoonal deposit based on the high mud content.

7.3. MF 3: imperforate foraminiferal grainstone

The main characteristic of this microfacies is the maximumdiversification of imperforate foraminifera in grain-supported tex-tures. Several genera of imperforate foraminifera (Miliolids, Heter-ostegina, and Amphistegina) have been recognized. Pellets, peloids,intraclasts, and fragments of bivalves, echinoids, bryozoans, gas-tropods, and red and green algae are also present. The grains are

poorly to medium sorted (Fig. 5e, f). Due to changes in the type ofallochems on some samples, this microfacies should be defined asbioclastic imperforate foraminiferal packstone/grainstone.

Grain-supported texture with an abundance of foraminifera,particles of corals and red algae suggest that a moderate to high-energy bottom current environment occurred (Fournier et al.,2004). These biota and grain-supported texture are interpreted ashaving been formed in high-energy sand shoals, located at theplatform margin, separating the open marine from the morerestrictedmarine environments (Amirshahkarami et al., 2007). Thisinterpretation is corroborated by the lack of foraminifers indicatingdeeper water environment (Fournier et al., 2004).

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7.4. MF 4: bioclastic grainstone

This microfacies is characterized by the abundance of bioclasts.Bioclasts of this microfacies belong to gastropods, brachiopods,green algae (such as Salpingoporella sp. and Angioporella sp.),benthic foraminifers (such as Textularia sp. and Praechrysalidinainfracretacea), and echinoderms. Peloids and ooids are subordinatecomponents (Fig. 6a, b). This microfacies is a biosparite according toFolk (1962). Good roundness of intraclasts indicates high-energyconditions. The presence of allochems in sparry calcite cementand the absence of micritic matrix points to high-energy

Figure 6. Photomicrographs showing: (a) and (b) bioclastic grainstone (MF 4); (c) and (dforaminifera (MF 6).

conditions. This microfacies is comparable to SMF 18 and RMF 26 ofWilson (1975) and Flügel (2004), respectively.

7.5. MF 5: ooid grainstone

This microfacies is characterized by a high abundance of ooidswith concentric structure. Subordinate bioclasts, intraclasts andaggregate grains are also present. Bioclasts of this microfaciesbelong to gastropods, echinoderms and benthic foraminifers(mainly Praechrysalidina infracretacea), and dasycladacean algae.Composite and bahamite ooids as well as ooids with bioclast nuclei

) ooid grainstone (MF 5); and (e) and (f) mudstone with porcelaneous imperforate

Figure 7. Photomicrographs showing porcelaneous imperforate foraminiferal packstone/wackestone (MF 7).

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are observed in this facies (Fig. 6c, d). This microfacies is anoosparite according to Folk (1962), and comparable to SMF 15 andRMF 29 of Wilson (1975) and Flügel (2004), respectively.

7.6. MF 6: mudstone with porcelaneous imperforate foraminifera

MF 6 consists of wackestone to packstone textures as well asporcelaneous foraminifera poor in miliolid Archaias, Dendritinaand Borelis. Also, debris of red algae, Textularia, small rotaliids andrare ostracod are presence (Fig. 6e, f). The present of porcelaneousimperforate foraminiferal tests may point to a depositional envi-ronment being slightly hypersaline. Such an assemblage isdescribed as being deposited in a shelf lagoon environment(Wilson, 1975; Flügel, 1982, 2004; Vaziri-Moghaddam et al., 2006;Brandano et al., 2010). The scarce appearance of fossils in lime-mudmatrix with low diversity suggests deposition in a restrictedshallow subtidal water and slow sedimentation rate (Wilson, 1975;Flügel, 1982; Wanas, 2008). To summarize, the prevalence ofporcelaneous foraminifera strongly suggests deposition in a pro-tected inner-shelf environment.

7.7. MF 7: porcelaneous imperforate foraminiferal packstone/wackestone

This facies is characterized by an association of the largerbenthic foraminifera (LBF). Subordinate fragments are typically

Figure 8. Photomicrographs showing echinoder

echinoid, bryozoa, and bivalve debris. Also, there is occasionaloccurrence of coralline red algae range facies and the bioclastperforate foraminiferal corallinacean packstone (Fig. 7).

High taxonomicdiversityof LBFwithperforatewalls, corallinaceae,echinoid, bryozoa,micritematrix and stratigraphic position representdeposition on a shallower slope environment (Amirshahkarami et al.,2007). Moreover, the porcelaneous imperforate foraminifers live in atropical-subtropical environment over a wide bathymetric range, butare particularly frequent between depths of 40 and 70 m (Hottinger,1983, 1997; Hallock and Glenn, 1986). This microfacies is equivalentto RMF 16 (Flügel, 2004).

7.8. MF 8: echinoderm red algal packstone/wackestone

This microfacies shows a low degree of grain selection and anintense bioturbation that notably modifies the original texture ofthe rock (Fig. 8a). In preserved zones, the elongated clasts areparallel to the stratification and they form flat or slightly obliquelamination (Fig. 8b). Abundance and diversity of bioclasts andpresence of stenohaline organisms (echinoderms) show thatsalinity was normal marine. By similar reasons we assume thatoxygenation was high (aerobic zone). Presence of echinoderm in-dicates a firm substrate (Racki and Balinski, 1981).

While echinoderms and red alga are ubiquitous in this section,their abundances are higher than elsewhere. Some echinodermsshow syntaxial calcite rim (Evamy and Shearman, 1965). On rare

m red algal packstone/wackestone (MF 8).

Figure 9. Photomicrographs showing: (a) algal coralline boundstone (MF 9), and (b) coral rudstone/floatstone (MF 10).

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occasions, red algae have been partially dolomitized. Miliolids, os-tracods, bivalve shells and serpulid tubes occur in small amount inthis facies. The matrix was observed to be both muddy and sparryin places, probably a function of the amount of dissolution andrecrystallization. Due to the high diversity and biomass of bioclastsin this facies, it is interpreted as having been deposited in a shallowopen marine setting.

7.9. MF 9: algal coralline boundstone

The major allochems of this facies are carbonated algae andcorals which are common along the whole section and the spacebetween them has been filled with micrite (Fig. 9a). Algae andcorals are among the reef creatures. Growing beside each othermakes peace between them and as a result, mud forms betweenthem and two separate decks are connected by mud and make amassive structure, named as boundstone microfacies and is inter-preted as indicating the presence of an open marine environmentsimilar to RMF 7 of Flügel (2004).

7.10. MF 10: coral rudstone/floatstone

Coral rudstone locally presents a lower density of bioclasts(floatstone) and shows many encrusted layers (laminar stroma-toporoids, bryozoans, cyanobacteria and algae). Tabulates reach to30%; they include fragments of thamnoporoids. Bryozoans andstromatoporoids are also common (mostly encrusting ones,sometimes present as fragments). Echinoderms, brachiopods, gas-tropods, ostracods, algae, and cyanobacteria occur too. Spaces be-tween clasts are occupied usually by micrite, but some zones showmoderate percentage of sparite. Spectrum and abundance of

Figure 10. Depositional model of the A

bioclasts is high. No grain selection has been observed, but longclasts are parallel to the stratification (Fig. 9b). The degree of frag-mentation and disarticulation is high. Fragmentation indicates highenergy, but dominance of micrite indicates that the high level ofenergy was not constant. Encrustations by stromatoporoids andbryozoans (and less frequently by algae and cyanobacteria) prob-ably occurred during calm phases (Kershaw and Brunton, 1999).Presence of those encrustations as well as large fragments of col-onies and more rarely colonies in growth position indicate thattransport was short or absent and fragmentation took place in thesame area where the corals grew. Presence of algae and cyano-bacteria shows a very shallow environment (Liebau, 1980). Thesubstrate was hard, appropriate for the attachment of diversecolonial organisms (Brett, 1988).

All features prove the development of a bioconstruction (e.g.reef) in an unstable environment where destructive processes werealso important. It was probably a patch reef in initial stage ofdevelopment, affected by periodical storms and deposited in anopen marine.

8. Facies association and depositional model

Based on the above-mentioned microfacies, stratigraphy andsedimentary analysis together with lithofacies distribution andgradual shallowing upward trend, a homoclinal ramp depositionalenvironment is suggested for the deposition of the Asmari For-mation at the study area (Fig. 10).

During the OligoeMiocene, distally steepened and homoclinalramps were widespread in the Mediterranean areas (Pedley, 1996).Distally steepened ramp was resulted from an increased accumu-lation of both in-situ gravel-sized skeletal components and finer-

smari Formation in Tang-e-Lendeh.

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grained sediments transported from the shallower euphotic zone(Brandano et al., 2010). In-place, the grainstone fabrics are wide-spread in the massive shoals of the rimmed shelf.

Due to features associated with distally steepened ramp andrimmed shelf are not present in the studied section, a homoclinalramp depositional setting is suggested. Carbonate ramp environ-ments are characterized by: (1) the inner ramp, between the uppershoreface and fairweather wave base, (2) the middle ramp, be-tween fairweather wave base and storm-wave base, and (3) theouter ramp, below normal storm-wave base down to the basinplain (Burchette and Wright, 1992). Based on the studied sedi-mentary facies, depositional environment (inner and middle por-tions of a carbonate ramp) is proposed for deposition of the AsmariFormation in this study area.

8.1. Inner ramp

Seven main microfacies (MF 1e7) are subjected to the lagoon,shoal, and restricted lagoon environments of an inner ramp setting.Bioclastic shoal facies (MF 4) isolated the inner from the middleramp.

Benthic imperforate foraminifera are present. Moreover, othercomponents of this setting are scattered coral and red algaetogether with sea grass meadows. The large porcelaneous forami-nifera types such as Archaias, Peneroplis, Dendritina and Borelis arepresent. The occurrence of Archaias and Peneroplis is typical ofrecent tropical and subtropical shallow-water environments (Lee,1990; Holzmann et al., 2001) and are characteristics of the upperpart of the upper photic zone (Brandano et al., 2009). Furthermore,these large porcelaneous foraminifera are also common fossils inthe Mesozoic and Cenozoic neritic sediments (Brandano et al.,2009). The small porcelaneous foraminifera types mainly domi-nated as the abundant miliolids. In addition, some larger hyalineforaminifera such as rare Heterostegina and Amphistegina wereobserved. The Heterostegina and Amphistegina genera are typicallyrepresentative of warm water environments (Reiss and Hottinger,1984) and show relatively high ecological tolerances (Langer andHottinger, 2000).

The scattered, thinly branching coral fragments representreduced water energy in the deepest part of the euphotic zone ofthe lagoonal environment (Schuster and Wielandt, 1999). Theforaminifera (Peneroplis and miliolids) assemblage of this facies istypical of shallow-water and illuminated habitats, where sea grassmeadows interfinger with adjacent unvegetated areas (Brandanoet al., 2010).

Consequently, the biotic association of the inner ramp in thisarea could have originated from tropical and subtropical shallowwaters (Lee, 1990; Holzmann et al., 2001; Heydari, 2008; Brandanoet al., 2009) in sea grass-dominated environments, as suggested bythe presence of epiphytic foraminifera such as Archaias, Peneroplisand Borelis (Brandano et al., 2010). Based on these microfacies, ashallow-water setting of an inner ramp influenced bywave and tideprocesses is suggested for the deposition in MF 1e7.

8.2. Middle ramp

Three main microfacies (MF 8e10) are subjected to an openmarine environment of a middle ramp. More common componentsof these facies are biota association, such as Heterostegina,Amphistegina, Neorotalia, Miogypsinoides, corals, algae, and scat-tered coral fragments. Heterostegina and Amphistegina are ofparticular ecological importance (Brandano and Corda, 2002).These organisms populated tropical to subtropical environmentsover a wide bathymetric range, but are particularly common be-tween depths of 40 and 70m (Hottinger, 1983, 1997). Moreover, the

red algae association with these larger foraminifera places themiddle ramp in an oligophotic (Brandano and Corda, 2002; Cordaand Brandano, 2003; Brandano et al., 2009, 2010) to mesophoticzone (Hottinger, 1997; Pomar, 2001).

The Miogypsinoides and Neorotalia in wackestone/packstone,boundstone, and rudstone/floatstone textural rock types areformed in an open marine environment under normal marinesalinity conditions, normal water circulation and medium hydro-dynamic energy (Geel, 2000). As a result, MF 8e10 of the AsmariFormation in the study area represents the tropical to subtropicalenvironments in an oligophotic to mesophotic zone of the middleramp setting. Furthermore, the presence of epiphytic porcelaneousforaminifera and encrusting forms correspond to a depositionwithin the photic zone, in a sea grass-dominated environment(Brandano et al., 2009, 2010). Due to the absence of these forami-nifera, a middle ramp setting with no vegetation is proposed.

9. Conclusions

A section of the late Oligocene (Chattian)eearly Miocene (Bur-digalian) Asmari Formation at the Tang-e-Lendeh in the ZagrosBasin, was measured, sampled and studied. To reconstruct thedepositional environment, we were focused on field observations,facies analysis and distribution of the foraminiferal contents. In thestudy area, the thickness of the Asmari Formation is 190 m. It iscomposed of thick to massive bedded limestone in the lower partand medium bedded limestone in the upper part. Based on thebiostratigraphy of the Asmari Formation, age of this formation islate Oligocene (Chattian)eearly Miocene (Burdigalian). Tenmicrofacies (fenestral dolomitic mudstone, mudstone, imperforateforaminiferal grainstone, bioclastic grainstone, ooid grainstone,mudstone with porcelaneous imperforate foraminifera, porcela-neous imperforate foraminiferal packstone/wackestone, echino-derm red algal packstone/wackestone, algal coralline boundstone,and coral rudstone/floatstone), characterizing a gradual shallowingupward trend, were identified. The related environments were tidalflat, lagoon, shoal, restricted lagoon, and open marine. Environ-mental interpretations show that an inner and middle parts of ahomoclinal ramp prevailed during the deposition of the AsmariFormation in the studied area.

Acknowledgments

The authors wish to thank the Islamic Azad University, Khor-asgan (Esfahan) Branch for the financial support and ProfessorM. Ghavidel-Syooki for his cooperation in this study. We also ex-press our gratitude to Dr. Yener Eyuboglu (Associate Editor ofGeoscience Frontiers), Dr. Dmitry A. Ruban and anonymous refereewho made precise reviews, which helped us in enhancement offinal version. We are also grateful to Prof. Warren D. Huff (Univer-sity of Cincinnati) for his comments on the style of the manuscript.

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