ORIGINAL PAPER

Biostratigraphy of Campanian—Maastrichtian sequences and faciesanalysis in Anaran and Samand Anticlines, Zagros, Iran

Samira Rahimi1 & Ali Reza Ashouri1 & Abbas Sadeghi2 & Abbas Ghaderi1

Received: 16 October 2019 /Accepted: 19 June 2020# Saudi Society for Geosciences 2020

AbstractGurpi Formation is an important sedimentary sequence in the Zagros area of southwest Iran. It provides effective cap rock at thetop of the Bangestan reservoirs and acts as a possible source for younger hydrocarbon reservoirs. Integrated facies analysis andpaleontological study of this formation are presented in two surface sections located on the Samand and Anaran anticlines ofLorestan Province. The formation has mainly composed of 203–298 m of argillaceous limestones with two clean limestonemembers of “Seymareh” and “Imam Hassan.” In the biostratigraphic part of this study, 51 species related to 16 genera ofplanktonic foraminifers in the Dareh Vorazan section and 44 species belong to 16 genera of planktonic foraminifera in Pahlehsection were distinguished. Accordingly, four biozones have been determined in the Dareh Vorazan and the Pahleh sectionswhich are Globotruncana aegyptiaca, Gansserina gansseri, Contusotruncana contusa, and Abathomphalus mayaroensis.Consequently, the Gurpi Formation has an age of Late Campanian–Late Maastrichtian. The location of the Cretaceous–Paleogene (K-Pg) boundary is detected at the top of this formation. Macroscopic field observations integrated with microscopicstudies have resulted in the recognition of four microfacies types that belong to open lagoon, shoal, proximal, and distal openmarine environments of shallow inner to deep basinal settings. Depositional facies and environments of studied sections areinterpreted in a regional depositional model.

Keywords GurpiFormation .Planktonicforaminifera .PahlehSection .DarehVorazanSection .Microfaciesanalysis .Lorestan .

Zagros

Introduction

The Gurpi Formation is one of the most importantlithostratigraphic units in the Zagros foreland basin becauseof its stratigraphic position and its significance in the petro-leum geology of Iran as source rock. The Gurpi Formation isextended in the Folded Zagros in the provinces of Khuzestan,Lorestan, and Fars. The Gurpi Formation has an open marineand deep sea sedimentation environment, which is why it is agood talent for biostratigraphy studies using planktonic fauna.

Studies conducted by some researchers on the GurpiFormation represent a Late Santonian–Thanetian age in dif-ferent parts of the Zagros area, based on different planktonicassemblages (e.g., James and Wynd 1965; Setudehnia 1972and 1978; Stoneley 1974 and 1990; Ghasemi-Nejad et al.2006; Darvishzadeh et al. 2007; Senemari and Azizi 2012;Beiranvand et al. 2013; Beiranvand and Zaghbib–Turki2014; Beiranvand et al. 2014; Zarei and Ghasemi-Nejad2014; Najafpour et al. 2014; Razmjooei et al. 2014;Zaghbib–Turki and Beiranvand 2017).

Despite the importance of this formation in the LorestanProvince, little is known about the depositional environmentand biostratigraphy of the Gurpi Formation. The main objec-tives of this study are the biostratigraphy based on the distri-bution of planktonic foraminifera and microfacies studies ofthe Gurpi Formation at the Dareh Vorazan and Pahleh sec-tions. Regarding the importance of this formation, its lateralvariation, and this fact that these sections have not been stud-ied yet, a precise biostratigraphic study was carried out atthese sections.

Responsible Editor: Beatriz Badenas

* Ali Reza Ashouriashouri@um.ac.ir

1 Department of Geology, Faculty of Science, Ferdowsi University ofMashhad, Mashhad, Iran

2 Department of Geology, Faculty of Earth Science, Shahid BeheshtiUniversity, Tehran, Iran

Arabian Journal of Geosciences (2020) 13:643 https://doi.org/10.1007/s12517-020-05593-3

Geological setting and stratigraphy

The Zagros folded and thrust belt (ZFTB) extends over an areaof 2000 km in the eastern margin of the Arabian Plate in thedirection of northwest-southeast from Turkey to the Strait ofHormuz (Mouthereau 2011). The Zagros Mountains in thesouthwest of Iran are one of the richest trenched or trustedbelts in the world. The emergence of sediments and trapswhich have produced and maintained hydrocarbons is relatedto the history of the northeast margin of the Arabian Plateevolution (Piryaei et al. 2010 and 2011).

Significant changes in its thickness and sedimentary faciesindicate a reaction to the complicated tectonics of the sheetmargin and the reactivity of basement faults (Sherkati andLetouzey 2004). After a sedimentary stopping from the latestJurassic, most parts of the Zagros area were covered with theCretaceous progressive sea. The Zagros Cretaceous rockshave not the same facies and are deposited in different sedi-mentary environments.

In the Lorestan Province (Fig. 1 a, b, c, d), theCampanian-Maastrichtian sequence includes a deep ma-rine depositional setting called the Gurpi Formation, whileon the northeast of Lorestan it becomes a shallow faciescalled Amiran Formation (Aghanabati 2004). In the Farsregion, Cretaceous outcrops indicate platform carbonates(Aghanabati 2004). So, it is accepted that during most ofthe Cretaceous, a deep marine (pelagic) environment wasdominated in the Lorestan that changes laterally into shal-low marine carbonate platforms, toward the Fars Provincein the southeast (Aghanabati 2004).

Due to the source nature and placement of the GurpiFormation between the Asmari and Bangestan reservoirs, ithas special importance (Aghanabati 2004). The name of thisformation has been derived from the Gurpi Mountain in thenorthwest of Masjed Soleyman County. At the type section,this formation includes 320 meters of marl and bluish-grayshales together with subordinate thin layers of clayey(argillaceous) limestone which overlies the limestones of theIlam Formation, along an erosional unconformity (Motie1994). This unconformity is accompanied by a weatheredzone consisting of iron oxide compositions. The upper bound-ary of the Gurpi Formation is marked at the base of purpleshale layers containing sand and silt that indicates the onset ofthe Pabdeh Formation (Motie 1994).

In most parts of Zagros, the Gurpi Formation includesbluish-gray shale and marls with some thin layers of clayey(argillaceous) limestone. In the Interior Fars, carbonate faciesof the Tarbur Formation substitute the Gurpi Formation. Thelower boundary of this with the Ilam Formation is gradual,and its upper contact is associated with various formations. InLorestan, the upper boundary of this formation with thePabdeh Formation is marked by purple shales. It isdiachronous in various parts of the Zagros area.

For example, in the Fars and Khuzestan provinces, thelower boundary of the Gurpi Formation is Santonian and itsupper boundary is Maastrichtian. In Lorestan, the underlyinglayers continue up to Campanian and the upper layers toPaleocene. The Gurpi Formation has two official membersof Seymareh and Imam Hassan and one unofficial memberof Mansouri Limestone (Motie 1994).

The Seymareh Member is a brown-colored limestonewhich contains Lopha spp. and has a shallow facies in com-parison with the Imam Hassan Member. The Imam HassanMember is a thick layer of argillaceous limestone and is prom-inent within the Gurpi Formation shales due to the greaterhardness. This member has been seen more in Lorestan andDezful Embayment. The Mansouri Member is a neritic lime-stone in the Gurpi Formation which is remarkable in the westof Khuzestan and fades toward the northeast (Fig. 2)

Materials and methods

This study is based on macroscopic field description of 510 mof Upper Cretaceous sequences (Gurpi Formation) in two sur-face sections (Pahleh and Dareh Vorazan) located on thenorthern flank of Anaran anticline and southern flank ofSamand anticline in Lorestan Province of Zagros, southwestIran (Figs. 3 and 4).

After preliminary studies and choosing appropriatestratigraphic sections, sampling was carried out systemat-ically in 1 m distances and shortened toward facies vari-ations and boundaries. In total, 412 hand samples weretaken from rock samples and sediments from these sec-tions for facies analysis and paleontological study.Sediments were washed on sieves 70, 120, and 250meshes, to extract fossils from sediments. After washing,samples were dried on sieves and put in special cells.Released fossils were studied by binocular firstly and thenby scanning electron microscope (SEM). Determinationand naming genera and species were done based onRobaszynski et al. (1984), Caron (1985), Loeblich andTappan (1988), and Premoli Silva and Verga (2004).The abbreviation of the names of genera is given inTable 1 and 2.

To characterize the depositional facies and environment,petrographic analyses (microfacies studies) of hand specimensand thin sections (245 thin sections) are integrated with themicroscopic image analysis, scanning electron microscopyanalyses, and quantitative analysis of all components in thestained (with Alizarin red S) thin sections. Facies analysis iscarried out using the standard models and microfacies descrip-tions (e.g., Wilson 1975; Flügel 2010) in addition to the mod-ified Dunham (1962) textural scheme by Embry and Klovan(1971).

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Study sections

Dareh Vorazan section

Dareh Vorazan section is located in the center of Samandanticline, 9 km from Anjireh village with geographic coordi-nates of 33° 01′ 43″ N; 47° 07′ 00″ E. The Gurpi Formationhas 203-m thickness in this section. The lower boundary with

the Ilam Formation is conformable with sharp lithology, andupper boundary with the Pabdeh Formation is gradational.

In terms of lithology, from the base to the top, it consists ofthe following units:

(1) Basal unit: 90-m thick consisting of alternating light grayargillaceous limestone and light gray limestone, mediumbedded

Fig. 1 (a) Map of Iran. (b)Geographical location of theLorestan Province in thesouthwest of Iran (Farzipour-Saein et al., 2009(. (c, d) studiedsections on the Anaran andSamand Anticlines

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(2) Seymareh member: 40-m thick consisting of light graylimestone which contains Lopha sp., thick bedded

(3) Middle unit: 20-cm thick consisting of dark gray marl,thin bedded

(4) Imam Hassan member: 22.80-m thick consisting ofwhite limestone, thick bedded

(5) Upper unit: 50-m thick consisting of alternating lightgray argillaceous limestone and dark gray argillaceouslimestone, thin bedded

In this study, 51 species related to 16 genera and 4 biozonesof planktonic foraminifers and 4 species related to 4 generaand 2 biozones of benthic foraminifers are recognized in theDareh Vorazan section.

Pahle section

Pahle section is located on the Anaran anticline, 16 kmfrom NW Bishe Deraz village with geographic coordinates32° 55′ 26.9″ N; 46° 49′ 44.8″ E. The Gurpi Formation has298-m thickness in this section. The lower boundary withthe Ilam Formation is comformable with sharp lithology

and upper boundary with the Pabdeh Formation isgradational.

In terms of lithology, from the base to the top, it consists ofthe following units:

(1) Basal unit: 111-m thick consisting of alternating lightgray argillaceous limestone and dark gray argillaceouslimestone, thin bedded

(2) Seymareh member: 106.50 m thick consisting of lightgray limestone which contains Lopha sp., medium tothick bedded

(3) Middle unit: 17.50 m thick consisting of light gray argil-laceous limestone, thin bedded

(4) Imam Hassan member: 31 m thick consisting of whitelimestone, thick bedded

(5) Upper unit: 32 m thick consisting of alternating lightgray argillaceous limestone and light gray limestone,thin bedded

In this section, 44 species belong to 16 genera of planktonicforaminifera and 5 species belong to 6 genera of benthic fora-minifera ranging in 4 planktonic foraminiferal biozones, and 2benthic foraminiferal biozones were distinguished.

Fig. 2 Upper Cretaceous to recent stratigraphy of the Zagros folded-thrust belt and Iranian margin of Persian Gulf (modified after James and Wynd1965)

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Fig. 3 (a) Field photographs ofthe Gurpi and Pabdeh formationsin the Dareh Vorazan section. (b)The Seymareh member. (c) TheImam Hassan member in theDareh Vorazan section

Fig. 4 (a) Field photographs ofthe Gurpi and Pabdeh formationsin the Pahleh section. (b)Seymareh member. (c) ImamHassan member in the Pahlehsection

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Results

Biostratigraphy

Planktonic foraminifera biozones

In this study, 55 species related to 20 genera and ranging in 4planktonic foraminiferal and 2 benthic foraminiferal biozonesare recognized in the Dareh Vorazan section and 51 speciesbelonging to 22 genera ranging in 4 planktonic foraminiferaland 2 benthic foraminiferal biozones in the Pahleh section.Distribution charts of these sections are presented in Figs. 5and 6. Plates of photomicrographs and SEMphotos of isolatedspecimens are provided as appendices (Plates 1,2,3 ,4 and 5).

Globotruncana aegyptiaca interval zone This zone whichcomprises of 15 m of the Gurpi Formation in the DarehVorazan section and 12 m in the Pahleh section is definedaccording to the appearance of Globotruncana aegyptiaca at

the base and the appearance ofGansserina gansseri at the topand is parallel to Gl. aegyptiaca biozone aged the end of LateCampanian (Premoli Silva and Verga 2004). Planktonic fora-minifers of this zone are as follows: Archaeoglobigerinablowi , Ar. cretacea , Contusotruncana fornicata ,C. plummerae, G. wiedenmayeri, Gl. aegyptiaca, Gl. arca,Gl. bulloides, Gl. hilli, Gl. lapparenti, Gl. linneiana, Gl.mariei Gl. orientalis, Gl. rosetta, Gl. sp., Gl. ventricosa,Globotruncanita stuarti, Ga. stuartiformis, Ga. sp.,Hetrohelix globulosa, H. navarroensis, H. planata,H. punctulata, H. sp., H. striata, Laeviheterohelix dentate,Macroglobigerinelloides alvarezi , M. multispinus ,M. prair ieh i l l ens i s , M. sp . , Muricohedberge l lamonmouthensis, Mu. sliteri, Mu. sp., Pseudotextulariaelegans, P. nuttalli, P. sp., Rugotruncana subcircumnodifer,Rugoglobigerina hexacamerata, Ra. rugosa, and Ra. sp..

Gansserina gansseri interval zone It places between the firstappearance of G. gansseri at the base and C. contusa on thetop covering 118 m of the Gurpi Formation in the DarehVorazan section and 206 m in the Pahleh section. Thisbiozone is parallel with theG. gansseri biozone aged the mostfinal part of Campanian-Maastrichtian (Premoli Silva andVerga 2004) including the following planktonic foraminifers:Ar. blowi, Ar. cretacea, Ar. sp., C. fornicata, C. patelliformis,C. plummerae, Contusotruncana sp., G. gansseri, Gl.aegyptiaca, Gl. arca, Gl. bulloides, Gl. falsostuarti, Gl. hilli,Gl. lapparenti, Gl. linneiana, Gl. mariei Gl. orientalis, Gl.rosetta, Gl. ventricosa, Gl. sp., Ga. angulata, Ga. conica,Ga. pettersi, Ga. stuarti, Ga. stuartiformis, Ga. sp.,Globotruncanella havanensis, Gla. minuta, H. globulosa,H. navarroensis, H. planata, H. punctulata, H. striata, H.sp., L. glabrans, M. alvarezi, M. bollii, M. messinae,M. multispinus, M. prairiehillensis, M. subcarinatus, M. sp.,Mu. holmdelensis, Mu. monmouthensis, Mu. sliteri, Mu. sp.,P. elegans, P. nuttalli, P. sp., Ra. hexacamerata, Ra.macrocephala, Ra. rugosa, Ra. sp., Ru. subcircumnodifer,and Ru. subpennyi.

Contusotruncana contusa/Racemiguembelina fructicosainterval zone This biozone is defined between the appear-ance of C. contusa at the base and Abathomphalusmayaroensis at the top which covers 20 m of the GurpiFormation in the Dareh Vorazan section and 8 m in thePahleh section and is equivalent of C. contusa andRacemiguembelina fructicosa biozones and aged Earlyto Late Maastrichtian (Premoli Silva and Verga 2004). Itincludes these planktonic foraminifers: Ar. blowi, Ar.cretacea, C. contusa, C. fornicata, C. patelliformis,C. plummerae, G. gansseri, G. wiedenmayeri, Gl.aegyptiaca, Gl. arca, Gl. bulloides, Gl. mariei, Gl.orientalis, Gla. havanensis, Ga. conica, Ga. stuartiformis,Ga. stuarti, H. globulosa, H. navarroensis, H. planata,

Table 1 Abbreviation of the names of genera

The full name of genera Abbreviation of the names of genera

Abathomphalus A

Archaeoglobigerina Ar

Contusotruncana C

Dorothya D

Gansserina G

Gavalinella Gv

Globotruncana Gl

Globotruncanella Gla

Globotruncanita Ga

Goupillaudina Go

Heterohelix H

Laeviheterohelix L

Lenticulina Ln

Macroglobigerinelloides M

Monolepidorbis Mo

Muricohedbergella Mu

Omphalucyclus O

Orbitoides Or

Pseudotextularia P

Racemiguembelina R

Rotorbinella Ro

Rugoglobigerina Ra

Rugotruncana Ru

Siderolites S

Sirtina Si

Trochammina T

Ventilabrella V

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H. punctulata , H. str iata , H. sp . , M. alvarezi ,M. subcarinatus, M. alvarezi, M. bollii, M. multispinus,M. prairiehillensis, M. sp., Mu. holmdelensis, Mu.monmou t h en s i s , P . e l e g an s , P . nu t t a l l i , Ra .hexacamerata, Ra. macrocephala, Ra. rugosa, and Ru.subcircumnodifer.

Abathomphalus mayaroensis Interval Zone It is definedbetween the appearance of A. mayaroensis species at thebase and extinction of Cretaceous planktonic foraminiferaat the top and covers 50 m of the Gurpi Formation in theDareh Vorazan section and 72 m in the Pahleh section.This biozone equals to A. mayaroensis biozone aged Late

Fig. 5 Distribution and planktonic foraminiferal zonation of the Gurpi Formation in the Dareh Vorazan section

Table 2 Summarized data of depositional facies and their characteristics in studied sections

Faciescode

Facies name Main allochems Sedimentaryfeatures

Depositionalsetting

Skeletal Non-skeletal

F1 Foraminifera (benthic andplanktonic) bioclastwackestone

Benthic foraminifera, echinoderm, rudist,bryozoan, coral, bivalves, algae, planktonicforaminifera

Peloid Bioturbation Open marinelagoon

F2 Benthic foraminifera bioclastpackstone to grainstone

Benthic foraminifera, echinoderm, algae,planktonic foraminifera, rudist, bryozoan,bivalve, coral

Peloid Cross-lamination Shoal

F3 Planktonic foraminiferawackestone to packstone

Planktonic foraminifera Glauconite,phosphatic grains,organic matter

Bioturbation,lamination

Outer ramp(proximal)

F4 Planktonic foraminiferamicrobioclast mudstone towackestone

Planktonic foraminifera Glauconite,phosphatic grains,organic matter

Bioturbation,lamination

Outer ramp(distal)

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Maastrichtian (Premoli Silva and Verga 2004) and con-t a i n s t h e f o l l ow i ng p l a nk t on i c f o r am in i f e r s :A. intermedius, A. mayaroensis, Ar. blowi, Ar. cretacea,C. contusa, C. fornicata, C. patelliformis, C. plummerae,C. sp., G. gansseri, G. wiedenmayeri, Gl. aegyptiaca, Gl.arca, Gl. bulloides, Gl. falsostuarti, Gl. hilli, Gl.lapparenti, Gl. linneiana, Gl. mariei, Gl. ventricosa, Gl.sp., Gla. havanensis, Gla. minuta, Ga. angulata, Ga.

conica, Ga. pettersi, Ga. stuartiformis, Ga. stuarti, Ga.sp . , H. globulosa , H. navarroensis , H. planata ,H. punctulata, H. striata, Hetrohelix sp., M. alvarezi,M . b o l l i i , M . m e s s i n a e , M . m u l t i s p i n u s ,M. prairiehillensis, M. sp., Mu. holmdelensis, Mu.monmouthensis, P. elegans, P. nuttalli, P. sp., Ra.hexacamerata, Ra. macrocephala, Ra. rugosa, Ra. sp.,Ru. subcircumnodifer, and Ventilabrella sp.

Fig. 6 Distribution and planktonic foraminiferal zonation of the Gurpi Formation in the Pahleh section

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Large benthic foraminifera biozones:

The G. gasseri biozone includes two regional biozones basedon large benthic foraminifera:

Monolepidorbis-Orbitoides assemblage zone This zonewhich envelops 28 m of the Gurpi Formation in the DarehVorazan section and 68 m in the Pahleh section is an assem-blage zone that is described by the first occurrence ofMonolepidorbis douvillei and Orbitoides sp. This biozone iscomparable with the assemblage biozone 36 byWynd (1695),and it is coeval with the middle part of G. gansseri biozone

aged the end of Late Campanian. Foraminifers of this zone areas follows:

Mo. douvillei, Or. media, Or. sp., Sirtina orbitoidiformis,Rotorbinella spp.

Omphalocyclus-Siderolites assemblage zone This zonewhich envelops 11 m of the Gurpi Formation in the DarehVorazan section and 36.5 m in the Pahleh section is an assem-blage zone that described the first occurrence ofOmphalocyclus macroprus and Siderolites calcitrapoides.This biozone is comparable with the assemblage biozone 37by Wynd (1695), and it is coeval with the upper part of

Plate 1 1a-c: Globotruncanaaegyptiaca (Nakkady 1950)—Dareh Vorazan section. 2a-c:Gansserina gansseri (Bolli1951)—Dareh Vorazan section.3a-c: Globotruncana bulloides(Vogler 1941)—Dareh Vorazansection. 4a-c: Contusotruncanafornicata (Plummer1931)—Dareh Vorazan section.5a-c: Globotruncana orientalis(El-Naggar 1966)—DarehVorazan section. 6a-c:Macroglobigerinelloidesmultispinus (Lalicker1948)—Dareh Vorazan section

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G. gansseri biozone aged Early Maastrichtian. Foraminifersof this zone are as follows: Goupillaudina iranica, Mo.douvillei, Or. media, Or. sp., Omphalocyclus macroprus,Ro. spp,. S. calcitrapoides, Si. orbitoidiformis.

Facies analysis

Facies analysis has resulted in the recognition of four faciestypes (microfacies) in the Gurpi Formation.

F1: Foraminifera (small benthic and planktonic)bioclastic wackestone

Description

This is a mud-dominated facies that includes a mixtureof small benthic (Dorothya sp., Trochammina sp.,Gavalinella sp., and Textularid) and planktonic forami-nifera (e.g., Mu. sp., H. sp.) and large skeletal grains(10–15%). Skeletal grains are mainly including echino-derms, rudists, bryozoan, corals, bivalves, and algalfragments (Fig. 7a, 7b). This microfacies has limestonelithology. Bioturbation and parallel lamination are im-portant features that have been recorded in the field

studies. Glauconite and phosphatic grains are also pres-ent as subordinate constituents.

Interpretation

Characteristics of this facies including mud-dominated tex-ture, lamination, and bioturbation all indicate its depositionin lower energy depositional setting. Other facies featuressuch as the presence of planktonic foraminifers point to anopen marine depositional setting.

The mixture of both benthic and planktonic biota and high-ly abraded skeletal fragments in a muddy matrix also refer to atextural inversion that is a common feature in open marinedepositional settings of carbonate platforms.

It could be considered as an equivalent of RMF-3(bioclastic wackestone and packstone with diverse, com-mon to abundant fossils, skeletal grains not worn, wholefossil preservation common) of ramp’s standardmicrofacies. It also corresponds with SMF-8 that repre-sents open marine lagoon setting in shelf-like carbonateplatforms (Flügel 2013). The similar facies is also report-ed from the Tarbur Formation as time equivalent of theGurpi Formation in various parts of the Zagros area (e.g.,Vaziri-Moghaddam et al. 2005; Amiri Bakhtiar et al.2011; Parham et al. 2017).

Plate 2 1a-c: Pseudotextulariaelegans (Rzehak, 1891)—Pahlehsection. 2a-c: Pseudotextularianuttalli (Voorvijk, 1937)—Pahleh section. 3a-c:Abathomphalus mayaroensis(Bolli 1951)—Pahleh section. 4a-c: Contusotruncana contusa(Cushman 1926)—Pahleh sec-tion. 5a-c: Ventilabrella sp.(Cushman 1928) —Pahleh sec-tion. 6a-c:Macroglobigerinelloidesprairiehillensis (Pessagno1967)—Pahleh section

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F2: Benthic foraminifera bioclastic packstone tograinstone

Description

This grain-supported facies (packstone to grainstone)contains both small and large benthic foraminifera (D.sp., Gv. sp., Lenticulina sp., Or. sp., Textularid andMiliolides) and skeletal debris, as its main constituents.Bioclasts largely include echinoderms; algae; rudists;and rare bryozoan, bivalves, and corals. This facieshas limestone lithology. Glauconite is the most impor-tant non-skeletal grain in this facies (Fig. 7c, 7d). Finecross lamination is the only notable sedimentary struc-ture recorded in this facies during field studies.Micritization and marine cementation are two notableearly diagenetic features. In many cases, frequent (up

to 40%) large bioclasts (>2 mm in diameter) are pres-ently yielding a rudstone texture.

Interpretation

Grain-dominated textures along with well-sorted, abradedand highly cemented fabrics indicate deposition in high-energy conditions. Facies of similar characteristics arecommonly found in shoal complexes developed in highenergy settings, around fair-weather wave base (FWWB),and storm wave base (SWB) in both old and recent car-bonate platforms (e.g. Harris et al. 2009; Flügel 2013). Itcan be considered as the equivalent of RMF7 (bioclasticpackstone with abundant echinoderm, bivalve, foramini-fer, and skeletal grains) and SMF10 (bioclastic packstonewith skeletal grains) of microfacies types of Flügel (2013)found in ramp and shelf carbonate platforms. The above-

Plate 3 1a-c: Globanomalina compressa (Plummer 1927)—Pahleh sec-tion. 2a-c: Globanomalina compressa (Plummer 1927)—Pahleh section.3a-c: Subbotina triloculinoides (Plummer 1927)—Pahleh section. 4a-c:

Parasubbotina pseudobulloides (Plummer 1927)—Dareh Vorazan sec-tion. 5a-c: Parasubbotina pseudobulloides (Plummer 1927)—DarehVorazan section

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Plate 4 1: Macroglobigerinelloides alvarezi (Eternod Olvera 1959)—Dareh Vorazan section. 2: Rugotruncana subcircumnodifer (Gandolfi1955)—Dareh Vorazan section. 3: Heterohelix globulosa (Ehrenberg1840)—Dareh Vorazan section. 4: Macroglobigerinelloidesprairiehillensis (Pessagno 1967)—Dareh Vorazan section. 5:Globotruncanella havanensis (Voorwijk 1937)—Dareh Vorazan section.6: Contusotruncana contusa (Cushman 1926)—Dareh Vorazan section.

7: Macroglobigerinelloides subcarinatus (Broennimann, 1952)—DarehVorazan section. 8: Abathomphalus mayaroensis (Bolli 1951)—DarehVorazan section. 9: Globotruncana hilli (Pessagno 1967)—Pahleh sec-tion. 10: Globotruncanita stuarti (de Lapparent 1918)—Pahleh section.11: Contusotruncana fornicata (Plummer 1931)—Pahleh section. 12:Gansserina gansseri (Bolli 1951)—Pahleh section

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mentioned facies are positioned in the middle ramp andopen marine shelf settings, respectively (see Flügel 2013,for more details). Here, because of their close associationwith deep marine, outer platform facies, they are consid-ered to have formed around storm wave base (SWB).

F3: Planktonic foraminifer wackestone to packstone

Description

This is mud- to grain-dominated facies that containsvarious amounts (15–45%) of planktonic foraminifera.Dominant planktonic foraminifera are including Gl. sp.,Ga. sp., Gla. sp., and some other genus. Laminationand bioturbation are important sedimentary structures

of this facies. Glauconite, phosphatic grains, pyrite,and organic matter are also recorded. It has argillaceouslimestone lithology (Fig. 7e, 7f).

Interpretation

Mud- to grain-dominated textures of this facies indicateits deposition in shallower settings, in comparison withthe F4. Frequent planktonic foraminifera and rareness ofshallow-water biota point to deep marine settings. Thepresence of glauconite also supports deep marine depo-sition under the reduction condition. This facies isequivalent of SMF-3 (wackestones with abundant plank-tonic foraminifera) and RMF-3 (bioclastic wackestonesand packstones with abundant skeletal grains and

Plate 5 1: Siderolitescalsitrapoides (Lemark, 1801)—Dareh Vorazan section. 2:Goupillaudina iranica (Rahaghi1976)—Dareh Vorazan section.3: Lepidorbitoides socialis(Leymerie 1851)—Pahleh sec-tion. 4: Orbitoides media (dArchiac 1837)—Dareh Vorazansection. 5: Omphalocyclusmacroprus (Lemark, 1801)—Dareh Vorazan section. 6:Monolepidorbis douvillei (Aster,1928)—Pahleh section

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planktonic foraminifers), which were attributed to thebasin and outer ramp settings, respectively. Based onthe described characteristics (i.e., higher grain’s frequen-cies and the presence of benthic fauna), depositionalsetting of these facies seems to be shallower than F4.

F4: Planktonic foraminifer microbioclast mudstone towackestone

Description

This is a grain- to mud-dominated facies in which planktonicforaminifera are dominant allochems (5–10%). The texture ofthis microfacies varies from mudstone to wackestone. Themain allochems of F3 are planktonic foraminifera includingGl. sp., Ga. sp., Gla. sp., and some other genera. Glauconite,

phosphatic grains, organic matter, and pyrite are also record-ed. Lamination and bioturbation are important sedimentarystructures of this facies. The lithology of this microfacies ismainly argillaceous limestone (Fig. 7g, 7h).

Interpretation

Mud-dominated texture (mudstone to wackestone) indicatesdeposition in a low energy environment. Frequent planktonicforaminifera and the absence of shallow-water biota point todeep marine settings. The presence of glauconite, phosphaticgrains and pyrite also supports deep marine deposition underreduction condition. This facies is equivalent of SMF-3(wackestones with abundant planktonic foraminifera) andRMF-5 (pelagic mudstones and wackestones with planktonic

Fig. 7 Microphotographs of theidentified microfacies. (a, b)Foraminifera (benthic andplanktonic) bioclast wackestone(F1), PPL. (c, d) Benthicforaminifera bioclast packstone tograinstone (F2), PPL. (e, f)Planktonic foraminiferawackestone to packstone (F3) ,PPL. (g, h) Planktonic foraminifermicrobioclast mudstone towackestone (F4), PPL. pf plank-tonic foraminifera, bf benthic fo-raminifera, ech echinoderm, brybryozoan, glc glauconite

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microfossil), which were attributed to the basin and outerramp settings, respectively.

Facies frequency analysis

A total of 245 thin section samples of the Gurpi Formationwere studied to characterize their sedimentological features.Frequency analysis of various depositional textures has re-vealed that F4 (planktonic foraminifera microbioclast mud-stone to wackestone) is the most common microfacies in thestudied sections (Fig. 8). It forms 65.78% of the total definedfacies of the Gurpi Formation in the Dareh Vorazan sectionand 61.70% of this formation in the Pahleh section. As de-scribed earlier, F4 was formed in Dareh Vorazan in distalouter ramp environment (Fig. 9).

Shallower marine depositional facies (i.e., F1, F2) have ahigher frequency in the Pahleh section, which is located in theAnaran anticline. Open marine lagoonal facies of F1 (forami-nifera bioclast wackestone) form nearly 6.38% of total faciesand high-energy facies of shoal setting (i.e., F2: benthic

foraminifera bioclast packstone to grainstone) has 27.65%frequency (see Fig. 8B).

In the Dareh Vorazan section, shallow marine carbonatefacies of F1 and F2 are less frequent than the Pahleh section.They are recorded to have a frequency of 5.26 and 13.15%,respectively (Fig. 8a).

Depositional model

Depositional facies and environments of the Gurpi Formationwere the subjects of some previous studies in various parts ofthe Zagros area. Bahrami (2009) has studied microfacies andsedimentary environments of the Gurpi Formation in the Farsarea. This formation has nearly 500-m thickness in his studiedsections (i.e., Tang-e-Zanjiran and Tang-e-Abolhiat), and adeep shelf or basinal setting was proposed based on its faciescharacteristics.

Zarei and Ghasemi-Nejad (2014) have investigated sedi-mentary and organic facies of this formation in the southwest

Fig. 8 Facies frequency analysisin the studied sections. (a) DarehVorazan section. (b) Pahlehsection

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of Zagros and concluded that it has been deposited in a distalouter ramp or basinal environment.

They have differentiated three microfacies which havea close correlation with identified facies in the LowerGurpi Formation of AZNS-103 well. Fereydoonpouret al. (2014) have studied biostratigraphy and sequencestratigraphy of the Gurpi Formation in Dehdasht areaand proposed a deep basinal setting, based on its faunalcontent. Fakour et al. (2015) were studied for depositionalfacies and sequences of the Gurpi Formation in AbadanPlain. They have distinguished ten microfacies in this for-mation, among which eight microfacies were attributed to

the outer ramp and two microfacies to the middle rampsettings.

In short facies analysis of the Gurpi Formation (includingSeymareh Imam and Hassan Member) in studied diverse sec-tions has revealed that this formation shows diverse faciesbelonging to various environments deposition, from open ma-rine to lagoonal one the open marine lagoon, bioclastic shoal,and proximal and distal deep-marine facies. The conceptualdepositional model for the studied interval is presented inFigure 8. It should be noted here that F1 is mainly related toImam Hassan Member has been deposited in an open marinelagoon, while F2 (related to Seymareh Member) has been

Fig. 9 Depositional model for the Gurpi Formation in the studiedsections. Accordingly, deposition of the formation has occurred in deepmarine settings of a carbonate platform including the outer platform and

basinal environments. Shallow marine facies of Seymareh and ImamHassan members were deposited on the basin margins and highs

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deposited in a shoal setting. F3 and F4 containing largeamounts and diverse planktonic foraminifera have been de-posited in proximal and distal deep-marine setting respective-ly (Figure 10).

Conclusions

The Gurpi Formation at the Dareh Vorazan section with thethickness of 203 m composing of limestone, argillaceouslimestone, and the thickness of the Gurpi Formation inPahleh section is 298 and consists mainly of argillaceous lime-stone and limestone.

The lower boundary with the Ilam Formation is conform-able with sharp lithology changes and the upper boundary isgradational with the Pabdeh Formation in both sections.

Through this study, 51 species related to 16 genera and 4biozones of planktonic foraminifers in Dareh Vorazan sectionand 44 species belong to 16 genera and 4 biozones of

planktonic foraminifera in Pahleh section were distinguishedwhich are as follows:

& Globotruncana aegyptica zone& Gansserina gansseri zone& Contusotruncana contusa zone& Abathomphalus mayaroensis zone

Also in this study, 4 species related to 4 genera and 2biozones of benthic foraminifers in Dareh Vorazan sectionand 5 species belong to 6 genera and 2 biozones of benthicforaminifera in Pahleh section were distinguished which are asfollows:

& Monolepidorbis-Orbitoides assemblage Zone& Omphalocyclus-Siderolites assemblage Zone

According to these biozones and fossil content, the age ofthe Gurpi Formation was determined in Late Campanian toLate Maastrichtian.

Fig. 10 Sedimentological logs ofthe Gurpi Formation in thestudied sections

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Based on the detailed field observation and petrography ofthe Gurpi Formation in two studied sections, 4 microfaciestypes have been identified which are as follows:

& F1: Foraminifera (small benthic and planktonic) bioclastwackestone

& F2: Benthic foraminifera bioclast packstone to grainstone& F3: Planktonic foraminifer wackestone to packstone& F4: Planktonic foraminifer microbioclast mudstone to

wackestone

These microfacies have been deposited in four facies beltsincluding open lagoon, shoal, proximal, and distal open ma-rine environment.

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