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

The spores and pollen (miospores) are classified as Sporomorph EcoGroups (SEGs). Relative frequency changes within successive sporomorph assemblages predominantly reflect changes in parent plants communities composition, on the other hand changes in the plant macrofossil communities composition also reflect paleoclimatical and paleoenvironmental changes. Occurrence of well-preserved miospores in the Dalichai Formation at the Kanz stratigraphic section (central Alborz) and Talu stratigraphic section (eastern Alborz) allows for this method to be used to recognition of certain paleoecological and paleoenvironmental inferences of this formation. Quantitative analysis of the sporomorphs shows various plant communities, which coexisted during the deposition of the Dalichai Formation at the both stratigraphic sections: Upland, Lowland, River, Pioneer, Coastal and Tidally-influenced. Changes in Upland/Lowland and Lowland/Coastal+Tidally influenced ratios accompanied by quantitative palynofacies analysis at the Kanz and Talu stratigraphic sections indicate low sea level at the beginning of the formation, which gradually towards the end of the both stratigraphic sections, the sea level is rising and the basin is witnessing a slight increase in depth. The depth of the basin has increased more compared to the previous stage and continues until the deposition of nodular limestones of the Upper Jurassic Lar Formation. The Relative frequency pattern of warmer/cooler and wetter/drier elements represents a moist, ±warm condition during the deposition of the Dalichai Formation at the both stratigraphic sections. This general paleoclimate reconstruction is also supported by abundance of fern spores in the study material.

Abstract The Dalichai Formation in the Ahvanu section, north of Damghan city, with a thickness of 78 meters, comprises alternations of bluish-gray marls and limestones. Microfacies and palynofacies studies, along with fossil evidence, including foraminifera diversity and abundance, the ratio of epifaunal to infaunal benthic foraminifera, and the ratio of surface to deep infaunal, were utilized to identify organic-rich layers and reconstruct trophic levels. These factors confirm a mesotrophic environment with average oxygen and nutrient levels for the Dalichai Formation (Bajocian to Lower Callovian) in the studied section. The primary reasons for low organic matter in the Dalichai Formation are attributed to low production and poor preservation of organic matter. However, dark-colored deposits with high organic matter at the Bajocian–Bathonian boundary and the lower and upper Callovian boundaries suggest increased production rates in anaerobic and eutrophic conditions. Macrofossil fragments (ammonites and echinoids) within limestone deposits at the uppermost part of the Dalichai Formation, exhibiting low organic matter, and the presence of Zeophycus trace fossils, suggest an oligotrophic environment with dysoxic conditions in the Upper Callovian.

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.

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.

Stratigraphic and sedimentology studies have been carried out on sixty-nine rock samples related to the one hundred fifteen meters thickness of the Dalichai and Lar formations in the southeast of Zanjan. The carbonate layers of the Dalichai Formation with seventy-eight meters thickness overlay the strata of the Shemshak Group/Formation (the boundary has been covered) and are overlaid by thirty-seven meters thickness of carbonate layers of the Lar Formation with gradual boundary in this area. There are some sedimentological changes in the succession across the Dalichai-Lar formations boundary such as color changes, bedding thickness changes from medium to thick, disappearance of Thalassinoides facies, chert nodules, and Ammonite/Belemnite facies and finally changes in microfacies from mudstone to the wackestone/packstone (deeper to the shallower). The Lar Formation is the youngest formation in this area that has been covered by the Quaternary sediments. Five lithofacies have been identified based on field and microscopic studies: 1- Pelloidal packstone with intraclasts, 2- Pellet/oncoid wackestone/packstone, 3- Mudstone with Thalassinoides, 4- Bositra buchi pelagic packstone and 5- Pelagic mudstone that shows basin and outer ramp as depositional environments for the Dalichai and Lar formations in this section. Field and facies studies show a deepening upward trend to the middle parts of the section (upper parts of the Dalichai Formation) and followed by shallowing upward trend to the upper parts (Lar Formation) of the section.

The Dalichai Formation in Ahvanu section in the north of Damghan city with a thickness of 78 meters consisting of an alternation of bluish-gray marls and limestone, was studied. Based on the presence and stratigraphic distribution of miospore, Klukisporites variegatus and Callialasporites dampieri of pollen are identified (Middle Jurassic) and presence of some index dinoflagellate species led to the identification of three 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 to middle Callovian). Also, this Formation was divided into two biozone on the basis of Lenticulina   varians-Ophtalmidium Assemblage zone and Globigerina bathoniana Taxon range zone. The close similarities of fauna assemblages of Dalichai Formation in this region (eastern Alborz ((dinoflagellate cyst, foraminifera, posidonia and radiolar) with assemblages recorded from different parts of Iran (such as central and eastern, western Alborz and Binalud and south of Iran) and other parts of world (northwest of Europe, and the northwestern Tethys and …) confirm the marine connection and faunal exchange between the mentioned basins during Middle Jurassic.

The Middle Jurassic strata (Dalichai Formation) is widespread across the Alborz Range. It is chiefly characterized by alternating shale beds, bluish-grey thin to medium bedded limestone, and marl including ammonites, belemnites, and sponge (Steiger, 1966). Various mega- and microfossil faunas are recorded in the formation, including fairly rich ammonites, spores, pollen grains, dinoflagellate cysts, belemnites, bivalves, brachiopods, echinoderms, sponges, bryozoans, and foraminifera. The 212-m-thick Dalichai Formation in the Bashm stratigraphic section, Eastern Alborz, mainly consists of marl, argillaceous limestone, and a few intercalations of cherty limestone. With distinct disconformity, it succeeds the Upper Triassic-Lower Middle Jurassic Shemshak Formation and gradationally underlies the thick-bedded limestone of the Upper Jurassic Lar Formation. This study aimed to make and correlate a palynostratigraphic framework for the studied interval and interpret the palynofacies and paleoclimate of the Dalichai Formation based on palynological data at the Bashm stratigraphic section, Eastern Alborz, northern Iran.

In the studied section, twenty-four samples were collected for palynological analysis. All samples were prepared following standard palynological processing procedures (e.g., Phipps & Playford, 1984), comprising treatment with hydrochloric (10-50%) and hydrofluoric (ca. 40%) acids for dissolution of carbonates and silicates, respectively. Thereafter, hot 50% HCl was used to dissolve silica-gel formed during the HF-silicate reaction. Then the solution was neutralized and centrifuged in ZnCl2 (specific gravity 1.9) for density separation. Neither oxidative nor alkali treatments were applied. Residues were sieved through a 20μm mesh and strew mounted on glass slides using liquid Canada balsam. All the samples, slides, and figured specimens were stored at the Laboratory of Paleontology of the Department of Geology, Faculty of Science, Imam Khomeini International University, Qazvin, Iran.

The 24 samples examined yield well-preserved, diverse palynofloras consisting predominantly of dinoflagellate cysts and miospores (spores and pollen grains). Fungal spores and acritarchs occur as minor constituents. The presence of some index species of dinoflagellate cysts leads to the identification of three of the North-western European biozones (Woollam & Riding, 1983; Riding & Thomas, 1992; Poulsen & Riding, 2003), i.e., Cribroperidinium crispum Total Range Biozone (late Bajocian), Dichadogonyaulax sellwoodii Interval Biozone (Bathonian to early Callovian) and Ctenidodinium continuum Interval Biozone (early to middle Callovian). Moreover, the presence of such dinoflagellate species as Mendicodinium groenlandicum and Systematophora areolata has been used to attribute a late Callovian age to the upper part of this studied section. Therefore, the late Bajocian - late Callovian age is collectively attributed to the studied section. This age assignment based on palynological data is consistent with the age presented by the ammonites (Hossein Zadeh, 2011) in this stratigraphic section. The erected palynozones correspond largely to those established in Northwestern Europe and reveal the marine connection between North of Iran with Northwest Europe and the Northwestern Tethys during the late Bajocian to late Callovian ages. Quantitative analyses of the palynological data indicate the dominance of a relatively shallow, low-oxygenated marine environment with a relative increase in depth at some intervals upward in the studied section. Such spore species as Klukisporites, Cyathidites, Dictyophyllidites, and Gleicheniidites known to have been produced by Pterophyta dominate the palynofloras. Thus, the contemporaneous coastal vegetation was characterized by the predominance of Pterophyta and minor components of Ginkgophyta, Pteridospermophyta, Coniferophyta, Lycophyta, and Cycadophyta. Moreover, this reconstruction accompanied by the dominance of warm and intermediate dinoflagellate cysts collectively indicates a mild to warm climate for the Dalichai Formation in the studied section during the Middle Jurassic (late Bajocian - late Callovian). Indeed, according to the paleogeographic maps, in the Middle Jurassic (Middle Callovian), the Alborz Mountains of northern Iran occupied lower latitudes between 20 to 30 degrees north (Thierry, 2000; Seyed-Emami et al., 2008; Wilmsen et al., 2009, 2010). This position confirms this paleoecology for the Dalichai Formation.

All samples examined yield well-preserved, diverse dinoflagellate cyst assemblages. 26 identified dinoflagellate cyst species led to the identification of three biozones: Cribroperidinium crispum (late Bajocian), the Dichadogonyaulax sellwoodii (Bathonian to early Callovian), and Ctenidodinium continuum (early to late Callovian). Due to such dinoflagellate species as Mendicodinium groenlandicum and Systematophora areolata, a late Callovian age is attributed to the upper part of the studied section. This age assignment is consistent with the age presented by the ammonites in this stratigraphic section. Palynological data designate the dominance of a relatively shallow marine environment with a relative increase in depth at some intervals upward the studied section. The abundance of intermediate and warm water dinoflagellate cysts and ferns in the surrounding area of the Dalichai Formation depositional setting and also fungal spores collectively indicate a mild to warm climate for the Dalichai Formation in the studies section.

The Dalichai Formation in Parikhan section in the west of Shahrood with a thickness of 250 meters consisting of an alternation of bluish-gray was studied. This formation overlies the Shemshak formation disconformity, and it has gradually been covered by the thick-bedded limestones of the Lar formation. The biogenic components consist of brachiopods, gastropods, bivalves, ammonites, echinoderms, belemnites, sponges and sponge spicules, radiolarians, ostracods, benthic foraminifers. The aim of the present study is to discuss the age of the formations and paleobiogeography relationship based on foraminifera and dinoflagellate cyst assemblage.

The Parikhan section is located on the central part of Alborz Mountains, approximately 14 km west of Shahrood (coordinates with E 54° 49΄11 ˝ and N 36° 24΄20˝). 27 samples were collected systematically and processed for palynostratigraphy following the standard palynological technique described in Traverse (2007). Cold hydrochloric (30 %) and hydrofluoric acids (30 %) were used to dissolve carbonate sand silicates, respectively. The residue was neutralized and centrifuged in ZnCl2 with specific gravity (1.9 g/cm3). The materials were then sieved using a 15-μm nylon mesh and mounted on microscope slides using liquid Canada balsam. The present study shows that the Dalichai Formation is rich in terrestrial (spores and pollen grains) and marine palynomorphs (dinoflagellate cysts, acritarchs, and scolecodonts). In the laboratory, thin sections were prepared from all marly limestones and hard resistant shaly marl samples to achieve further microfossils evidence and aid sedimentological descriptions. All samples were processed for foraminiferal analysis following the standard method of Lirer (2000). Thus, 21 species belonging to 17 genera of planktonic and benthonic foraminifera were identified.

In the present study, 30 species of dinoflagellate cysts belong to 22 genera and 10 species of spore, which belong to 8 genera, and 7 species of pollen, which belong to 4 genera, have been identified. Based on the presence and stratigraphic distribution of the most dominant miospore, Klukisporites variegatus and Callialasporites dampieri of pollen are identified in the Dalichai Formation (late Bajocian - Callovian). Based on recorded dinocyst assemblages, especially marker species, three palynozone, including Cribroperidinium crispum Total Range Zone (late Bajocian), Dichadogonyaulax sellwoodii Interval Zone (Bathonian – early Callovian), and Ctenidodinium continuum Interval Zone (late Callovian) were identified.

The Middle and Upper Jurassic sedimentary well successions is located in the northwestern Damghan, (eastern Alborz range). The Dalichai Formation with a thickness of 618 meters in the studied section consists of marl, limestone and marly limestone. The lower boundary with the siliciclastic of the underlying Shemshak Formation is unconformable and in the upper boundary is gradually covered by the Lar Formation. From studied section, altogether 371 fossile sample were collected of which 15 sample were related to other taxon (Bellemnite, Bivalve, Coral and Sponge). Altogether, 51 species of ammonites from the Dalichai Formations belonging to 25 genera and 9 families and 14 zones are described. The following families are reported: Phylloceratidae, Lytoceratidae, Haploceratidae, Oppeliidae, Parkinsoniidae, Morphoceratidae, Reineckeiidae, Perisphinctidae and Aspidoceratidae. Based on ammonites, the Dalichai Formation ranges from the Upper Bajocian to Lower Kimmeridgin and can be subdivided, from bottom to top, into six informal members. Palaeobiogeographically the ammonite fauna is closely related to that of the sub-Mediterranean Province of the northwestern Tethys.

The Binalud Mountains in the northeast of Iran is a limited structural unit between the central Iran, Kopet-Dagh, and Alborz Mountains, mainly considered as a southeastern extension of Alborz Mountains (Lammerer et al., 1983; Eftekhar-Nezhad & Behroozi, 1991; Alavi, 1992; Seyed-Emami & Schairer, 2011). Jurassic successions, which have very well extended outcrops in the eastern Alborz and Binalud Mountains, were the main topic of the publications by Seyed-Emami & Schairer (2010), Wilmsen et al. (2009a,b), Raoufian et al. (2011, 2014), Seyed-Emami and Raoufian (2017), Seyed-Emami et al. (2018). Dalichai Formation in the eastern Alborz and Binalud Mountains comprises a thickness of marl and marly limestone, with an abundance of ammonite fauna which is the most important characteristic of the formation in the Binalud Mountains. This fauna in the Alborz and Binalud has long been considered in different papers (e.g., Shafeizad et al., 2005; Seyed-Emami et al., 2008, 2013, 2015, 2018; Raoufian et al., 2011, 2014). In this research, an outcrop of Dalichai Formation in the Bāghi stratigraphic section, northwest of Esfarayen city, was lithostratigraphycally and biostratigraphically studied.

The base of the measured stratigraphic section is located in 37°11′45.34″ and 57°16′21.89″, 29 km northwest of Esfarayen city (Esfarayen to Jajarm route). After field studies, reviews of lithofacies in the field, and drawing the log, 540 in situ ammonite specimens were obtained from the section. They are kept in the Museum of the Geology Department at the Ferdowsi University of Mashhad. The biometric details of ammonite specimens, including the dimensions of the specimens, size, depth, and diameter of the umbilical area, the number, arrangement, and shape of ribs, marginal keels, nodes, suture lines, and apertural shape, have been studied. The studied ammonitic fauna are typically Northwest Tethyan and belongs to the Submediterranean Province with episodic Mediterranean and Subboreal affinities (Seyed-Emami et al., 2013). It reflects the relationship between these regions with other parts of the Paleotethys sidelines during the Jurassic time.

In the Baghi section, the Dalichai Formation unconformably overlies the siliciclastic Shemshak Formation and gradationally underlies the cliff-forming carbonate rocks of Lar Formation. The Dalichai Formation, with a thickness of 655 meters, is divided into ten separate informal members and is mainly composed of marls, limestone, and marly limestone. One of the most important features of the Dalichai Formation in this section is the abundance of ammonite fauna, especially in the lower half of the section. Due to the specific color, lithology, and abundance of ammonite fauna, the second member is a key member.Paleontological studies in this research is led to the determination of 96 species, 26 subgenera, 39 genera, 20 subfamilies, 14 families, and 6 superfamilies belonging to 3 suborders of Ammonitida. According to the mentioned assemblage, 17 standard biozones are recognized, consisting of Grantiana, Parkinsoni, Zigzag, Retrocostatum, Bullatus, Gracilis, Anceps, Coronatum, Athleta, Lamberti, Transversarium, Bifurcatus, Bimammatum, Planula, Platynota, Hypselocyclum, and Acanthicum. These biozones show the age of late Bajocian – late Kimmeridgian for the Dalichai Formation. The studied ammonitic assemblages are closely related to the other Middle-Late Jurassic fauna from Iran and further peri-Mediterranean regions, which correlates with the Sub-Mediterranean province.

The Dalichai Formation is the first rock unit of the Middle Jurassic in the Alborz sedimentary basin that has occurred in a marine environment. The boundary of the Dalichai formation with Shemshak Formation is erosional unconformable while it is concordant with Lar formation. Due to lithological similarity, the boundary of the Dalichai formation with the Lar formation is unclear. It is also very difficult to identify the primary carbonates mineralogy, due to the effects of diagenetic processes solely on the basis of petrographic studies. We studied a section of Sharaf mountain with a thickness of 1420m and 149 samples was studied. The study of the major and minor elements, the Oxygen and Carbon isotopes, and plotting of these values against each other represents that the Dalichai formation have had original aragonite mineralogy, and the nonmarine diagenesis have had the highest impact on them. Plotting the Sr/Ca ratio versus Mn value, shows that these carbonates are affected in a semi-closed to open diagenetic system. Using Sr, Sr/Na, Sr/Ca, Oxygen and Carbon isotopes, the boundary of this formation with the Lar Formation is recognized in thickness of 1200m. The diagenetic environment temperature for this section limestones is 32.9ºC.

The Dalichai Formation in Darjazin section in NE Semnan with a thickness of 631 meters consisting of an alternation of bulish-gray was studied. This formation overlies the Shemshak formation disconformity with conglomerate bed and it has gradually been covered by the thick-beded limestones of the Lar formation. In order to study paleoenviroment of the Dalichai Formation the authors examined many different factors including Microfacies and palynological data (abundance and diversity of Dinocyst, proximate to chorat Dinocyst, palynofacies analysis and "selective preservation of organic matter"). A high percentage of brown wood and sporomorphs and the dominance of cavate and proximate dinocysts such as Nannoceratopsis gracilis, and pareodinia ceratophora and fluorescent amorphous organic matter, as well as Miliolid benthic foraminifera are evidence of suboxic to anoxic condition, which favored accumulation and preservation of organic matter in open marine lagoon, in the lower part of Dalichai Formation. A decrease in the brown wood and abundance and species richness of marine palynomorph (mainly chorate dinocysts) reflects more offshore settings in the upper part of Dalichai Formation. On the other hand, Appearance and increase of planktonic foraminifera and Radiolar and posidonia indicate development of strong marine transgression and deposition in an open marine environment.

The Middle and Upper Jurassic strata of the Alborz are named the Dalichai and Lar formations. The Dalichai Formation is introducing primary unites of Alborz Jurassic marine deposites and lithologically consist of a sequence of greyish limestones and marls that specially exposed in the south of Alborz Mountains. Most of the studies on the Dalichai Formation mainly focus on the ammonite fauna and their biostratigraphical importance (e.g. Seyed-Emami et al. 1985, 1989, 1995, 2013, 2015; Seyed-Emami and Schairer 2010, 2011a, 2011b; Dietze et al. 2014; Seyed-Emami and Raoufian 2017, Majidifard 2003, 2015; Schairer et al. 1991 and Raoufian et al. 2014, 2019). Ammonites are the most important fossils in the Dalichai Formation, they are of fundamental importance in determining the age and conditions of its paleoenvironment. In most area of the Alborz, the Dalichai Formation has marl, marly limestone, spary and thin bedded limestone with intercalation of marl and marly shale. In the sections studied this Formation consists of marl, marly limestone, sandy limestone and limestone. The aim of this study is to give an overview of the Oppeliidae fauna of the Dalichai Formation in Northern Alborz. The family of Oppeliidae has a high frequency as one of the Bathonian and Callovian index families in Alborz (e.g. Seyed-Emami et al. 2013). In the studied sections, this family has a frequency of 21.5%.

Lithostratigraphy and biostratigraphy of Middle Jurassic Dalichai Formation in Northern Alborz ranges have been studied for the first time. Three stratigraghical sections of Dalichai Formation in Northern Alborz ranges include Keriush in south of Babol, Kanefejar in south of Babol and Vana in Haraz road have been chosen for the paleontological studies. After field studies due to the abundance and importance of ammonite fauna in these sections, detailed sampling of ammonite fauna within the layers was done. After cleaning and preparing the ammonite samples and taking photograph of them, these samples were identified up to the species level and based on the international standard zonation (Cariou & Hantzpergue, 1997); zones of ammonites have been identified.

The studied ammonites come from three localities in northern Alborz Mountains. These are: 1. Keriush: 65 km south of Babol (N 36° 2'53.61", E 52°40'22.23"). The thickness of the Dalichai Formation at this section is 21/3 meters and can be subdivided into four members. The age of the Dalichai Formation is Upper Bajocian to Upper Callovian. 2. Kanefejar: 60 km south of Babol (N 36° 3'15.59", E 52°36'26.74"). The thickness of the Dalichai Formation is measured at this section 18/9 meters and can be subdivided, from bottom to top, into four members. The age of the Dalichai Formation is Upper Bajocian to Upper Callovian. 3. Vana: 75 km south of Amol (N 35°56'31.48", E 52°15'40.36"). The thickness of the Dalichai Formation is 70 meters and can be subdivided into four members. The age of the Dalichai Formation is Upper Bajocian to Upper Callovian. In this region, Dalichai Formation follows discontinuously on the dark, siliciclastic Shemshak Formation and is overlain gradationally by the light and cliff-forming carbonates of the Lar Formation. The biostratigraphy of the Dalichai Formation is discussed with special emphasis on the ammonite fauna (Oppeliidae family).

Palaeobiogeographically the middle Jurassic ammonite fauna in this area is closely related to that of the northwest-Tethyan, with relations to Subboreal / Submediterranean provinces. The study of ammonite fauna in this region led to identification of 48 genus, 18 subgenus and 26 species. Existing ammonite fauna indicates 8 ammonite biozones and Late Bajocian-Late Callovian ages for Dalichai Formation in Northern parts of Alborz ranges. The thickness of the formation in Northern parts of Alborz represents a much lower thickness of this formation than the southern parts of Alborz. The thickness changes of the Dalichai Formation in the northern and southern parts of the Alborz Mountains can be due to the tectonic conditions of the area and the existence of an extensional phase during its formation.

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.

The Dalichai Formation in Darjazin section in NE Semnan with a thickness of 631 meters consisting of an alternation of bulish-gray was studied.This formation overlies the Shemshak formation disconformity with conglomerate bed and it has gradually been covered by the thick-beded limestones of the Lar formation. Based on the presence and stratigraphic distribution of the most dominant miospore, Klukisporites variegatus and Callialasporites dampieri of pollen areidentified in the Dalichai (late Bajocian - Callovian) and Presence of some index dinoflagellate species led to identification of three 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 to middle Callovian). This biozonation corresponds largely to those established in Northwest Europe and Northwestern Tethys and reveals the marine connection between North of Iran with Northwest Europe and the Northwestern Tethys during the Middle Jurassic.

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.

Diverse and well-preserved palynofloras dominated, by land-derived palynomorphs (miospores) in association with marine entities such as dinoflagellate cysts, scolecodonts, foraminiferal test linings, and acritarchs (sensu lato) occur in surface samples of the Dalichai Formation, at the Pol Dokhtar stratigraphic section, central Alborz. Stratigraphic distribution of the dinocysts at the Pol Dokhtar stratigraphic section lead to the introduction of three successive biozones i. e. , Cribroperidinium crispum Total Range Biozone (late Bajocian), Dichadogonyaulax sellwoodii Interval Biozone (Bathonian to early Callovian), Ctenididinium continuum Interval Biozone (early to middle Callovian) and Subzone a (early to middle Bathonian). Furthermore, presence of such index late Bajocian species of dinoflagellate cysts as Meiourogonyaulax valensii, Cribroperidinium crispumin association withCarpatodinium predae (early to middle Bathonian) and Ctenidodinium combazii (Bathonian to early Callovian) suggests a Middle Jurassic (late Bajocian - Callovian) age for the host strata. Quantitative analysis of the palynological and palynofacies elements indicates low sedimentation rate in a relatively deep, low-oxygenated marine environment with decrease of the depth.

The Dalichai Formation is represented by greenish-grey color shales, calcareous shales, marls, and richly ammonitiferous limestones (Steiger, 1966), being widely distributed in the Alborz Mountain, northern Iran. It disconformably overlies the dark, siliciclastic coal bearing Shemshak Formation and underlies gradually by the light colored, more uniform Lar Limestone containing chert concretions. The Dalichai Formation is represented the first rock unit of the Jurassic marine sediments of the Alborz Mountain. This Formation includes a diverse fauna as ammonites, belemnites, bivalves, brachiopods, echinoderms, sponges, 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 presence of shale and marl layers, this formation has been the subject of many palynological studies. (such as 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 purpose of this study was to determine the palaeoenvironmental interpretation of the Dalichai Formation based on inferred palaeoecological preferences of dinocyst types, and quantitative analysis of the palynofacies in the Dalichai Formation at the Guydagh section, southeastern Maragheh.
Material and Totally 23 palynologically possible samples collected from the Dalichai Formation at Guydagh section, southeastern Maragheh. All samples were prepared following standard palynological processing procedures (Phipps & Playford, 1984), including HCl (10-50%) and HF (40%) utilized for dissolution of carbonates and silicates, respectively. Then the residues were saturated with ZnCl2 solution (specific gravity 1.9 g/ml) for density separation. All the residues were sieved with a 20 μm mesh sieve previous to making strew slides. Three slides for each preparation were examined by transmitted light microscope.
For quantitative study of the prepared slides, 15 field views were randomly selected from each slide and studied with a 16 - microscope magnification lens. The particles were counted for each sample to determine palynodebries and palynofacies. An analysis of facies including identification of palynomorphs, plant remains and amorphous particles, ratios of different particles, their size range in determination the paleoenvironment is highly important. Three main parameters including percentage of palynomorphs, phytoclasts, and organic matter (AOM) were transferred to Tyson triple diagram (Tyson 1993) for plotting and interpretations.
Discussion of Results and Diverse and moderately preserved palynofloras of marine and terrestrial derivation occur in surface samples of the Dalichai Formation Guydagh stratigraphic section in the southeast of Maragheh, western Alborz, northwestern Iran. In order to determine the age and reconstruct the paleoenvironment of the study section (including 198 meter of limestone, calcareous shale, marl and shale) was selected and examined palynologically.
The palynofloras comprise dinoflagellate cysts, miospores (spores and pollen grain), acritarchs, scolecodonts, fungal and algal spores. The palynological investigations led to recognition of 85 species of dinocysts belong to 43 genera. Based on recorded dinocyst assemblages, especially marker species, three palynozone including Cribroperidinium crispum Total Range Zone (late Bajocian), Dichadogonyaulax sellwoodii Interval Zone (Bathonian – early Callovian) and Ctenidodinium continuum Interval Zone? (late Callovian) and one subzone (subzone "a" from early to middle Bathonian) were identified.
The high similarity of western Alborz dinoflagellate assemblages with assemblages recorded from different parts of Iran (such as central and eastern part of Alborz and Binalud) and other parts of world (northwest of Europe, China, Qatar, Canada, Denmark, Egypt and etc.) proved presence of seaway connections between the mentioned basins through the late Bajocian - late Callovian.
Also based on the palynofacies studies, four palynofacies of Tyson (1993) (II, IVa, VI, IX) were determined that proposed domination of a dysoxic shallow marine environment throughout the sedimentation of Dalichai Formation. Palynological evidence such as high frequency of proximate dinocysts to chorate forms; the high proportion of the equidimensional opaque palynomaceral to the blade-shape opaque palynomaceral; the high ratio of phytoclasts to marine palynomorphs, and the abundance of transparent amorphous organic matter in comparison to the opaque amorphous organic matter, all indicates that the Dalichai sediments, accumulated in a dysoxic shallow marine environment at the Guydagh section, southeastern Maragheh.

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 Dalichai Formation at the Guydagh stratigraphic section in the southeast of Maragheh, (Western Alborz), with measured thicknesses of 198 meters (consisting of limestone, Calcareous shale, shale limestone, shale and marl) contain terrestrial (spores and pollen grains) and marine (dinoflagellate cysts, acritarchs, foraminiferal test linings and scolecodont) palynomorphs. This assemblage is formed from diverse and moderately-preserved palynomorphs. The recognized palynofloras includes 16 species of spores (assigned to 14 genera) and 19 species of pollen grains (belong to 11 genera). Based on presence of Klukisporites variegatus, Klukisporites Zone and Klukisporites variegatus Subzone are identified and assigned to the Middle Jurassic (late Bajocian - Callovian) in age. Comparing obtained data from this study and data gained from Dalichai equivalent sediments in Iran (Central and Eastern Alborz, Central Iran and Kopet Dagh geological zones) and other parts of the world (Australia, Afghanistan, Egypt, China, India and etc.), resulted similar climates (mild to warm and humid) during Middle Jurassic (Dogger) in these areas (due to similar vegetation). Based on recognized miospores and their frequency, Conifers, Pteridospermophyta, Pterophyta, Ginkgophyta, Lycophyta and Cycadophyta formed Dalichai vegetation at the studied section. The presence of warm water dinoflagellates such as Gonyaulacysta jurassica, Ctenidodinium continuum and Nannoceratopsis pellucida with fungal and algal spores confirmed the domination of warm and humid climate.