فهرست مطالب فاطمه هادوی

The present study is the first study aimed at biostratigraphy based on calcareous nannoplankton that has been performed on all succession exposed from the Oligo-Miocene marine deposits (members a to f of the Qom Formation). The studied deposits are located in the middle part of the Central Iran Zone and more precisely in the Navab anticline (northeast of Kashan city), which has a thickness of 417 meters. Due to the location and expansion of all members in this section, it has been a very suitable area for biostratigraphic assessments comparable to world standard models. In this study, a total of 370 microscopic slides prepared from rock samples were studied to the determination of the calcareous nannoplankton and accurately separate world standard biological zones, which led to the identification of 72 species belonging to 18 genera of this valuable group of the planktonic micro-organisms. According to the identified index species, standard nannoplankton biozones of the NP25 and NN1-NN4 were separated from this surface section of the Qom Formation. In addition, the equivalent biozones such as CNO5-6, CNM1- CNM6 as well as zones and subzones CP19b, CN1a, b, c, CN2- CN3, which belonging to the newest biozonation patterns, were also separated in this study. Therefore, based on the geological time value of the separated biozones, the age of late Chattian to late Burdigalian-early Langhian was proposed for the Qom Formation in the Navab anticline section. In this study, for the first time, the important chronostratigraphic boundaries such as the Paleogene-Neogene system boundary (or Chattian-Aquitanian stage boundary) in the upper parts of sub-member "c1", the Aquitanian- Burdigalian stage boundary at the base of member "e" and Burdigalian- Langhian in the upper part of member "f", were disaggregated based on biostratigraphic criteria.

In this research biostratigraphy of Baghamshah Formation based on calcareous nannofossills in the kalshaneh section was investigated. This section is located in northwest of Tabas. Baghamshah Formation in this section with 505 m thickness mainly consists of green- gray marl, very thin bedded shale with intercalation of fine sandstone and brown limestone abundant of brachiopodae and pelecypodae fragments and gerrn marl with interbedded of nodular limestone. Lower boundry with Parvadeh Formation is comformable and upper boundry with Kamar-e- Mehdi Formation is also marked. The study of nannofossils has been led to the identification of 44 species and belonging to 22 genera. According to stratigraphy distribution of calcareous nannofossils, CC3-CC5 biozones of Sissingh (1977) were determined. Nannofossil biozones indicate lateValanginian- late Haterivian age for the Baghamshah Formation in the Kalshaneh section.

For biostratigraphic studies based on calcareous nannofossils, late Cretaceous deposits in the Basiran section (northwest of Nehbandan) with 137 m were sampled. This section consists of sandstone, marly limestone, conglomerate, and marl. Based on taxonomical studies 18 genus belong to 34 species of nannofossils were identified. According to the calcareous nannofossils identified in this section, the CC20, CC21, CC22, CC23, CC24, CC25 and CC26 biozones were determined for the studied thickness. Based on determined biozones, age of the studied sequence in this section late early Campanian to late Maastrichtian was suggested. For paleoecological studies about 300 species were counted in each sample and their percentages were determined. According to paleoecological studies, sedimentary basin of the investigated deposits has relatively warm temperatures and located in low latitude.

This research has studied calcareous nannofossils of the Baghamshah Formation in Tabas Block (eastern Iran). Calcareous nannofossils are one of the most important fossil groups for biostratigraphical analysis. The earliest paleontological studies on the Baghamshah Formation have focused on ammonites (e.g., Seyed-Emami et al. 1988, 1991, 1997, 2001, 2002; Wilmsen et al., 2009). Kallanxhi et al. (2016) have also considered this formation's ammonites and nannofossil contents. The current study is the first investigation of calcareous nannofossils of the Baghamshah Formation in the Kharvan section and aims to discuss the possibility of using the standard nannofossil zones for the Baghamshah Formation.

The Kharvan section with 239 meters thickness is located 40 km northeast of Tabas near the Kharvan village. The formation has lithologically consisted of green and gray shales and marls. Generally, 75 samples from the Baghamshah Formation have been taken. Samples were prepared via the smear slide method (Bown & Young, 1998). All nannofossils were photographed in both cross-polarized light (XPL) and (PPL) and identified using Perch-Nielsen (1985) and Bown & Young (1998).

46 species belonging to 26 genera were identified in the studied section. Amongst them, 38 species belong to 21 genera of nannoliths and coccoliths, and 8 species from 5 genera belong to Didemnid ascidian spicules. Didemnid ascidian spicules are organisms with soft bodies and rigid spicules, which carbonate-rich seawaters and coral reefs are suitable environments for their colonization (Varol, 2006). The most dominant genera from the Baghamshah Formation are Watznaueria and Nannoconus. Among the nannofossil species, Nannoconus steinmannii, Retecapsa angustiforata, Calcicalathina oblongata, Tubodiscus verenae, Lithraphidites bollii, Cruciellipsis cuvillieri, and Nannoconus abundans are index species, used for biozonation. The Biostratigraphic studies in the Baghamshah Formation is led to the identification of calcareous nannofossils biozones CC1 to CC5 of Sissingh (1977) in the Kharvan section. Determined biozones represent the age of the early Berriasian - late Hauterivian for the investigated strata in the Kharvan section

The nannofossil assemblages of the Baghamshah Formation in the Kharvan section have average to pretty good preservation. In this section, the presence of CC1 at the lower part of the Baghamshah Formation and the presence of CC5 at the upper part of the formation shows that the age of the Baghamshah Formation is Early Berriasian - Late Hauterivian in the Kharvan section.

Calcareous nannofossils are one of the most important groups used for oceanic sections biostratigraphy. This research has studied calcareous nannofossils of the deposits attributed to Oligo- Miocene in Lut Block (eastern Iran). Previous nannofossils studies on Paleogene and Neogene deposits of east Iran were done by Hadavi & Zohravi (2010); Jalili et al. (2017). The present research is another investigation of calcareous nannofossils in the Avich section. The studied section with 550 meters thickness is located in the southwest of Qayen city and the south of the Avich village. The lithology of the deposits consists of sandstones, argillitic limestone, and green marl with interbedded sandstone. This study aims to determine the calcareous nannofossil assemblages and discuss the possibility of applying the standard zonation and age determination.

In this study, 20 samples from the upper part of the deposits attributed to Eocene, 100 samples from the lower part of the deposits attributed to Oligo-Miocene, and 100 samples from the upper part of these deposits from the Avich section have been studied. Samples were prepared as a smear slide method (Bown & Young, 1998). The examination of nannofloras was performed at 2500x magnification. All images were taken in either cross-polarized light (XPL) or (PPL). All calcareous nannofossil specimens were identified by using the taxonomic schemes of Perch- Nielsen (1985) and Bown & Young (1998).

Calcareous nannoplanktons are widespread in the present oceans, from coastal areas to open ocean settings. They are suitable for biostratigraphical studies since they are abundant, planktonic, rapidly evolving, and largely cosmopolitan. Regarding calcareous nannofossils, 45 species belonging to 18 genera have been recognized at the studied interval in the Avich section. In the present samples, structures of the central area in many species such as Helicosphaera and Chiasmolithus; indicate the calcareous nannofossils in this section have medium to relatively low preservation. The most important identified species are Chiasmolithus oamaruensis, Isthmolithus recurvus, Discoaster druggii, Triquetrorhabdulus carinatus, Discoaster kugleri, Catinaster coalitus, and Discoaster hamatus. Some species belonging to Discoaster, Catinaster, Triquetrorhabdulus and Isthmolithus are existed from the lower part or upper part of the studied section. Other taxa such as Hughesiu, Coccolithus, Tetralithoides, Sphenolithus, and Helicosphaera are present in most samples.In the present study, Martini's standard calcareous nannofossil zonation (1971) was applied. In this zonation, the NP abbreviation represents Paleogene nannoplanktons (Nannoplankton Paleogene), and NN abbreviation means Neogene nannoplanktons (Nannoplankton Neogene). In this study, according to the first and last occurrences of marker species of nannofossils, two calcareous nannofossil biozones NP18 (Chiasmolithus oamaruensis Zone) and NP19 (Isthmolithus recurves Zone) in the upper part of Eocene deposits, NN2 (Discoaster druggii Zone) and NN3 (Sphenolithus belemnos Zone) biozones in the lower part of Miocene deposits, and NN7 (Discoaster kugleri Zone) and NN9 (Discoaster hamatus Zone) in the upper part of Miocene deposits were recognized.Calcareous nannoplankton zones, especially the presence of NP19 at the uppermost part of Eocene deposits and the presence of NN2 at the lowermost portion of Miocene deposits, indicate that the investigated boundary has the age of Priabonian – Aquitanian in this area. Other determined biozones represent the age of the Aquitanian-Tortonian for the studied deposits attributed to Oligo-Miocene in the Avich section. In this section, the absence of NP20-NN1 biozones may be due to the facies changes and the lack of calcareous nannofossils in sandstone rocks of the succession or the tectonic activities between the Eocene and Miocene deposits.

The nannofossil assemblages of the Oligo-Miocene deposits of the Avich section are relatively good in diversity with medium to relatively low preservation. Index calcareous nannofossils allowed us to infer the biozonation and record bioevents in these deposits. In this section, the presence of NN2 at the lower part of Miocene deposits and the presence of NN9 at the upper part of the studied deposits show that the investigated deposits are Aquitanian - Tortonian in age.

The Binaloud Mountains, with an almost eastern-western trend, is extended from the Jajarm area in the Northern Khorasan to the Torbat-e-Jam region. In the Binalud zone, Jurassic succession in many places covered Paleozoic rocks and metamorphic assemblages, known as Mashhad Phyllite. Chaman-Bid Formation is one of the most famous Jurassic deposits in the northeastern. The studied sequence in the Ghroneh section is located at 43 kilometers north of Neyshabur and northeast of Ghroneh village (580 45' 36'', 360 45' 05''), respectively contains siliciclastic rocks of Kashafrud Formation, shale, marl, limestone, and sandstone beds of Chaman-Bid Formation, and thick to massif limestones of the Mozduran Formation. Most paleontological studies on the Chaman-Bid Formation are done based on ammonites (Majidifard, 2003, 2008; Raoufian et al., 2011, 2014; Seyed- Emami et al., 2013, 2018), palynomorphs (Mafi et al., 2014a,b), and more recently nannofossils by Amani et al. (2016). Based on calcareous nannofossils, the Early Bajocian–Early Berriasian age was suggested for the mentioned deposits in the Ghroneh section. In the present study, for the first time, ostracods of the Chaman-Bid Formation have been investigated. The present study introduces the Chaman-Bid Formation ostracods and compares this fauna within the calcareous nannofossils biozones.

  The thickness of the Chaman-Bid Formation in the studied section is 715 meters and consists of shale, marl, and limestone, interbedded with some sandstone beds. Sixty-four samples of the Chaman-Bid Formation with intervals of 10 to 15 meters were collected. 300 grams of each sample were soaked in water and hydrogen peroxide for 24 hours and washed in 30 and 60 mesh sieves. The residue was dried, and all ostracods in each sample were separated. The ostracods were studied with a Zeiss ZH55 microscope at 40x magnification and photographed in scanning electron microscopy (SEM) at the central laboratory of the Ferdowsi University of Mashhad.

Ostracoda is one of the most valuable crustaceans in paleontological and paleoecological studies. The remains of these small and microscopic crustaceans are widely distributed through Phanerozoic, and individuals belonging to this subgroup are characterized by their particular morphological and physical characteristics (Van Morkhoven, 1963). In the present study, 45 genera and 59 species of Ostracoda have been identified in the Chaman-Bid Formation in the studied section. Previous studies of Ostracoda have been compared with ammonite zones. The current study is important since there are no reports on Iran's Jurassic ostracods. Therefore, introducing ostracods and determining their age range is a significant objective of this study; however, their preservation is relatively poor. The study of the Chaman-Bid Formation ostracods in the Ghroneh section led to identifying of 59 species belonging to 45 genera. For relative age dating in the present study, calcareous nannofossils have been used and identified ostracods correlated with them. These assemblages have been compared with 12 previously reported nannofossil zones from the Ghroneh section. Nannofossil zones (Amani et al., 2016) belong to NJ9 to Early CC1 and confirm the age of Early Bajocian to Berriasian for the discussed ostracod assemblages.

In this research, paleoecology of Baghmashah Formation in Rizu section based on calcareous nannoplanktons has been investigated. Baghmashah Formation is part of the Mago sedimentary mega sequence in the Tabas block that was located in the northern margin of the Neotethys Ocean in Jurassic-Cretaceous. The Baghmshah Formation in this section with 270m thickness mainly includes the alternation of green marl- shale with thin interlayers of calcareous sandstone. The study of calcareous nannofossils and index species of nannofossil indicates Berriasian- early Huterivian age for the Baghmashah Formation in this section. Investigation of the abundance of calcareous nannofossils in the studied section shows that the sedimentary basin of Baghmashah Formation in Rizu section located in low latitude with warm surface waters, and formation deposited in oligotrophic conditions with shallow environment.

In the present study, Baghamshah Formation in Baghdadeh section located in the eastern margin of Lut Block to biostratigraphic studies based on calcareous nannofossils was sampled. Thickness of Baghamshah Formation in this section is 253m and mainly contains of shale and marl. According to the paleontological studies, 43 nannofossil species belong to 20 genera with well to moderate preservation in Baghdadeh section were identified and photographed. Based on the index calcareous nannofossils and assemblages species, CC1-CC5 biozones of Sissingh (1977) were determined. According to determined biozones, age of the Baghamshah Formation in Baghdadeh section Early Berriasian to Early Barremian was suggested.

The Kopeh‍ Dagh sedimentary basin is located in the North and North East of Iran (Stöcklin & Setudehnia, 1991) and contains the most complete Cretaceous sediments (Darvishzadeh, 2010). Abtalkh Formation is has a maximum thickness in the East of Kopeh Dagh basin (Stöcklin & Setudehnia, 1991). The lithology of Abtalkh Formation mainly consists of light gray, blue to green shale, and siltstone. It conformably overlies the Abderaz Formation and the upper boundary is conformable with Neyzar Formation (Khosro-Tehrani, 2007). In this research, we aimed to present biostratigraphy of ostracods from Abtalkh Formation in the Babafaraji section.

The thickness of the Abtalkh Formation is 840 m in the Babafaraji section. In this study from Abtalkh Formation, 80 samples were collected every 10 meters. The samples were prepared to identify the Ostracods and Nannofossils. The samples were taken from a depth of approximately 50 cm and have been prepared as below.For sample preparation, we placed 500 grams of a sample in a beaker and soaked it with a solution of water and hydrogen peroxide for 24 hours then the remaining sediment washed and then dried by using the sieves (30 and 60 mesh) which respectively are stacked from coarse to fine. Then all ostracods removed from each sample by brush and put on a slide. All slides were studied under a Zeiss ZH55 reflective microscope and photographed with a scanning electron microscope. Samples examined for calcareous nannofossils content were prepared using traditional smear-slide techniques. Besides ostracods from the Babafaraji section, calcareous nannofossils were also investigated, and the biozonation of ostracods has been discussed alongside the stratigraphic distribution of calcareous nannofossils. The ostracods of Abtalkh Formation in the Babafaraji section have good preservation. In this research, 31 genera and 88 species of ostracods have been identified representing a well-diversified fauna. Generally, ostracods reached their maximum diversity and abundance in the lower part of the formation and are considerably reduced towards the upper part, especially near the boundary of Abtalkh and Neyzar formations. Ostracods often are living in lakes, deep seas and oceans and are strongly influenced by environmental parameters due to sensitivity to environmental conditions more than other species. (Riha, 1995). Therefore, ostracods are useful to palaeoecology studies, reconstruction of environmental conditions, and also in determining the biological horizons and age determination of marine and continental strata on local and regional scale.

According to the stratigraphic distribution of identified species, four interval biozones are as follow:Cytherelloidea sp.1 biozone with a thickness of 210 m is equivalent to Quadrum sissinghii Zone (CC21) and the age of this zone is early Late Campanian.Alatacythere sp.2 biozone with a thickness of 273 m is equivalent to Quadrum trifidum Zone (CC22) and indicating the uppermost of Late Campanian age.Limburgina sp. biozone with a thickness of 227.5 m is equivalent to Tranolithus phacelosus Zone (CC23) and is very end of Late Campanian to Early Maastrichtian in age.Cythereis sp.12 biozone with a thickness of 73.5 m is equivalent to Reinhardtites levis zone (CC24) and indicating Early Maastrichtian age.According to the studied ostracods and corresponding with nannofossil zones, the age of Abtalkh Formation in Babafaraji section was identified upper Late Campanian to Early Maastrichtian.

The studied section is located in the eastern part of the Lut block (Iran). Lut Block represents an important structural unit of the Central and Eastern Iran. The block extends for about 900 Km in the north-south direction. It is separated from the Flysch Zone of eastern Iran by the Nehbandan fault in the east, whereas the western boundary with Central Iran is the Nayband fault and Shotori Mountains. Stocklin in 1968 believes that the Lut block could be divided into two parts (eastern and western). Camel mountain range (Shotori Mountain range) is regarded as the boundary between two parts. Based on petrological properties, it is shown that the mentioned parts are completely different from each other. In addition, various seismotectonic movements were seen in two parts that make the difference between the two parts. Dasht-e-Lut includes volcanic rocks of the Tertiary system with approximately 2000 m thickness. The volcanic rocks cover more than half of the Lut block.

Seventy-two samples for the study of the calcareous nannofossils were collected from the argillaceous limestone, pale- green marl at several different stratigraphic positions. Calcareous nannofossils were prepared in 72 smear slides using the standard techniques described by Bown and Young (1998), and studied under an Olympus Bx50 light microscope in parallel light and crossed Nicols with a magnification of 100x. Digital images of nannofossil specimens were taken with a Sony digital camera. All calcareous nannofossil specimens were identified by the taxonomic schemes of Perch-Nielsen, (1985) and Bown & Young (1998). The biostratigraphic data were interpreted by the nannofossil zonation of Sissing (1977), commonly used for the lower and upper Cretaceous in the Tethyan area.

In the studied samples, 55 species were identified. In most slides, the most common components of the nannofossil assemblages are the Watznaueria, Nannoconus, Conusphaera and Cyclagelosphaera genera. In the studied interval, the CC1 – CC5 calcareous nannofossil zones of Sissingh (1977) were recognized in the Deheshk section in eastern Iran. These biozones cover the Early Berriasian to Early Barremian in this section. The appearance of species like, N. colomii, N. dolomiticus, N. globulus, N. steinmannii minor and N. steinmannii steinmannii with Lithraphidites carniolensis, Polycostella senaria and Polycostella beckmannii at the base of this section was remarked and corresponded to the CC1 Calcareous Nannofossil Zone (Sissingh, 1977). The proposed biozones are arranged from the base to the top and they are Nannoconus steinmannii Zone (CC1), Stradneria crenulata Zone (CC2), Calcicalathina oblongata Zone (CC3), Cretarhabdus loriei Zone (CC4) and Lithraphidites bollii zone (CC5). Biostratigraphically, nannofossil assemblages suggest that the studied succession belongs to the CC1 Zone to CC5 Zone of Sissingh (1977) biozonation from the Tethyan province. According to this study and on the bases of calcareous nannofossils, the age of Baghmeshah Formation in the Deheshk section is Early Berriasian to Early Barremian.

In this study, 55 species belong to 26 genera of calcareous nannofossils were identified. Based on the present species and their comparison to the Tethyan calcareous nannofossils, the age of the Early Berriasian to Early Barremian is suggested for the studied succession that equivalent to CC1 - CC5 Zones of Sissingh (1977) biozonation.

The flysch basin of eastern Iran is in the interval between two faults, Harirud fault in the east and Nehbandan fault in the west, consisting of thick deposits of flysch- like sediments (Aghanabaty, 2004). The study area locates in the flysch Basin of eastern Iran, on the southwest of Shushud village and in the north of  Birjand (South Khorasan Province). This research carried out with the aim of identifying and introducing of ostracods and comparing the proposed biozones based on them with the provided biozones based on calcareous nannoplanktons in this region (Jalili et al., 2011). The studied section that called “Shushud section” due to its place in the southwest of Shoshud village, locates 35 kilometers far from the north of Birjand. The thick of the studied sequence is 480 m and has a lower fault boundary with a gray limestone unit. The upper boundary is covered by limestone deposits conformably.

The sampling of this section was carried out with a focus on shale and marl beds. The samples size is about 500 gr. Samples are prepared in the following way: At first, they were placed in water for 24 hours that has 10 ccs of 15 percent hydrogen peroxide for every liter of water. Subsequently, they were washed with 30 and 60 mesh sieves and then the remaining deposits were discharged into separate containers and were dried. In the next step, the ostracods in each sediment sample were transferred to a slide by a 00 size brush and were studied by a reflected microscope.

Ostracods are one of the most useful calcareous crustaceans that contain shells composed of calcareous and chitinous valves (Hadavi, 1998). Ostracods are able to live in all ecosystems and marine ostracods can live from low to high depths (about 2800 m). This microfossil group is found abundantly in marl, shale, calcareous marl, sand, silt and clay (Cohen, 2007). The Grosdidier (1973) report is one of the relatively comprehensive reports about ostracods of Iran that describes the ostracods in the Persian coastal region of Iran. The study of Shushud deposits has led to introduce 36 species belonging to 16 genera of ostracods. In this study, based on the occurrence of the identified species, three interval biozones have been recognized which are as follows: Limburgina Formosa Zone: This biozone, which covers the first 140 meters of Shushud section is defined with the first appearance of the species Limburgina Formosa to the first appearance of the species Hermanites sagittal.  Hermanites sagittal Zone: The range of this biozone is characterized by the first appearance of the species Hermanites sagittal to the first appearance of the species Schuleridea sp.1 and including the thickness of 110 m of the studied section. Schuleridea sp.1 Zone: The first appearance of the Schuleridea sp.1 species indicates the beginning of this biozone and it is the last identified biozone in the Shushud section which continues up to the end of the section and its thickness is 230 m. In the current research, the ostracods of the formation compared with the calcareous nannofossils in the Shushud section in similar horizons in terms of age (Jalili et al., 2014). After studying the nanofossils of the section, five CC20-CC26 nanofossil biozones of the Sissingh (1977) zoning were identified and the results of the study of ostracods were compared with the nannofossils. The Limburgina formosa biozone is almost equivalent to the Cratolithoides aculeus Zone (CC20) and has an age equivalent to the end of early Campanian. The Hermanites sagittal biozone is almost equivalent to the Quadrum sissinghii Zone (CC21) and is a part of the Quadrum trifidum Zone (CC22) and is equivalent to the end of late Campanian. It is worth noting that the Tranolithus phacelosus Zone (CC23) and the Reinhardtites levis Zone (CC24) are defined in the age range of the Late Maastrichtian, but due to the studied sandstone beds did not have any nannofossil, the separation of these biozones was not possible. Therefore, Hermanites sagittal biozone is about equivalent to a part of the Quadrum trifidum Zone (CC22), the Arkhangelskiella cymbiformis Zone (CC25) and Nephrolithus frequens Zone (CC26) and the age range of this biozone is the end of  Late Maastrichtian.

The introduction of 16 genera and 36 species of ostracods was identified. The identified ostracods in this section have low diversity and variety because of the unfavorable environmental conditions of the basin, as well as the effect of diagenesis in the studied section which is evident due to the hardness of most of shale and Marl deposits. Based on the detected ostracods, 3 biozones have been identified for the studied section which are as follows: Hermanites sagittal Zone, Limburgina Formosa Zone and Schuleridea sp.1 Zone.According to the introduced biozones and their correlation with the results of the study of calcareous nannofossils, the age range of the Shushud section in the north of Birjand is suggested from the end of Campanian to Late Maastrichtian.

In the present research biostratigraphy of the filyschoid deposits of the Silak section located at the eastern margin of Lut Block based on calcareous nannofossils was investigated. These deposits are about 420 m thick, and mainly contain shale, marl, calcareous sandstone and sandstone. From this section 118 samples were taken and prepared with smear slide method and then samples studied based on calcareous nannofossils. On the basis of the studied samples, 34 nannofossil species belong to 17 genera with medium preservation were identified and photographed. Based on the identified calcareous nannofossils, CC21 - CC26 biozones of Sissingh [24] in the section were determined. Determined biozones represent the late Campanian to the end of late Maastrichtian age for the investigated deposits in the Silak section. Study and comparison of the number of identified nannofossil species and determined biozones in the three sections: Silak, Sarayan and Shushud in the Lut Block show relatively same diversity of the species. However, species have better preservation in Sarayan section. In addition, difference in the biozones thickness in the studied sections may indicate a different sedimentation rate in the time interval of each biozones in different parts of the east of the Lut Block sedimentary basin.

In present study، diversity and relative abundance of calcareous nannofossils of the boundary between Abtalkh and Neyzar Formations in Dobaradar، Kalat and Chahchaheh sections were studied. Taxonomical studies of calcareous nannofossils in the studied areas led to identification of 24 species in Dobaradar، 27 species in Kalat and 32 species in Chahchaheh sections. Based on identified nannofossils and biozones، the age of the studied portions in each of sections is late Late Campanian- Early Maastrichtian. The present of Watznaueria barnesae and absence of Biscutum constans suggest low productivity and the significant increases of Micula decussata show high-stress environmental conditions in this basin.

The aim of this research was to interpret environmental conditions of the Pabdeh Formation in Ilam section، North West Zagros basin، based on calcareous nannoplankton. According to identified biozones which is equivalent to NP10-NP25 biozones of Martini (1971)، the age of Pabdeh Formation in studied section is Early Eocene – Late Oligocene. Abundance of Discoaster and Sphenolithus in the lower part of section indicates an oligotrophic condition in sedimentary basin which is related to global warming. Toward the top of section، the Cyclicargolithus floridanus، Sphenolithus moriformis، Coccolithus pelagicus، Reticulofenestrid nannofossils are dominant. On the other hand، the presences of genera Reticulofenestra، Cyclicargolithus، Dictyococcites that are taxa of temperate and cold water، indicate mesotrophic – eutrophic conditions in the upper part of section. Increasing of Discoasters shows warming trend during the Late Oligocene time.