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Abstract Ammonite biostratigraphy could be used in age determination and correlation of rock units in different sedimentary basins. Qumenjan section with 125 meters thickness is mainly formed by grey sandy limestone with grey and thick-bedded limestone intercalations. The study area is located in the eastern margin of the Lut Block. For a stratigraphical study of Lower–Upper Cretaceous deposits in southwestern of Qayen area, a stratigraphic section was selected and measured. Eight ammonites, including Anisoceras, Calycoceras, Hypoturrilites, Hysteroceras, Mantelliceras, Puzosia, and Scaphites genera and thirteen representative species were identified. Based on the identified assemblage fossils and comparison with international biozones, Hysteroceras orbignyi subzone for Late Albian age, Mantelliceras mantelli biozone for the lower part of Early Cenomanian age, Mantelliceras dixoni biozone for the upper part of Early Cenomanian age, and Turrilites costatus biozone for Middle Cenomanian age is suggested. According to identified genera and species a Late Albian–Middle Cenomanian age is assigned for ammonite bearing of the section. The first occurrence of Mantelliceras mantelli is taken as the base of Cenomanian. Compression of the identified ammonites with other basins shows that the east Iran basin was a part of Tethys Realm during late Albian–middle Cenomanian. Keywords:Biostratigraphy, Ammonite, Albian, Cenomanian, Qayen, East Iran. Introduction Ammonites are one of the best macrofossils for Cretaceous biostratigraphy. The Albian and Cenomanian ammonites of Kopet Dagh and Central Iran have been studied by numerous researchers such as Seyed-Emami and Aryai (1981), Seyed-Emami (1977), Seyed-Emami, (1982), Seyed-Emami et al. (1984), Immel and Seyed-Emami (1985), Seyed-Emami and Immel (1995, 1996), Immel et al. (1997), Mosavinia et al. (2007), Mosavinia and Wilmsen (2011), Mosavinia et al. (2014), and Wilmsen et al. (2015). The Cretaceous deposits have spread in the east of Iran and in Birjand and Qayen area. These deposits have different facies. The Cretaceous rocks include conglomerate and sandstone units in the base and then changed to limestones in Late Barremain to Aptian. During Albian–Cenomanian, the depth of the sedimentary basin increased and thin-bedded limestones, marly limestones, and marls were deposited. The Lower Cretaceous succession is composed of different rock units that are outcropped in the eastern margin of Lut Block. These deposits usually start with a basal conglomerate. “Orbitolinind Limestone” is an informal name that is used for a succession containing Orbitolina limestone and marl intercalations. Aptian–Cenomanian succession mostly is composed of detrital, marl, and carbonate beds most of which are biogenic sediments deposited in carbonate platforms. Upper Cretaceous deposits are mostly widespread in Maastrichtian (Stocklin et al. 1972; Fauvelet and Eftekharnezhad 1990). Flyschiod facies are also spread with Ophiolites in Upper Cretaceous (Aghanabati2004). One of the oldest studies conducted in the east of Iran is published by Clap (1940). Several geological and paleontological studies have been done by several researchers such as Stocklin et al. (1972), Tirrul et al. (1983), Fauvelet and Eftekharnezhad (1990), Berthiaux et al. (1991), Raisossadat and Skelton (2005), Babazadeh et al. (2010), Khazaei et al. (2011), Raisossadat et al. (2016), Sharifi et al. (2016), Motamedalshariati et al. (2016), Raisossadat and Noori (2016), Latifi et al. (2018), Raisossadat et al. (2017) and Zarei et al. (2019). Despite the above-mentioned studies , there still seems the need to do more studies in paleontological fields. Ammonites are known as useful fossil groups in age determination and are used as biostratigraphical and biozonation tool for the Cretaceous deposits. The aim of this study is to provide an ammonite biozonation and a short palaeobiogeographic discussion on the Cretaceous deposits of the study area. Material & Methods Based on the geological map and field observation, a stratigraphical section was selected and measured in the southwest of Qayen and in south of the Qumenjan Village. The geographical coordinates of the base of the section are 58° 52' 11" E 33° 32' 19" N. Sixteen rock and ammonite samples were collected. Ammonites were cleaned, covered with magnesium vapor and photographed. Collected specimens were identified. The collected samples were stored in the Department of Geology, University of Birjand. Discussion of Results & Conclusion The Qumenjan section with 125 meters thickness starts with a conglomerated bed at the base, and then continues with sandy limestones. The major part including a succession of grey limestone and argillaceous limestone intercalations. In this study, the following ammonites are identified: Anisoceras plicatile, Calycoceras gentoni, Calycoceras (Newboldiceras) asiaticum, Calycoceras sp., Hypoturrilites sp < em>., Hysteroceras orbignyi, Mantelliceras dixoni, Mantelliceras saxbii, Mantelliceras mantelli, Mantelliceras cf. lymense, Puzosia (P.) sp., Scaphites sp. Based on reported microfauna (Ahrari 2009; Moloudi 2014) and identified ammonites a Late Aptian to Middle Cenomanian age is suggested for the section. Based on the identified ammonites, the following biozones is suggested for the studied section: Hysteroceras orbignyi subzone: this subzone is introduced as an index subzone for the Late Albian. Range of this zone is from the first occurrence of Hysteroceras orbignyi to the first occurrence of Mantelliceras mantelli. The associate ammonite is Puzosia sp. The thickness of this subzone is 25 meters. Mantelliceras mantelli Interval Zone: This zone is reported from south of the UK, France, Spain, and Portugal and south of Africa. Mantelliceras mantelli is discussed as index zone of Early Cenomanian. The range of this zone is from the first occurrence of Mantelliceras mantelli to the first occurrence of Mantelliceras dixoni. The associate ammonites are Hyphoplites cf. costosus, Hypoturrilites cf. gravesianus, Scaphites sp. The thickness of this subzone is 19 meters. Mantelliceras dixoni Interval Zone: This zone is an index zone for lower part of Middle Cenomanian. However, this zone could confirm Middle Cenomanian. The range of this zone is from the first occurrence of Mantelliceras dixoni to the first occurrence of Turrilites costatus. The associate ammonite is Mantelliceras cf. lymense. The thickness of this subzone is 14 meters. Turrilites costatus Interval Zone: This zone is introduced by Hancock (1991). Alabushev (1995) introduced it as a subzone. Wilmsen et al. (2007) mentioned Anisoceras plicatile and Turrilites costatus as index fossils for Acanthoceras rhotomagense Zone. Kennedy and Gale (2015) reported Calycoceras gentoni from Middle Cenomanian. Acanthoceras rhotomagense is reported as the index zone of Middle Cenomanian. In the studied section A. rhotomagense has not been reported. Therefore, based on the occurrence of Turrilites aff. costatus Zone, Middle Cenomanian age is suggested for the upper part of the section. The associate assemblages include Calycoceras (Newboldiceras) asiaticum, Calycoceras gentoni, Anisoceras plicatile and Calycoceras sp. Latitudinal and provincial control of ammonite faunas was common throughout the Mesozoic. Both the ranks (realm, province, etc.) and names have varied from author to author. Tectonic movements and sea-level changes (regressions and transgressions) caused seaways connecting basins to open marine or close and led to several distinct new basins or limitation of seaways and between marine basins. Thus, numerous sub-realms and provinces have been named. Three biogeographic realms existed during the Mesozoic; Boreal Realm embraced the Arctic basins and the seas extending southward from there over parts of North America, Northern Europe, and Siberia. The Boreal seas were largely landlocked but linked by narrow seaways to the Tethyan Realm. The Tethyan Realm includes low latitude areas such as Africa, the Pacific, the Middle East, and America, and centered on the Paleo-Tethys Ocean. An Austral Realm has also been proposed for high southerly latitudes (Stevens 1973). To study the palaeobiogeographic conditions of Upper Albian–Lower Cenomanian in eastern Iran, the ammonite fauna of the studied section was compared with other reported ammonites from different areas. The reported ammonites from east of Iran show affinity with those reported from Kopet Dagh, Central Iran, Europe, and USA. The absence of Scholenbachia that is an index genus of the Boreal Realm and the presence of some genera such as Anisoceras, Scaphites, Hypoturrilites, and Puzosia could suggest that the study area is a part of Tethys Realm. However, the presence of Mantelliceras could show the effects of the influence of Boreal. The analysis of the ammonite stratigraphic distribution in the selected section in east of Iran allowed us to establish the faunal succession for the Upper Albian–Middle Cenomanian in the region. Based on identified assemblage, the following biozones are suggested. Hysetroceras orbignyi subzone is suggested as index zone of Late Albian, Mantelliceras mantelli Zone could confirm lower part of Early Cenomanian, Mantelliceras dixoni Zone is known as the upper part of Early Cenomanian and Turrilites costatus Zone is suggested as Middle Cenomanian. Compression of the identified ammonites with other basins shows that the east Iran basin was a part of Tethys Realm during Late Albian–Middle Cenomanian.

Introduction The Kopet-Dagh sedimentary basin is located in north-east Iran, southern Turkmenistan and Afghanistan and is composed of Mesozoic and Cenozoic sedimentary successions. Fifteen formations have been introduced in the Kopet-Dagh Basin. The Cretaceous formations include Shurijeh, Zard, Tirgan, Sarcheshmeh, Sanganeh, Aitamir, Abderaz, Abtalkh, Neyzar and Kalat (Afshar-Harb 1994). Aitamir Formation is one of the main rock units in the Kopet-Dagh basin. This paper presents the biostratigraphic data obtained based on nannofossils from the upper part of the Aitamir Formation. In order to study calcareous nannofossils a stratigraphic section was chosen in northwest Kopet-Dagh. The measured section is located about 35 km west of Maraveh Tappeh city and near Cherli village at 37 50' N latitude and 55 31' E longitude. Based on foraminifera assemblage, Kalantari (1969) suggested Cenomanian age for the Aitamir Formation. Thereafter, Seyed-Emami (1980), Seyed-Emami and Aryai (1981), Seyed-Emami et al. (1984), Immel et al. (1997), Mosavinia et al. (2007) and Mosavinia and Wilmsen (2011), based on ammonites, reported a late Albian-middle Cenomanian age for this formation. Moreover, Moradi Salimi (2012), and Raisossadat et al. (2013) in the center and west of Kopet-Dagh, Sharifi et al. (2012) and Garmabi and Mosavinia (2012) in the east of Kopet-Dagh discussed the ammonite contents and paleobiogeography of ammonites in the Aitamir Formation. The calcareous nanoplanktons of the formation have been studied by Susani (2005), Mousazadeh (2005), Moheghy et al. (2014) and Mousavi et al. (2016a, b). In the measured section, the formation conformably overlies the Sanganeh Formation and underlies the Abderaz Formation. The lower sandstone member is 711 m, consists of glauconitic coarse to fine grained sandstones with some intercalation of silty sandstones while the upper shale member is 359 m, composed of green to greenish grey, grey shales and marlstone that changes to limestone beds of Abderaz Formation at the top. A total of 100 samples were collected from the section with a thickness of 1070 m. The preservation and abundance of calcareous nannofossils in the lower sandstone member of the Aitamir Formation is very rare and poor but in the upper shale member it is good and the most abundant nannofossils belong to this member. Thirty-five (35) samples were collected from the shale member and used for calcareous nannofossil studies. For detailed calcareous nannofossil examination, simple smear slides were prepared using standard procedures. Smear slides were made from the fresh surface of raw sediment samples. Prepared slides were studied by using a polarized microscope and photographed by a digital camera. Corel draw and Photoshop softwares were used for drawing charts and figures. Discussion and Conclusion The standard Upper Cretaceous calcareous nannofossil biozonation Sissingh (1977) (the CC zones), which was modified by Perch-Nielsen (1985) and UC biozonation of Burnett (1998) were used. This scheme largely resulted from the examination of potential stage-boundary sections. Both biozonations were applied to the data on the range-charts. The biostratigraphic studies of the shale member of the Aitamir Formation resulted to the identification of 23 genera and 32 species of calcareous nannofossils are as follows; Amphizygus megalosa, Broinsonia enormis, Calcicalathina alta, Corollithion kennedy, Cyclagelosphaera margerelii, Eiffellithus turriseiffelii, Eprolithus floralis, Gartnerago segmentatum, Haqius circumradiatus, Icrorhabdulus belgicus, Lithraphidites carniolensis, Manivitella pemmatoidea, Marthasterites furcatus, Microrhabdulus decorates, Prediscophaera intercisa, Prediscosphaera columnata, Quadrum gartneri, Radiolithus planus, Retecapsa angustiforata, Retecapsa crenulata, Rhagodiscus angustus, Rhagodiscus splendens, Stoverius achylosus, Tranolithus orionatus, Tranolithus phacelosus, Watznaueria barnesiae, Watznaueria biporta, Watznaueria fossacincta, Zeugrhabdotus fibuliformis, Zeughrabdotus diplogrammus, Zeugrhabdotus embergeri, Zeugrhabdotus xenotus. The following biozones are suggested based on Sissingh (1977) and Burnett (1998). According to the first occurrence and last occurrence of index species and fossil assemblages, three biozones of Sissingh (1977) Eiffellithus turriseiffelii Zone (CC9), Microrhabdulus decorates Zone (CC10) and Quadrum gartneri Zone (CC11) equivalent to biozones UC0-UC7 of Burnett (1998) are suggested. The identified nannofossils zones, could confirm a Late Albian to Early Turonian age for the shale member at the Cherli section in the north western Kopet-Dagh. The determined age is nearly equal with the age obtained by foraminifera (Motamedalshariati et al. 2012). The age of the uppermost part of the Aitamir and the lowest part of Abderaz formations is the Early Turonian. Therefore, it appears that the contact between the Aitamir and Abderaz formations conform and sedimentation was continuous. In the boundary, lithology transitionally changes from shale in the uppermost part of the Aitamir Formation to limestone in the lowest part of the Abderaz Formation. However, more studies are required on this boundary in the western part of the basin.

Introduction: One of the first works about Cretaceous deposits in eastern part of the Lut Block is done by Stocklin et al. (1972). They reported Orbitolina limestones in Shah Kuh area and Maasterichtian siliciclastic and limestone beds which have overlaid the older deposits with a gap. In geological maps of the east of Iran, Upper Cretaceous deposits have been reported (Berthiaux et al., 1990; Eftekharnejad, 1991; Berberian and Soheili, 1992; Alvai Naini, 1983; Guillou et al., 1981 that they have been mostly referred to shallow and relatively deep facies. Moreover, Gorgich (2002), Gorgich et al. (2009) and Motie (2010) reported Maastrichtian deposits in the east of Iran. The study area is located at Geological Quadrangle Map of Qayen (Berthiaux et al., 1990) and Geological Sheet Map of Roum (Shahidi et al., 2000). The measured section is geographically situated at 33o 05′ north latitude and 59o 02′ east longitude. Aims and Method: This paper aims to study lithostratigraphy, identification of foraminifera assemblage, age determination, and biostratigraphy and biozonation of the measured section. The authors hope this research lead to a better understanding of the regional geology and distribution of Cretaceous foraminifera that might describe the degree of lithostratigraphic and biostratigraphic precision. In this research 160 samples have been collected which 130 samples were cut and thin sections were prepared. The other samples were disaggregated in dilute H2O2 (10% vol.) and washed. The washed residues were dried and picked the isolated forams. Thin sections studied under Olympus microscope and the foraminifera were identified and photographed. The isolated forms were photographed with Scanning Electronic Microscope (SEM) device model XL30 Philips in Technical Faculty of Tehran University. Discussion and results (Lithostratigraphy and biostratigraphy): From point of view of lithostratigraphy, the lower contact of the succession is faulted and the sequence could be divided into two informal members. The lower member is formed by intercalation of marl, shaly marl, thin bedded limestone and sandstone. The upper member includes medium to thick bedded limestone, medium bedded sandy limestone that changes to red sandstone. Moreover, in the upper part medium bedded limestone and sandy limestone are predominant. The upper boundary with Eocene deposits is unconformable. In the lower member, the following assemblage is identified; Abathomphalus sp., Bolivinoides draco draco, Dentalina granti, Gavelinella sp., Globotruncanita conica, Globotruncana arca, Globotruncana sp., Globotruncanita stuarti, Heterohelix sp., Heterohelix globulosa, Marssonella turris, Neoflabellina cf. permutata, Pseudotextularia sp., Pseudotextularia elegans, Pseudotextularia nuttalli, Planomalina sp., Schackonia sp. The following assemblage is also recognised in the upper member; Bolivinita planate, Goupilloudina iranica, Goupilloudina shirazensis, Globotruncanita stuarti, Heterohelix globulosa, Iranites ornatus, Lepidorbitoides socialis, Lepidorbitoides sp., Nezzazzata sp., Orbitoides media, Omphalocyclus macroporus, Orbitoides tissoti, Orbitoides apiculata. Pseudorotalia persica, Pseudotextularia elegans, Sulcoperculina sp., Siderolites calcitrapoides, Sirtina sp., Textularid. Globigerinelloides sp., Globotruncanita stuarti, Iranites ornatus, Lepidorbitoides socialis, Lepidorbitoides sp., Nezzazzata sp., Omphalocyclus macroporus, Orbitoides media, Pseudorotalia persica. Above the deposits that attributed to Cretaceous with a basal conglomerate, there is a sequence that the following foraminifera are identified; Alveolina pasticillata, Alveolina leupoldi, Alveolina aragonensis, Alveolina aff. pisella Alveolina (Glomalveolina) primaeva, Alveolina aff. rutimeyeri, Alveolina (Glomalveolina) sp., Biloculina sp., Miscellanea aff. iranica, Miscellanea sp., Nummulites convexa, Nummulites cf. guettardi. Based on the identified benthic and palnktonic foraminifera, three biozones are suggested as follows 1- Globotruncanita stuarti Interval Zone: this biozone is defined by first appearance of Globotruncanita stuarti to first appearance of Bolivinoides draco draco. The foraminifera assemblage includes Neoflabellina cf. permutata, Pseudotextularia elegans, Gavelinella sp., Globotruncana arca, Marsonella turris. The Globotruncanita stuarti is not reported as an index foraminifera in previous presented biozonations, but is known as one of well known foraminifera of the Globotruncana havanensis and Globotruncana aegyptica biozones (Robaszynski & Caron 1995; Sliter 1989). A Late Campanian to Maastrichtian is attributed to Globotruncanita stuarti biozone (Darvishzadeh and Abdolalipour, 2009 ;Abdelghany, 2003; Bertle and Suttner, 2005). 2- Bolivinoides draco draco Interval Zone: this biozone is defined by first of Bolivinoides draco draco appearance to first appearance of Omphalocyclus macroporus. The assemblage fauna including Heterohelix globulosa, Heterohelix sp., Pseudotextularia nuttalli, Pseudotextularia sp., Globotruncanita conica, Dentalia granti, Schackonia sp., Planomalina sp. This biozone is comparable with Akimets et al. (1991), Beniamovski and Kopaevich (1998), Olfer’ev and Alekseev (2005) and Beniamovski (2011). A Maastrichtian age is suggested for this biozone. 3- Siderolites-Omphalocyclus Assemblage Zone: this biozone is correlateable with biozone number 37 (Wynd, 1965) and also is reported by Maghfori Moghaddam (2005). The assemblage fauna including Omphalocyclus macroporus, Orbitoides media, Siderolites calcitrapoides, Textularids, Nezzazzata sp., Lepidorbitoides socialis, Orbitoides tissoti, Orbitoides apiculata. Based on the previous works such as Mitchell (2005) from Jamaica, Rosales-Domingoes (1997) from Mexico and Abd-El-Gawad (2010) from United Arab Emirates, the suggested biozone is similar to the mentioned areas. A late Maastrichtian age is suggested for this biozone. A Late Campanian–Late Maastrichtian age is suggested for the measured section. Conclusion: In the studied area, the following foraminifera are reported for first time; Abathomphalus sp., Bolivinoides draco draco, Dentalina granti, Gavelinella sp., Globotruncanita conica, Globotruncana arca, Heterohelix globulosa, Marssonella turris, Neoflabellina cf. permutata, Pseudotextularia elegans, Pseudotextularia nuttalli, Goupilloudina iranica, Goupilloudina shirazensis, Orbitoides tissoti, Orbitoides apiculata, Pseudorotalia persica, Based on the identified assemblage fauna, three biozones including Globotruncanita stuarti Interval Zone, Bolivinoides draco draco Interval Zone and Siderolites-Omphalocyclus Assemblage Zone are suggested. The assemblage fauna confirms a Late Campanian-Maastrichtian age. Moreover, the following assemblage fauna including Alveolina pasticillata, Alveolina leupoldi, Alveolina aragonensis, Alveolina aff. pisella Alveolina (Glomalveolina) primaeva, Alveolina aff. rutimeyeri, Biloculina sp., Miscellanea aff. iranica, Miscellanea sp., Nummulites convexa, Nummulites cf. guettardi, are identified in the uppermost part of the succession. The assemblage suggests an Eocene age and therefore an unconformity is determined in the upper boundary of the sequence. It seems Laramid Orogenic phase has effected on facies changes at the east of Iran. It led gaps in the Upper Cretaceous deposits in some parts of the basin due to ophiolites emplacement. In adjacent areas, sedimentation continued in two flych-flychoid and calcareous facies. Presence of an unconformity in Cretaceous-Tertiary boundary is another result of Late Cretaceous Orogenic movements in the studied area that is proofed by basal conglomerate.