جستجوی مقالات مرتبط با کلیدواژه « palaeoecology » در نشریات گروه « زمین شناسی »

In order to study the biostratigraphy and palaeoecology, the Qom Formation has been studied in the Ghamsar section of Kashan. The studied section, with a thickness of 314 m, consists of medium to thick-bedded to massive limestones and shale. The Qom Formation overlies the Eocene volcanic rocks in the Ghamsar section and is covered by the Recent alluvial sediments. A total of 21 genera and 9 species of benthic foraminifera were identified in this section and the results indicated the age of Rupelian-Chattian. According to the above palaeoecological conditions, in the lower parts of this section (Rupelian), light conditions are euphotic and nutrient conditions are first eutrophic and then Meso-oligotrophic with mainly normal sea salinity. During Chattian, the trophic state was mainly meso-oligotrophic with normal salinity, and salinity varied between 40 and 50 PSU. Light conditions also were between aphotic and mainly meso-oligophotic. Large benthic foraminifera with hyaline walls, such as Amphistegina, Lepidocyclinide and Nummulitide, in shallow environments with high energy, have thicker shells and smaller shell size, and in deep environments, due to reduced light intensity and low water circulation, they have thinner and more elongated shells. The results of the morphometry of 186 samples of Amphistegina show that the seawater depth in Ghamsar section (Rupelian-Chattian) fluctuated from less than 11 meters to less than 44 meters.

Palynological data are used for palynostratigraphy and reconstruction of some environmental parameters of the Middle Jurassic (Bajocian - Callovian) deposits at the Tapal stratigraphic section, west of Shahrood, eastern Alborz. The studied strata (Dalichai Formation) contain diverse, relatively well-preserved palynofloras, including miospores (spores and pollens), dinoflagellates cysts, fungal spores, foraminiferal test linings, acritarchs and Tasmanites. The palynofloras include 22 species of spores (belonging to 18 genera), 15 species of pollen (attributed to 9 genera) and 28 species of dinoflagellate cysts (assigned to 15 genera). Based on the stratigraphic distribution of miospores, the Klukisporites variegatus-Araucariacites australis-Cerebropollenites macroverrucosus Assemblage Zone is recognized in the sequence examined, Presence of some index dinoflagellate species led to the identification of three successive biozones including, in an ascending order, Cribroperidinium crispum Total Range Zone (late Bajocian), Dichadogonyaulax sellwoodii Interval Zone (Bathonian – early Callovian) and Ctenidodinum continuum Interval Biozone (early - middle Callovian). To reconstruct some parameters of the sedimentary environments of the studied strata, evidences such as frequency and diversity of spores attributable to ferns, relative abundance of drier/wetter and warmer/cooler elements in different plant communities, ratio of palynological elements and palynofacies, presence of index shallow water dinoflagellate cysts for instance Dichadogonyaulax sellwoodii, Ctenidodinium spp., Valensiella ovulum, Pareodinia spp., Nannoceratopsis gracilis, abundance of proximate dinocysts forms, presence of fungal spores and warm - temperate water dinoflagellate (Gonyaulacysta centriconnata, Nannoceratopsis pellucida, Gonyaulacysta jurassica, Pareodinia ceratophora) are utilized. Based on the above criteria, the material examined seems to have been deposited in a marine margin, low oxygen environment, with low rate sedimentation, under hot and humid climate conditions, where the surrounding terrestrial vegetation was dominated by ferns.

The Dalichai Formation at the Andariyeh stratigraphic section in the northeast of Andariyeh village, central Alborz Mountains, was studied by using analyses of the Sporomorph EcoGroups (SEGs) data and associated plant communities and palynofacies in order to determine its paleoecology conditions. The Sporomorph EcoGroups data from the Dalichai Formation's palynological assemblages, declination of miospores representing Upland/Lowland plant communities and proliferation of those characterizing Lowland/Coastal-Tidal plant associations interpreted to signify relatively low sea level and deposition in a marginal marine setting. Furthermore, the ratios of wetter/drier and warmer/cooler elements suggest deposition of the host strata under a moist, ±warm climate prevailing during the Middle Jurassic in central Alborz Mountains. The results of drawing diagrams of the palynofacies in the Andariyeh stratigraphic section, indicates that the Dalichai sediments accumulated in a dysoxic shallow marine environment with low sedimentation rate that corresponds well with its SEGs graphs.

Abstract Well preserved and diverse organic-walled marine microphytoplankton cysts (acritarchs sensu lato) occur in Member 4 (comprising mostly of fine-grained clastics with thin carbonate intercalations) of the Mila Formation at the type section, southwestern Damghan. Based on the association of such index acritarch taxa as Timofeevia phosphoritica, Cristallinium cambriense, Ninadiacrodium dumontii, Vulcanisphaera africana, Ooidium rossicum, Cymatiogalea cuvillieri, Caldariola glabra, and Dasydiacrodium sp. in the material studied, an local biozone, namely Ooidium rossicum -Vulcanisphaera africana assemblage biozone dated as Late Cambrian (Furongian), and a barren interval are introduced in the upper and lower parts, respectively, of the rock unit investigated. Occurrence in the examined assemblages of such middle latitude acritarchs as Ninadiacrodium indicates that the Alborz Ranges was located in southern mid-latitudes (30º–60º) during the Late Cambrian. Retrieved marine microphytoplankton cysts from Member 4 of the Mila Formation is comparable with the Late Cambrian assemblages recorded from elsewhere, this allows for the pertinent assemblages to be associated with peri-Gondwanan palynofloras. Keywords: Biostratigraphy, Palaeoecology, Acritarchs, Late Cambrian, Mila Formation.   Introduction Biostratigraphic zonation of the Middle and Upper Cambrian strata is based mainly on trilobites, particularly planktonic agnostids and olenids. For example, in South China base of the Furongian Series is defined by Glyptagnostus reticulatus Zone (Peng et al. 2004). In the last decades, organic-walled microfossils (acritarchs) have been widely used for Palaeozoic stratigraphic subdivisions (Molyneux et al. 1996). The Acritarch group is defined as organic-walled microfossils of unknown biological affinities by Evitt (1963). They are a heterogeneous group of various microfossils and may include the remains of a wide range of different kinds of organisms, such as egg of small metazoans, spores of different algal classes, and resting cysts (Servais 1996). Recently, some of the acritarchs have been attributed to different groups of algae e.g. Prasinophytes or Chlorophytes (Colbath and Grenfell 1995). In the last decades, organic-walled microphytoplankton have been widely used for stratigraphic correlation both regionally and globally and their utility in dating Proterozoic and Palaeozoic marine sedimentary rocks is widely recognized (Playford 2003). Acritarchs feature a relatively rapid development of morphological innovations and a large number of new morphotypes appeared. Several palynological investigations have been undertaken on the Upper Cambrian strata across the world; e.g., Canada (Martin and Dean 1988; Palacios 2012), Russia (Raevskaya and Golubkova 2006), Germany (Montenari and Servais 2000), Iran (Ghavidel-Syooki 2006; Ghavidel-Syooki and Vecoli, 2008), North Africa (Vecoli 1999), England (Potter et al. 2012) and Spain (Albani et al. 2006). The Mila Formation is the first lithostratigraphic unit representing the Middle–Upper Cambrian strata in the Alborz Ranges and the other parts of Iran (Aghanabati 2004). Palaeontological and structural geological studies in the Alborz indicate that northern Iran, along with central Iran and Zagros located on the divergent margin of protopaleotethys and north of the Gondwana palaeocontinents. The Mila Formation at its type section measured 585 m (Stöcklin et al. 1964) and subdivided into five members: Member 1, dolostone–marl; Member 2, terrigenous – carbonate; Member 3 fossiliferous limestone; and mainly terrigenous members 4 and 5. According to palaeontological and stratigraphical studies the first 2 units attributed to the Middle Cambrian and members 3 and 4 to the Late Cambrian. The former Member 5 of this unit was later considered to be equivalent of the Lashkarak Formation (Early Ordovician). The Mila Formation at the its type section is underlain and overlain by the Lalun and Jeirud formations, respectively. The Mila Formation generally consists of dolostone, thin-bedded, crystalline, glauconitic limestone, marl, coloured shales and sandstones. Several palaeontological investigations have been conducted such as on trilobites (Kushan 1973; Peng et al. 1999), brachiopods (Popov et al. 2009, 2013), conodonts (Müller 1973; Fazli and Hamdi 2008; Jahangir et al. 2016) and palynomorphs (Ghavidel-Syooki 2006). Considering the stratigraphic significance of organic-walled marine microphytoplankton in the Lower Palaeozoic biostratigraphy, the aim of this study is to determine relative age and to derive palaeogeographic implications for the Member 4 at its type section.   Material & To retrieve palynological content of the Member 4 of Mila Formation at the type section, 21 surface samples collected from this rock unit. All samples prepared in palynological laboratories at Kharazmi University, Tehran and University of Lille, France using standard palynological processing procedures, encompassing initial treatment with HCl 10-50% and HF 40% for dissolution of carbonates and silicates, respectively. Then the residues saturated with ZnCl2 solution (2.0 gr/cm3) for mineral separation. All residues are sieved with 15 and 20 µm mesh and three slides of each sample are made.   Discussion of Results & Well-preserved and diverse palynomorphs occur in Member 4 of the Mila Formation at the Mila Kuh section. The assemblage contains 14 species assigned to 13 genera of acritarchs and one species of prasinophytes. Based on the occurrence and stratigraphic distribution of index acritarch taxa such as Timofeevia phosphoritica, Cristallinium cambriense, Ninadiacrodium dumontii, Vulcanisphaera africana, Ooidium rossicum, Cymatiogalea cuvillieri, Caldariola glabra, and Dasydiacrodium sp. one local assemblage biozone namely Ooidium rossicum-Vulcanisphaera africana assemblage biozone is introduced in 41 m of the Member 4 and assigned to the Late Cambrian (Furongian). Additionally, one barren interval zone at the base (45 m) of the rock unit is also identifiable. The biozone (Ooidium rossicum-Vulcanisphaera africana) introduced herein is comparable to microflora A2 (partial) – A6 of Martin and Dean (1981, 1988) and RA3–RA10 microflora of Parsons and Anderson (2000) as well as the upper part of VK2 to VK5 of Volkova (1990) at the East European Platform. Furthermore, it is equivalent with the Zone II to IV of Ghavidel-Syooki and Vecoli (2008) in the High Zagros Mountains, southern Iran. Occurrence of such mid-latitude taxa as Ninadiacrodium and comparison of the acritarch assemblages with those from elsewhere in the world indicates the peri-Gondawanan affinity; thus supporting a 30°-60°S palaeolatitude for the eastern Alborz in the Late Cambrian

Diverse, moderately to well-preserved palynomorphs including acritarchs (sensu stricto), prasinophytes cyst, chitinozoans, scolecodonts, and spores occur in some surface samples (90 meters thereof) of the Niur Formation (200 m thick) at the Tikdar stratigraphic section, northern Kerman, Central Iran. The palynofloras embrace one species of prasinophyte cyst, 25 species (assigned to 14 genera) of acritarchs, 8 species (attributed to 6 genera) of chitinozoans, and 2 species (assigned to 2 genera) of spores. Based on the stratigraphic distribution pattern of acritarchs (sensu lato) one local assemblage zone (Evittia denticulata denticulata - Lophosphaeridium papillatum-Eupoikilofusa striatifera assemblage zone) is introduced in the strata investigated herein. The known stratigraphic importance of such acritarchs and chitinozoans as Eupoikilofusa striatifera, Geron amabilis, Spinachitina fragilis and Ancyrochitina convexa as well as the lack of Middle and Late Silurian index taxa allow for the host strata to be attributed to the Early Silurian (Llandovery). Notable abundance of transparent AOM in majority of the samples (except those labeled as 318–326 and collected 38–88 above the base) examined indicates sedimentation in a marginal marine setting with relatively low oxygen level. Such palynofacies data as proportion of blade-shaped to equidimensional opaque palynomacerals and AOM/marine palynomorphs ratio in the material studied tend to support such generalizations on the depositional environment.

Economically the Surgah Formation is the most significant in the Zagros sedimentary basin. In this study, the calcareous nannofossils have been investigated of the Surgah Formation from the Shah-nakhjir section. The thickness of the Surgah Formation is about 147 meters and composed of marly limestone deposits with diversity and well-preservation of calcareous nannofossil assemblages. In total, 41species belong to 22 genera were determinate and ultimately have compared with nannofossil standard zones. According to identified nannofossils, the age of the Middle Cenomanian- Middle Santonian corresponding to CC10- CC17 (Sissingh, 1977) includes Microrhabdulus decoratusZone (CC10), Quadrum gartneri Zone (CC11), Lucianorhabdus maleformis Zone (CC12), Marthasterites furcatus Zone (CC13), Micula decussataZone (CC14), Reinhardtites anthophorus Zone (CC15), Lucianorhabdus cayeuxii Zone (CC16), Calculites obscurus Zone (CC17) were suggested for the Surgah Formation in the studied section. Palaeoecological interpretations based on the identified species show warm climate and low depth conditions in low latitudes for deposits of the Surgah Formation in southwest of Ilam city (Shah-nakhjir section).

The aim of this study is determining systematics and identification of ostracods genera and species of the e Member of the Qom Formation at the studied section (Cheshmeh Boroun) for biostratigraphy and age determination, and palaeoecological investigations considering the abundance and diversity changes of ostracods based on the collected data.
The abundance and diversity of the ostracods taxa such as Paracypris¡ Aurila ¡Ruggieria ¡Loxochoncha ¡ Krithe¡ Xestoleberis, Cytherella mostly suggest a marine environment with normal salinity and warm climate from ecological point of view. However, the increase and decrease of these taxa in the studied section indicate the diversity and abundance changes is related to environmental changes. In fact, this shows the instability of the environmental conditions which seems to be affected by the changes of food and oxygen values, and water turbulence. Based on ostracods assemblages, an Early Miocene age ( Aquitanian- Burdigalian) is exclusively suggested for the e Member of the Qom Formation at Cheshmeh Boroun stratigraphic section.

Sporomorph EcoGroups data and the relevant plant communities are considered as a possible routine used to draw palaeoecological inferences for their host strata. Occurrence of high abundant, diversity and well preserved miospores in the Dalichai Formation of the central and eastern Alborz Ranges allows for this method to be used to obtain certain palaeoecological implications of its depositional environment. The misopores are classified as Sporomorph EcoGroups (SEGs) that with reference to their parent plants each indicate particular palaeocological specifications.
According to the SEG data derived from study of the Dalichai Formation's palynological assemblages, declination of miospores representing Upland/Lowland plant communities and the proliferation of those characterizing Lowland/Coastal-Tidal plant associations is interpreted to signify relatively low sea level and sedimentaion in a marginal marine setting.
Furthermore, the ratio of wetter/drier and warmer/cooler elements suggests deposition under a moist, ±warm climate during the Middle Jurassic in central and eastern Alborz Mountains. Notable abundance of the fern spores in the palynofloras studied tends to support this palaeoclimate generalization.

The triangular-shaped central Iran Microcontinent, being located almost in the middle of Iran, is bounded on the north and south by the Alborz Ranges and Makran Zone, respectively. During Silurian and Devonian, parts of the Iran Plate including Alborz, central Iran, and Sanandaj-Sirjan as well as Afghanistan and Turkey joined Saudi Arabia and Africa, forming the southern shorelines of Palaeotethys along the northwestern margin of Gondwana. The Late Ordovician-Late Devonian palaeogeographic maps of northern Saudi Arabia allude to the existence of a vast stable shelf along the northern margin of the Gondwana, i.e., northern Africa and Saudi Arabia (Berberian and King 1981; Husseini 1991; Sharland et al. 2001; Ruban et al. 2007; Al-Juboury and Al-Hadidy 2009; Torsvik and Cocks 2009).
The Upper Palaeozoic strata of northern Kerman comprise diverse marginal marine sediments embracing, inter alia, the Shishtu Formation. Well-preserved, diverse palynofloras including marine microphytoplanktons (acritarchs and prasinophytes), spores, scolecodonts, and chitinozoans are retrieved from the latter and its correlatives in the Zagros Mountains and central Alborz Ranges (Hashemi & Playford 1998; Ghavidel-Syooki 198; Hashemi & Fahimi 2006; Hashemi & Tabea 2006).
Material and This study is based on palynological analysis of 20 surface rock samples collected from palynologically promising levels of the Shishtu Formation, Kuh-e-Tir as cropped out in northwest of Kerman; i.e., grey-black shales and fine-grained sandstones therein. To prevent/reduce the risk of contamination and/or palynomorphs oxidation, samples collected from ca. 20-50 cm below the surface (Wood et al. 1996). Conventional laboratory methods (e.g., Barss and Williams 1973; Phipps and Playford 1984; Wood et al. 1996) used to retrieve and to concentrate palynomorphs from the host strata. Three strew-slides made from each residue used for the light microscopy that was undertaken at the Department of Geology, Faculty of Earth Sciences, Kharazmi University, Tehran, employing a Zeiss Axioplan 2 microscope equipped with a digital Canon Power Shot G5 camera.
Discussion of Results and Relatively diverse, poor-moderately preserved palynofloras comprising of marine microphytoplanktons acritarchs (8 species distributed among 3 genera), prasinophytes (3 species assigned to 2 genera), spores (52 species attributed to 21 genera), scolecodonts, and chitinozoans occur in surface samples of the Shishtu Formation, Kuh-e-Tir, northwestern Kerman. Of the microphytoplanktons, Lophosphaeridium and Leiosphaeridia are relatively more abundant. The spores are mostly radiosymmetrical and trilete; bilateral, monolete forms such as Laevigatosporites rarely occur. Acavate taxa, namely, Leiotriletes, Punctatisporites, Apiculatasporites, and Planisporites, such cavate forms as Vallatisporites and Grandispora, and the distinctive cingulate taxon, Densosporites, dominate the land-derived palynofloras.
Stratigraphic distribution pattern of the spores allows for the introduction of two informal successive assemblage biozones, viz., assemblage biozones a and b in the Shishtu Formation at the section investigated. The former can be identified with the co-occurrence of such distinct species as Cristatisporites triangulatus, Geminospora lemurata , Punctatisporites stabilis Grandispora inculta, Apiculatasporites sp. cf. A. perpusilus, Grandispora sp. cf. G. eximia, Grandispora sp. cf. G. artusa. It contains such key species of the north American early Late Devonian (Frasnian) as optivus-triangulatus, lemurata-magnificus, ovalis- bulliferus Assemblage Zone (Richardson and McGregor 1986). Characterized by the association of Retispora lepidophyta, Geminospora punctata, Densosporites spitsbergensis, Leiotriletes ornatus, Amicosporites jonkeri, Apiculatasporites adavalensis, Densosporites cassiformis, the assemblage biozone b comprises characteristic taxa of the late Late Devonian (Famennian) pussilites-lepidophyta Assemblage Zone of the previously mentioned biozonation scheme. The absence in the material examined of such distinct marine microphytoplanktons as Unellium lunatum, Unellium piriform, Cymatiosphaera perimembrana, Daillydium pentaster, Chomotriletes vedugensis is noteworthy as they have already been recorded from ±co-eval strata from elsewhere in Iran. A brachiopod referred to as Strophomenid, is the sole palaeontological evidence yet reported from the host strata based on which the rock unit dated as late Famennian-early Tournaisian (Wendt et al., 2002).
In the material investigated terrestrial palynomorphs (spores) dominate the marine microphytoplanktons in terms of both abundance and diversity. The acritarchs and prasinophytes encountered are generally with ±circular vesicle, relatively thin eilyma bearing fairly short sculptural elements or being virtually psilate; such complexion indicates accumulation of the host strata in a shallow marginal marine setting. Spore-parent plant relationships testify to the presence of a contemporaneous coastal vegetation dominated by Progymnospermopsida, Lycopsida, Filicopsida, Equisetopsida; apparently these were accompanied by less abundant representatives of Barinophytopsida, Zoesterophyllopsida, Rhyniopsida, Ginkgopsida, Cycadopsida.

The Nayband Formation in North of Isfahan includesfive Members: 1- Gelkan Member (marl and sandstone), 2- Bidestan Member (sandstone and reefal limestone), 3- Howz- e- Sheikh Member (marl and sandstone), 4- Howz- e- Khan Member (marl and reefal Limestone) and 5- Qadir Member (marl and sandstone). The biostromal limestones of Bidestan and Howz-e- Khan Members represent a typical known key bed in North of Isfahan. In Bidestan and Howz-e- Khan Members (NaybandFormation), coral reefs grow up and their distribution are significant in the biostromal limestone of Bidestan and Howz-e- Khan Members of Nayband Formation.Twelve genera and 31 species of Scleractiniancorals were recognized in thesereefal members. They included: Reimaniphylliidae, Margarophylliidae,Coryphylliidae,Cyclophyllidae, Astraeomorphidae,Pamiroseriidae, Stylophyllidae andActinastraeidae families. According to the field observations and evidences, laboratory studies and analysis, measurements of the coral size and the destroyedepitechaof thecorals, it could beguessed that Scleractinian corals survive below the storm wave base (about 20 meters depth) but they tolerated many storms. Morphology of Scleractinian corals of Late Triassic sea (North of Isfahan) indicatesinadequate living conditions and high energy environment. Corals have major roleinreconstruction of Paleoenviromentofthe LateTriassic unitsofthe North of Isfahan (Nayband Formation) in Dizlusection.

Palynological data are used to draw palaeoecological inferences for the Dalichai Formation (Bajocian - Callovian) in two stratigraphic sections, Balu in central Alborz and Tapal in eastern Alborz. Diverse and reasonably well preserved palynofloras consisting of miospores, dinoflagellate cysts, acritarch cyst and foraminiferal test linings are present in the host strata. Miospores (spores and pollen) were used to interpret the palaeoecological and palaeoclimatical conditions of the Dalichai Formation at these stratigraphic sections studied. Affinities of the Dalichai Formation’s miospores at the Balu section in central Alborz appear to be with the Pterophyta 49%, Coniferophyta 23%, Ginkgophyta 15%, Lycophyta 8%, Sphenophyta 4%, and Bryophytes 1%. Similarly to the Balu section, Pterophyta exhibits remarkable percentage (49%) at the Tapal section in eastern Alborz, followed by Coniferophyta 26%, Ginkgophyta 19%, Lycophyta 4%, Bryophytes 2% and Sphenophyta 1%. Compared with the distribution of modern plants, spore-pollen assemblages of these two stratigraphic sections reflect a wet warm climate during the Middle Jurassic Dalichai Formation in central and eastern Alborz.

The thick layers of late Aptian- early Cenomanian deposits in the northwest of Kerman, which consist of mainly marl and limestone has been sampled and studied. The thickness of the succession in the Basab area is 380 meters and is subdivided into 4 distinct and informal units that named Lower Basab Marl, Lower Basab Limestone, Upper Basab Marl and Upper Basab Limestone. The base of this section overlies paraconformably the Jurassic (Liassic) sandstones, while the upper boundary is an erosional surface and covered by the Neogene deposits. Among the macrofossil assemblages that found in this section, the Oysters that belong to three families of Gryphaeidae, Palaeolophidae and Ostreidae are more abundant. The Gryphaeidae family with 80% is more abundant than other families and discussed in this paper. Seven genera and species of this family are reported. Palaeoecological studies and taphonomy effects on the surface of specimens show a warm, shallow environment (intertidal and sublittoral) with a high energy during the deposition of the strata. The Oysters in studied area is very similar to those specimens reported from Egypt in the Wadi Qena Basin.

For study of systematic and palaeoecology of Mid-Cretaceous Oysters, the Basab section, with 380 m thickness, west of Kuhbanan, northwest of Kerman, was measured and sampled. The section comprises a high diverse fauna (macro and microfossils), such as Echinoids, Bivalves, Oysters, Brachiopods, Gastropods, Corals, Ammonites, Foraminifers and Ostracods. The fossils indicate Late Aptian- Early Cenomanian age for the studied section. Eleven genera and species of Mid-Cretaceous Oysters are reported for the first time from the region. The fossils assemblages show a shallow and favorable condition during the deposition of the strata. The study of the Oysters indicates that the peak of abundance of the fossils correlates with high values of δ13C curve. This implies deposition of high amount of organic carbon, low oxygen condition, elimination of other taxa and opportunistic character of the Oysters.

In This study، large benthic foraminifera of Qom Formation in Chenar area (northwestern Kashan) with 147 m thickness are investigated. 112 thin sections were prepared and distribution of benthic foraminifera was analyzed to reconstruct paleoenvironmental condition. Sea level fluctuations could be observed from bottom to top in the studied section. Based on large benthic foraminifera assemblages and microfacies features، three major depositional environments (inner shelf، middle shelf & outer shelf) were defined. The inner shelf facies is characterized by wackstone-packstone، dominated by miliolid and small perforate foraminifera. The middle shelf facies is represented by packstone-grainstone with diverse assemblage of large perforate benthic foraminifera. Outer shelf facies is dominated by large perforate benthic foraminifera as well as planktonic foraminifera. The distribution of the Oligocene large benthic foraminifera in the studied area indicates that shallow marine carbonate sediments of the Qom Formation were deposited in a photic zone of tropical to sub-tropical environments.

In this research, biostratigraphy and palaeoecology of the Sarvak Formation (208 meter thickness) in southwestern Firozabad, has been studied. Paleontological and biostratigraphical studies resulted in the identication of ve faunal assemblages. The biostratigraphic study led to recognition of ve biozones, in ascending order biozones are as follow: Conicorbitolina conica - Trocholina assemblage zone, Favusella washitensis range zone,Rudist debris zone, Nezazzata – Alveolinides assemblage zone, and Oligosteginids assemblage zone. According to these biozones, the Sarvak Formation is Late Albian-Cenomanian in age. Palaeoecological analysis yielded four assemblages. The rst assemblage is composed of big conical and agglutinated foraminifera with low diversity. The second assemblage is mostly composed of large conical and agglutinated foraminifera and also small agglutinated foraminifera. This assemblage has diverse fossils. The third assemblage includes small agglutinated foraminifera and no large conical and agglutinated foraminifera are observed, the diversity in this assemblage is variable. The fourth assemblage is different from other three assemblages and includes oligosteginidae and planktonic foraminifers. The diversity in this assemblage is also variable. Differences between fossil assemblages are mainly interpreted and related to ecologic and biotic conditional changes such as: oxygen contents, depth, disappearance of symbiosis algae, sedimentation rate and type of bottom sediments (substrates).