فهرست مطالب fereshteh sajjadi

Reasonably diverse and very well-preserved palynomorphs including miospores, dinoflagellate cysts, foraminiferal test linings, acritarchs (sensu lato) and fungal spores occur in the Dalichai Formation, Yonjehzar, northeastern Tehran, central Alborz. The assemblages embrace 40 species of spores (assigned to 29 genera), 18 species of pollen (distributed among 10 genera) and 54 species of dinoflagellates (assigned to 28 genera). According to the presence of such miospores species with known worldwide stratigraphic distribution as Klukisporites variegatus, K. scaberis, Concavissimisporites verrucosus, C. pricei, Osmundacidites senectus and Striatella spp. the host strata are conceivably dated as Middle Jurassic. Based on the stratigraphic distribution of miospores, Klukisporites variegatus-Araucariacites australis-Cerebropollenites macroverrucosus Assemblage Zone is recognized. Presence of some index dinoflagellate species led to identification of four biozones in the Dalichai Formation. These include in ascending order, Cribroperidinium crispum Total Range Biozone (late Bajocian), Dichadogonyaulax sellwoodii Interval Biozone (Bathonian - early Callovian), Ctenididinium continuum Interval Biozone (early - middle Callovian) and Subzone a (early - middle Bathonian). Co-ccurrence of dinoflagellate cysts with known vertical ranges, viz., Cribroperidinium crispum, Meiourogonyaulax valensii, Carpatodinium predae, Ctenidodinium combazii and Compositosphaeridium polonicum suggests a Middle Jurassic age (late Bajocian to middle Callovian) for the host strata corroborates the available miospores-based biostratigraphy. The miospores are attributed to the Pterophyta (69%), Coniferophyta (15%), Pteridospermophyta (7%), Cycadophyta (5%), Lycophyta (2%), Ginkgophyta and Bryophytes (1%). Considering the relative abundance of fern spores (69%) and their morphological diversity (19 genera), it can be concluded that fern and fern-allies dominated the coastal vegetation around the sedimentary environments of the studied strata and that they flourished under a warm climate with notable humidity. The study of paleoclimate using the Sporomorph EcoGroups model shows a high ratio of warmer/cooler sporomorphs and a low ratio of drier/wetter sporomorphs, which is another confirmation of this type of climate. Presece of such warm water dinoflagellate cysts as Gonyaulacysta centriconnata, G. jurassica, Nannoceratopsis pellucida, Tubotuberella apatela, Ctenidodinium continuum, Pareodinia halosa, P. ceratophora, paleogeographic reconstruction and geographical location of Iran in the Middle Jurassic supports the generalization proposed.

The Baghamshah Formation (Middle Jurassic) at the Senj stratigraphic section, northeastern Tabas, central Iran, consists of diverse and relatively well-preserved palynomorphs, including spore and pollen of land plants, microscopic algae, acritarchs, Tasmanites, fungal spores, foraminiferal test linings and dinoflagellate cysts. The miospores are attributed to the Pterophyta (11%), Lycophyta (1%), Coniferophyta (80%), Cycadophyta (3%) and Pteridospermophyta (5%). Among the miospores, the maximum frequency is related to Classopollis from the Chirolpidiaceae family of conifers. The abundance of Classopollis in the studied samples may represent the abundance of Chirolpidiaceae in the composition of vegetation nearby the sedimentary environment, the abundance of produced pollen, and/or the vicinity of the habitat of the parent plants to the depositional environment. Previous investigations about the environment of the Chirolpidiaceae family indicate the predominance of hot and dry climates. The abundance of Botryococcus algae separately or attached to Classopollis also supports this type of weather. The dominant size of the miospores in the stratigraphic section (25–35 µm) indicates the transport by a wind from highland to lowland. Based on the model of Sporomorph EcoGroups (SEGs), miospores typifying all the six plant communities are present in the studied strata. The palaeoclimate study was determined by the pattern of relative abundance of drier/wetter and warmer/cooler elements. The consequences of these calculations approve the hot and dry climatic conditions during the accumulation of the strata examined.

AbstractIn order to reconstruct paleoenvironments of the Middle Jurassic Shemshak Formation, at the Namin stratigraphic section, northeastern Ardabil, western Alborz Mountains, the Sporomorph EcoGroups (SEGs) data and their associated plant communities, as well as dinoflagellate cysts, and palynological elements are employed herein. According to SporomorphEcoGroups, a high percentage of lowland plant population and a low percentage of coastal-tidal influenced and upland plant communities seem to suggest low sea-level and deposition in a shallow coastal or a marine-influenced delta. The main palynological elements occurring in the host strata are believed to reveal that the Shemshak sediments apparently accumulated in a relatively shallow, near-shore environment with low oxygen level or a marine-influenced delta. The presence in the material examined of such proximate dinoflagellates cysts as Dichadogonyaulax sellwoodii, Ctenidodinium spp., Valensiella ovulum, Pareodinia sp, Nannoceratopsis gracilis apparently supports this conclusion. Furthermore, the high ratio of warmer/cooler and low ratio of wetter/drier elements as well as the presence of warm to temperate index dinoflagellates cysts such as Ctenidodinium continuum and Pareodinia ceratophora suggests deposition of the host strata under a moist, ±warm climate during the accumulation of Shemshak sediments at the Namin stratigraphic section.Keywords: Palaeoenvironment, Shemshak Formation, Sporomorph EcoGroups (SEGs), Palynological elements, Western Alborz.  IntroductionThe Shemshak Formation was defined by Assereto (1966), based on the type area around Shemshak, north of Tehran. This Formation is a thick siliciclastic succession, widely distributed across central and northern Iran, the so−called Iran Plate (Seyed−Emami 2003, Aghanabati 2004; Seyed−Emami et al. 2008; Fürsich et al. 2009).Generally, the Shemshak Formation rests unconformably on the Lower-Middle Triassic platform carbonates sediments of Elika Formation and in turn is followed by the basinal carbonates of Dalichai Formation.The age of the Shemshak Formation ranges from Late Triassic to Early Bajocian, and sedimentary environments comprise deep to shallow marine shelf, deltas, paralic swamps, lakes and meandering as well as braided rivers (Rad 1986; Shafiei 1991; Hosainpoor 2000; Hoseinzadeh 2003; Seyed-Emami 2003; Seyed-Emami et al. 2001, 2005, 2006, 2008; Fürsich et al. 2005, 2009; Mirbaggeri, 2007; Hakimi Tehrani 2008; Reza Zadeh 2008; Taheri Serish 2018).The purpose of this study was to determine the palaeoenvironmental interpretation of the Shemshak Formation based on inferred palaeoecological preferences of dinoflagellate cysts types, and quantitative analysis of the palynological elements and Sporomorph EcoGroups in the Shemshak Formation at the Namin stratigraphic section, western Alborz. Material & MethodsA total of 46 samples (from palynologically promising intervals within the Shemshak Formation) were prepared using standard processing procedures (e.g., Traverse 2007; Phipps and Playford 1984). Samples were treated by acids (10%—50% hydrochloric acid to dissolve carbonates and 40% hydrofluoric acid to remove silicates), followed by the application of hot 50% HCl to dissolve silica-gel formed during HF treatment. The residues were then further treated with saturated ZnCl2 for mineral separation. All residues were sieved through a 20μm mesh prior to making strew slides. Three slides of each preparation were examined by a transmitted light microscope. The slides were stored in the collection of the School of Geology, Tehran University, Iran. Discussion of Results & ConclusionsDiverse and moderately preserved palynofloras dominated by miospores, dinoflagellate cysts, acritarchs, fungal spores and foraminiferal test linings occur in surface samples of the Shemshak Formation in the Namin stratigraphic section, northwestern Iran.Sporomorph EcoGroups data and associated plant communities are considered as an available approach used to draw palaeoecological inferences for their host strata (Abbink 1998; Abbink et al.2004). This method was used for the Shemshak Formation in the Namin stratigraphic section. Miospores typifying all the six plant communities are retrieved from the material examined. The least and most abundant miospores taxa are those related to Pioneer and Lowland SEGs. Based on the SEG data from the Shemshak Formation's palynological assemblages, declination of miospores representing upland/lowland plant communities as well as proliferation of those characterizing Lowland/Coastal-Tidal plant associations is interpreted to signify relatively low sea-level and sedimentation in a marginal marine setting or a marine-influenced delta.Furthermore, such palynological evidence as high frequency of proximate dinocysts and prominent equidimensional opaque/blade-shaped opaque palynomacerals ratio in the samples examined suggest accumulation in a dysoxic shallow marginal marine or a sea-influenced delta depositional setting. Additionally, the notable phytoclasts/marine palynomorphs ratio and the relative abundance of transparent in relation to opaque amorphous organic matter (AOM) seem to support this generalization.

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.

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.

In the geological history of Iran, the Mesozoic Era is of great significance since many important geological events occurred during this time interval. The tectonic and paleogeographic evolution of Iran during the Mesozoic controlled by the geodynamic interaction of Eurasian continental margin and the Tethyan oceanic belt. In the southern Alborz the Middle Jurassic marine transgression (Dalichai Formation overlying the Shemshak strata) began in upper Bajocian. The former rock unit is represented by greenish-grey calcareous shales, marls, and fossiliferous (ammonites) limestones (Steiger, 1966) widely distributed in the northern Alborz Mountains. It disconformably overlies the dark, siliciclastic coal-bearing Shemshak Formation and underlies gradually by the light-colored, rather uniform chert-bearing Lar limestones. The Dalichai Formation signifies the first rock unit of the Jurassic marine sediments in the Alborz Mountains. It embraces such diverse fauna as ammonites, belemnites, bivalves, brachiopods, echinoderms, sponges, miospores (spores and pollen grain), dinoflagellates, bryozoans and foraminifera (Stöcklin 1972; Sussli 1976; Nabavi & Seyed-Emami 1977; Alavi-Naini et al. 1982; Schairer et al. 1991; Seyed-Emami et al. 1985, 1989, 1995, 1996; Shafeizad et al. 2002; Shafeizad and Seyed- Emami 2005; Alvani 2006; , Niknahad 2007; Shahrabi 1994; Vaziri et al. 2008, 2011; Shams 2007; Makvandi 2000; Tutunchi 2001). Due to the presence of palynologically promising lithologies therein. The Dalichai Formation 8has been the subject of many palynological studies (e.g., Wheeler & Sarjeant 1990; Ghasemi-Nejad et al. 2012; Mafi et al. 2013; Dehbozorgi et al. 2013; Hashemi-Yazdi et al. 2015; Skupien et al. 2015; Dehbozorgi 2013; Saadati Jafarabadi et al. 2013; Hashemi Yazdi 2008, 2015; Orak 2010; Sajjadi et al. 2009; Sabbaghiyan 2009; Ghasemi-Nejad et al. 2008; Boroumand et al. 2011, 2013; Farisi Kermani 2003; Ghasemi- Nejad & Khaki 2002; Navidi 2013). The main aim of this study is to establish a palynostratigraphic scheme for the Middle Jurassic strata of central and eastern Alborz Mountains. A total of 104 palynological samples were collected exclusively from three outcrops of the Dalichai Formation in the central Alborz Mountains (Poldokhtar and Balu stratigraphic sections) and eastern Alborz (Lavan stratigraphic section). All samples were prepared following standard palynological processing procedures (e.g. Phipps & Playford, 1984; Traverse, 2007). Rock samples treated by acids (10%—50% hydrochloric acid to dissolve carbonates and 40% hydrofluoric acid to remove silicates); followed by application of hot 50% HCl to dissolve silica-gel formed during HF treatment. The residues then further treated with saturated ZnCl2 for mineral separation. All residues subsequently sieved through a 20μm mesh prior to make strew slides. Three slides of each preparation examined by transmitted light microscope. The slides are stored in the collection of Faculty of Geology, Tehran University, Tehran, Iran. The Middle Jurassic shales and calcareous shales are widely distributed acorss northern Iran. Diverse palynofloras comprising spores (90 species belonging to 44 genera) and 22 pollen taxa (attributed to 9 genera) occur in 104 surface rock samples collected from the Dalichai Formation at Poldokhtar, Balu, and Levan stratigraphic sections in the Alborz Ranges. In addition to terrestrial elements, such well preserved marine palynomorphs as dinoflagellates, foraminiferal test linings, tasmanites, scolecodonts, and acritarchs are also encountered in the assemblages investigated. According to the presence of such miospores species with known worldwide stratigraphic distribution as Klukisporites variegatus, Concavissimisporites verrucosus, Converrucosisporites pricei, Sellaspora asperata, Contignisporites burgeri, Osmundacidites senectus, Striatella spp. the host strata are conceivably dated as Middle Jurassic. This age determination is supported by the occurrence in the material examined of such distinct Middle Jurassic (late Bajocian-Callovian) dinoflagellates as Cribroperidinium crispum, Meiourogonyaulax valensii, Carpatodinium predae,Ctenidodinium combazii,Compositosphaeridium polonicum,and Mendicodinium groenlandicum. Based on the co-occurrence of land-derived palynomorphs a Klukisporites variegatus-Araucariacites australis-Cerebropollenites macroverrucosus Assemblage Zone is herein introduced in the Middle Jurassic strata studied.

Palaeonvironment of the Dalichai Formation، northeastern Semnan، is envisaged based on 69 samples studied palynologically. Diverse and well-preserved palynofloras، viz.، miospores، dinoflagellate cysts، foraminiferal test linings، acritarchs، wood debris (plant tissue) and Amorphous Organic Matters (AOM) occur in the material examined. The presence of relatively abundant proximate dinoflagellates and ±laevigate acritarchs in the lower part of the section studied implies sedimentation in a turbulent shallow environment. However، occurrence in the upper part of the section of abundant chorate dinoflagellates as well as notable proportion of blade-shaped to equal dimensional opaque palynomacerals seem to signify marine incursion and accumulation in an open marine setting. In most of the samples examined، prevalence of transparent AOM denotes a low oxygenated environment and slow rate of accumulation. Moreover، incidence of three palynofacies types (II، IV، VI) in the pertinent material also corroborates a shallow low oxygenated environment with low sedimentation rate which gradually deepened upward in the section.

Carbonate successions of the Sarvak Formation (Late Albian? To Mid-Turonian) together with the carbonate of the Ilam Formation formed the second important hydrocarbon reservoirs in SW Iran and Persian Gulf. Facies analyses were carried out on the upper parts of the Sarvak Formation in western part of the Ahwaz Oilfield (AZ-63 well) to interpret depositional environment. Lithologically، the upper part of Sarvak Formation is composed of clean to argillaceous limestones، which have been partly dolomitized in some intervals. Based on this study، 15 microfacies were identified that are grouped into 6 facies associations، deposited in a homoclinal ramp-like carbonate platform in the studied well. Facies distribution is also investigated in the suggested depositional model using the frequency pie-diagram. Biotratigraphic studies were carried out on microfossils of the Sarvak Formation and resulted in presentation of three biozones including Nezzazata-Alveolinid assemblage zone (Cenomanian)، Rudist debris zone (Cenomanian-Turonian) and Moncharmontia apenninica-Nezzazatinella-Dicyclina assemblage zone (Turonian). These are closely correlated with the biozonation scheme of Wynd (1965).

In order to determine the Dalichai Formation Paleoecology (Middle Jurassic)، with measured thicknesses of 255 m at Bar section، NW Neyshabour، 28 samples systematically were collected. Based on 112 Palynological slides studies، 29 species of spore and pollen، which belong to 21 genera، have been identified. In addition to spores and pollens، dinoflagellate and fungus bodies form the palynomorphs assemblages in these strata. The spore and pollen grains parental flora، in the study section، are related to Filicopsida، Lycopsida، Cycadopsida، Coniferopsida، Ginkgoopsida. Through the miospores genera of Dictyophyllidites، Klukisporites، Cyathidites، Gleicheniidites (belonging to Pterophyta) are more abundant. According to Klukisporites genera abundance، Middle Jurassic age is suggested for Dalichai Formation، at Bar section. Also، the identified dinoflagellate، type proximate which includes، Ctenidodinium ornatum، Dichadogonyaulax sellwoodii، Gonyaulacysta centriconata، Gonyaulacysta jurassica، Nannoceratopsis pellucidae، Pareodinia ceratophora، Rhynchodiniopsis cladophor، defines the warm and semi-warm climatic condition. Additionally، the presence of fungus body is also a confirmation of a warm and moist climatic condition. Finally، Dalichai Formation probably precipitated at a moist and warm climate.