فصلنامه پژوهش های چینه نگاری و رسوب شناسی
سال سی و هفتم شماره 4 (پیاپی 85، زمستان 1400)

Abstract
In order to identify the palynofacies and to reconstruct the paleoenvironment of the Lower Cretaceous depositions in the Kopet-Dagh sedimentary basin, the Sanganeh Formation was sampled and studied. The four sections of the Sanganeh Formation were selected for correlation and comparison in the east and the center of the Kopet- Dagh Basin, respectively included Karizak, Mozduran, Sanganeh and Qarah-Su. The study of slides was done with an optical microscope. Marine palynomorphs groups, phytoclasts, amorphous organic matter, transparent to opaque amorphous organic matter ratio, brown to opaque phytoclast ratio, Peridinioid to Gonyaulacoid dinocyst ratio, abundance, and diversity of marine palynomorphs and dinoflagellates were counted and investigated.  In this study, a quantitative analysis of the main palynologic elements (AOM, marine palynomorph, phytoclast) led to characterize four palynofacies types that were identified in the Karizak and Mozduran sections. Based on the palynofacies analyses and according to the plotting to Tyson diagram, we have recorded an increase in the number of phytoclasts and a decrease in the number of marine palynomorphs to the east indicating a decrease in the depth and oxygen trend in the Sanganeh Formation in these part of the Kopet-Dagh sedimentary Basin. The sedimentation rate of the Sanganeh Formation was also considered low in the studied sections.
Keywords: Palynofacies, Dinoflagellate, Kopet-Dagh, Sanganeh Formation, Lower Cretaceous
 
 
According to Tyson (1993, 1995) and Batten (1996b), identification of palynofacies plays an essential role in determining depositional environments as well as studying the petroleum potential in sediments. The components of palynologic slides, which are used to determine palynofacies and paleoenvironmental interpretation, can be grouped into three groups: amorphous organic matter (AOM), marine palynomorphs (MP), and phytoclasts (P).  Due to the Sanganeh Formation lithology, paleontologists have been interested in working the shale samples. Several studies have been done to determine the age and identify the paleoenvironment on this formation in the Kopet-Dagh basin based on different fossil groups including foraminifera, calcareous nannofossil, ammonite, and palynomorph. Four stratigraphic sections have been selected from the Sanganeh Formation in the Kopet-Dagh Basin. The studied sections from the east to the center of the Basin are included Karizak, Mozduran, Sanganeh and Qarah-Su, respectively with a thickness of 320, 355, 550, and 580 meters. In the studied sections, the lower and upper boundaries of the Sanganeh Formation are continuance with Sarcheshmeh and Aitamir formations. The aim of this study was to identify the palynofacies and the paleoenvironment of the Sanganeh Formation based on the counting and frequency of palynological content in the studied sections.
 
Material & Methods    
A total of 370 samples were taken from the Sanganeh Formation in four sections, (Karizak, Mozduran, Sanganeh, and Qarah-Su). Samples were prepared based on the acid treating technique (HCl/HF) (Travers 2007). In this standard method, dry sediment samples were degraded with 30% hydrochloric acid (HCl) and 40% hydrofluoric acid (HF) to extract acid-resistant organic matter. These acids had been added to remove carbonates and silicates materials. In the following steps, after sieving (10 µm mesh), the samples were centrifuged with heavy liquid zinc chloride (ZnCl2), and the residual material was finally transferred to 3–5 lamellas for palynological studies. It should be noted that the samples were not oxidized.
 
Discussion of Results & Conclusions  
Based on the relative frequency of three palynological matter categories, three types of palynofacies are recognized at the Qarah-Su section,and four types of palynofacies at the Karizak and Mozduran sections. According to these plots, we could subdivide the Sanganeh Formation into two parts in the studied sections. The first part is characterized by abundant phytoclast matter indicating a highly proximal dysoxic-anoxic basin.while the second part of the studied succession shows a change in organic matter in the samples composed of AOM and marine palynomorphs. This part is indicated by the proximal suboxic-anoxic shelf. The depositional depth showed an increase in this part. However, an exception could be observed in the Karizak section so there could be a third part and we could have observed a decrease in the depositional depth again.
The relative abundance of marine palynomorphs, phytoclasts, and amorphous organic matter, the ratio of transparent/opaque amorphous organic matter, brown/opaque phytoclast and Peridinioid/Gonyaulacoid dinocyst, and also the density and diversity of marine palynomorphs and dinoflagellates were considered at this study. The ratio of the  transparent AOM to opaque AOM indicates low oxygen conditions have fluctuated over time. The absence of dinocysts at the base of succession may be due to the lack of preservation of distributed organic matter at the sediment surface, diagenesis, or the initial lack of production of dinoflagellate cysts in the marine environments (Ogg 1992). The upward trend in the peridinioid group is also considered to be near-coastal or transitional environments (Habib and Miller 1989).
The distribution of palynological data on the Tyson diagram indicates the relative high amount of phytoclasts for this formation, especially in the eastern sections of the Kopet-Dagh Basin. According to the diagrams, the shallowing trend to the east can be observed, clearly in the Karizak section. Therefore, the depositional environment of the Sanganeh Formation can be considered as a shallow, coastal, and low oxygen environment in the eastern part of the study area. Towards the center of the Basin, the amount of marine palynomorphs has increased which indicates deeper and distal coast, and a relatively lack of oxygen.
The paleoenvironmental and palynological elements analysis of the Sanganeh Formation in the studied area generally show the following Comparison of the three main groups of palynological components (phytoclasts, amorphous organic matter, and marine palynomorphs) in the studied sections shows that the amount of phytoclasts in all sections is almost high. The amount of amorphous organic matter and marine palynomorphs are in the next degree of abundance. Due to the relative amount of these three groups, the base of the Sanganeh Formation has shown the shallow marine deposit and proximal setting. In the middle part, the amount of organic matter is increased and the amount of phytoclasts is reduced. The amount of marine palynomorphs also shows a relative increase in this part.
Therefore, the increase in amorphous organic matters, the presence of marine palynomorphs, and the relative decrease of phytoclasts, palaeoenvironment of the sequences can be considered mud dominate distal shelf. The upper part of the studied sections, which can be seen just only in the Karizak section, indicates a decrease in depth and near-shore environments, accompanied by an increase in phytoclasts.
The Karizak section, which is the most eastern section, has the lowest marine palynomorphs and the highest phytoclasts. The Mozduran section, which is the second section from the east shows  an increase in the marine palynomorph and AOM. Finally, marine palynomorphs and AOM are increased in the Sanganeh and Qarah-Su sections,indicating an increase in depth and a decrease in oxygen to the center of the Kopet-Dagh basin.

Abstract
Plant macrofossils from the Shemshak Formation, Rudbar, western Alborz, collected at two distinct horizons, including horizon 1 (Koushk area) and horizon 2 (northern Rudbar), are examined to determine the relative age and sedimentary environments of the host strata. The assemblage includes 32 species (distributed among 22 genera) of plant macrofossil; variably preserved petrified wood could also be found in some of the studied samples. The Horizon 1 consists of siltstones and shales. Horizon 1 consists of siltstones and shales is dated to the Late Triassic (Rhaetian?)–Early Jurassic based on the known stratigraphic ranges of various taxa.  It is comparable with the Shemshak–Ashtar zones in the Shemshak area, the lower floral zone of Noor valley, and floral zone A of central Alborz. Representatives of cycadophytas, coniferophytes, pteridophytes, and sphenophytes dominate the assemblages examined. The contemporaneous coastal vegetation apparently flourished in a vast coastal plain, under a warm climate. Horizon 2 comprises alternation of sandstones, siltstones and shales with few coal seams includes coniferophytes, cycadophytes, ginkgophytes, sphenophytes, and filicophytes. This assemblage suggests the Liassic–Middle Jurassic (Aalenian)? age that is comparable with the Shemshak–Ashtar zones, up to the lower part of Vasekgah of Shemshak, floral zone A–C (partial) of central Alborz, and plant zones II–III of eastern Alborz. The sediments that host plant macrofossils of the horizon 2 seemingly accumulated in river systems and probably under temperate-warm climate with variable humidity of this plant assemblage, Cladophlebis roesserti, Otozamites parallelus, Ginkgoites yimaensis are recorded for the first time from Iran.
Keywords: Plant macrofossil, Shemshak Formation, Late Triassic (Rhaetian), Early Jurassic, Western Alborz.
 
 
 
As a result of the Early Cimmerian tectonic event, Iran is divided into two geologically independent zones; one in the northeast (comprising central Iran, northern and northeastern Iran) and the other in the southwest (Zagros area) of the country. These two distinct sedimentary-structural zones include the Jurassic strata of notably variable lithofacies and biofacies complexion. The Jurassic deposits in the former zone are represented by a single sedimentary cycle known as the Shemshak Group (a.k.a. Shemshak Formation) bounded by two unconformities. The rock unit and its equivalents in the Alborz Ranges and central Iran (especially around Kerman and Tabas) include coal layers/seams, thus extensively investigated by both geologists and paleobotanists. The study of plant macrofossils not only affords information about the past plant communities, their temporal/spatial distribution and their evolution but also allows for the palaeoecological and palaeoclimatological inferences.
Notably, thick exposures of the Shemshak Formation widely distributed in the vicinity of Rudbar (36˚32 ́ - 37˚7 ́N, 49˚ 11 ́-50˚ 05 ́), south of Gilan Province (western Alborz), comprise mainly alternation of dark green sandy, locally coal-bearing black shales, gray-green siltstones and sandstones, and thin intercalations of limestones (Aghanabati 1998). The upper and lower contacts of the rock unit at this locality are both faulted against the Eocene–Quaternary and Triassic strata, respectively. The rich, diverse, and reasonably well-preserved plant macrofossils sporadically occurring in the Shemshak Formation especially at two distinctive horizons; horizon 1 (Koushk, south of Rudbar) and horizon 2 (north of Rudbar) are examined to derive biostratigraphical and palaeoecological inferences.
 
Material & The plant macrofossils elaborated upon herein, 320 rock samples, are collected from outcrops of the Shemshak Formation around Rudbar, western Alborz. The specimens occur as reasonably preserved impressions on bedding surfaces of shales and fine-grained sandstones. All of the samples collected and used in the current study are housed in the Palaeontology Collection, Kharazmi University, Tehran, Iran.
 
Discussion of Results & Horizon 1 (Koushk area), consisting of siltstones and shales, includes plant remains representing sphenophytes, filicophytes, cycadophytes and coniferophytes. The most diverse taxa in this assemblage, in an descending order, are ferns, conifers, sphenophytes, and cycadophytes. Based on the known stratigraphic ranges of such various species as Ctenis, Clathropteris, Equisetites, Neocalamites, a Late Triassic (Rhaetian?) –Early Jurassic age is suggested for the host strata. The latter accumulated in a vast coastal plain under a warm, moist climate with adjacent highlands drained by rivers. The plant macrofossils occurring in horizon 1 generally seem comparable with those retrieved from the Kalariz (partial) and Javaherdeh formations of northern Alborz.
Horizon 2, occurring in the Shemshak Formation of northern Rudbar, comprises alternation of sandstones, siltstones, shales as well as few coal seams and limestones intercalations. The horizon includes various representatives of sphenophytes, filicophytes, cycadophytes, coniferophytes, ginkgophytes, and petrified wood specimens. The plant macrofossils collected from this interval, Cladophlebis roesserti, Otozamites parallelus, and Ginkgoites yimaensis are reported for the first time from Iran. Horizon 2 can be divided into three units (A, B, C) based on the relative abundance of the plant macrofossils. Unit A is characterized by, in ascending order of abundance, Marattiopsis, Cladophlebis, and Podozamites. In unit B, preceding unit C, Podozamites, Cladophlebis, Nilssonia, Pterophyllum, Ginkgoites, Phlebopteris, Anomozamites, Otozamites, Baiera, and Pagiophyllum occur in an ascending order of profusion. Unit C is differentiated from unit B by the exclusive occurrence, in the former, of Annulariopsis and Coniopteris. The plant macrofossil assemblages of horizon 2 indicate an Early–Middle Jurassic (Aalenian)? age for the host strata. This horizon seems comparable with the plant fossil assemblages previously reported from the Javaherdeh Formation of northern Alborz, Shemshak–Ashtar zones, the lower part of Vasekgah of Shemshak, Floral zone A–C (partial) of central Alborz,  and Plant zones II, III from eastern Alborz. The host strata of horizon 2 seemingly accumulated in a sizeable river system and probably under temperate-warm climate and variable humidity.

Abstract
This study investigates the effect of facies and diagenesis on the pore-throats in 110 m of carbonate rocks of the Dariyan Formation from one well in the central Persian Gulf. A total of 390 thin sections and 160 core porosity and permeability data were investigated. Petrographic studies led to the identification of nine microfacies in five sub-environments deposited in a carbonate ramp platform. The most important identified diagenetic processes include micritization, cementation, compaction, fracturing and neomorphism that affected the sediments of the Dariyan Formation during different stages of marine, meteoric and burial diagenetic environments. The Winland number has been calculated and compared with measured pore throats. Comparing the Winland rock types with microfacies, it is concluded that two microfacies of laminated mudstone and orbitolina wackestone have the smallest pore-throats (R35< 0.1 µµ). This is due to mud-dominated texture, presence of micrites, presence of clay minerals blocking the pores, and compaction and cementation. In contrast, bioclast peloid packstone to grainstone of shoal environment, due to the grain-dominated texture, low micrite abundance and open fractures, have the highest pore-throats (0.5<R35< 1 µ) among the total microfacies. In some samples, cementation and compaction have reduced the pore-throats and transferred them to units with a value of R35 between 0.1 to 0.5 µ. The upper Dariyan and lower Dariyan contains the microfacies with large (R35> 0.5 µ) and medium (R35> 0.5> 0.1 µ) pore-throats and have the best reservoir quality. In contrast, the Hawar Member corresponds to microfacies with a smaller pore-throats (R35> 0.1 µ) and has almost no reservoir quality.
Keywords: Dariyan Formation, Microfacies, Diagenetic, Pore-throats, Winland diagram
 
 
Porosity and permeability are two important parameters in identifying and understanding the behavior of an oil reservoir. These two parameters show many changes in the shallow carbonate reservoirs (Moore 2001; Lucia 2007). Rock types divide the reservoir rocks into separate units based on similar properties such as permeability and porosity. There are different ways to classify the rock types. The Winland method (Winland 1972) is one of the most widely used approaches for determining these rock types. The method is based on the Winland empirical equation which expresses the relationship between porosity, permeability, and pore-throat sizes at 35% mercury saturation in mercury injection capillary pressure (MICP) test. The diversity of microfacies and the effects of diagenesis, determined the pore-throat sizes and resulted Winland number. Therefore, it is important to study the geology of carbonate reservoirs and the impact of facies and diagenesis on the pore-throat sizes. This study, after examining facies and diagenesis, determines the impact of these two factors on the pore-throat size distribution in the Dariyan Formation. The results could show the most important factors affecting the distribution and changes of the pore-throat sizes in the carbonate rocks of this formation.
 
Materials & In this study, 110 meters of carbonate rocks of the Dariyan Formation in a well from a field in the central part of the Persian Gulf have been studied. At first, petrographic studies were performed using a polarizing microscope (on 390 thin sections) and the facies were named after the Dunham classification method (Dunham 1962). Flügel classification (Flügel 2010) was used to determine the sedimentary environments of the microfacies. Then, the diagenetic processes were investigated. Porosity and permeability of 160 plug samples were measured using Boyle and Darcy methods, respectively. Winland formula has been used to calculate and classify the pore-throat sizes of the samples. At last, the effects of microfacies and diagenetic processes on pore-throat sizes have been investigated through porosity-permeability diagrams and statistical calculations. To check the pore throats using the Winland R35 method, it is necessary to ensure a good correlation between the values of R35 calculated through the experimental formula of Winland using the porosity-permeability values and the actual values of R35 determined by the mercury curves.
 
Discussion of Results & Facies analysis led to the identification of nine microfacies in five sub-environments deposited in a carbonate ramp platform. Micriticization, bioturbation, cementation, especially calcite cement, compaction (physical and chemical), neomorphism and fracturing are observed in the studied formation. These diagenetic processes affected the sediments of the Dariyan Formation during different stages of marine, meteoric and burial diagenesis. Petrographic studies do not show high porosity, but core tests show considerable porosity in these samples. This confirms the presence of microporosity as the main type of porosity in the samples. To investigate the effects of facies and diagenesis on the pore-throat sizes, porosity and permeability data were plotted on the Winland diagram. According to the Winland method, three zones with different pore-throats (R35< 0.1 µ, 0.1 <R35< 0/5 µ, 0.5<R35< 1 µ) were identified. The Winland number has been calculated and compared with measured pore throats. The results show an acceptable correlation between the measured pore throat values and the calculated pore throats. Zone 3 (0.5<R35< 1 µ) shows the best reservoir quality. Comparing the Winland rock types with microfacies, it could be concluded that two microfacies of laminated mudstone (MF1) and orbitolina wackestone (MF3) have the smallest pore-throats (R35< 0.1 µ). This is due to mud-dominated texture, the presence of micrites, the presence of clay minerals that block the pores, compaction and cementation. Bioclast wackestone (MF2) microfacies deposited in lagoon environment have the highest frequency in units with a value of 0.1> R35 µ. Two microfacies of MF5 and MF8 with average pore-throats have the highest frequency in units with a value of 0.5<R35< 1 µ. In contrast, bioclast peloid packstone to grainstone of shoal environment, due to the grain-dominated texture, low micrite abundance and open fractures, have the largest pore-throats (0.5<R35< 1 µ) among the total microfacies. Cementation and compaction have reduced the pore-throats of some samples and moved them to units with a value of R35 between 0.1 to 0.5 µ. The upper Dariyan and lower Dariyan contain the microfacies with large (R35> 0.5 µs) and medium (R35> 0.5> 0.1 µs) pore-throats and have the best reservoir quality. In contrast, the Hawar Member corresponds to microfacies with smaller pore-throats (R35> 0.1 µs) and has almost no reservoir quality. MF6 and MF9 have various pore-throat sizes due to the effect of different diagenetic processes and could be observed in all three zones.

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.

Abstract
The thick Jurassic fluvial coarse-grained sediments rest non-conformably on older metamorphic rocks to the northwest of Mashhad. Two sections, 300 and 400 m thick, were measured and studied through the Jurassic deposits.  In this unit, three facies assemblages, conglomerate, sandstone and shale, have been identified. They comprise eight lithofacies (Gcm, Gmg, Gmm, Sm, Sh, Sp, Fl, and Fm) and four architectural elements (Channel-fill element (CH), Sediment gravity flows (SG), Downstream–accretion element (DA), and Overbank fines (FF)). The orientation of the gravel particles indicates that the direction of the paleo-flow was from northeast to southwest. The presence of an erosive base, lens-shaped sediment bodies, and fining-upward sequences suggests a gravelly braided-river system that  deposited in a half-graben. Based on the results of petrological studies, subarkose, arkose, lithic arkose, sublitharenite, and litharenite are the main identified sandstone petrofacies. Also, based on the components of the sandstones, plutonic and metamorphic rocks have been identified as the source of sediments deposited in a humid climatic condition. In addition, the grain types suggest recycled orogen (RO), craton interior (CI), dissected arc (DA), and transitional continental (TC) tectonic settings of the study area during deposition.
Keywords: Conglomerate, Braided river, Paleotethys, Jurassic, Binalud, Iran
 
 
The Binalud Mountains form one of the most characteristic geological zones in northeastern Iran. Stöcklin (1968), Eftekhar-Nezhad and Behroozi (1991), and Alavi (1992) considered the Binalud Mountains as the continuation of the Alborz Mountains, but Nabavi (1976) interpreted them as an incremental unit between the Alborz and Central Iran based on the similarity of the Palaeozoic succession with that of Central Iran, and the similarity of the Jurassic and Cretaceous strata and of its folding style with the Alborz mountains. The Binalud Mountains consist mainly of sedimentary, igneous, and metamorphic rocks, among which Jurassic sediments have been deposited in many areas, resting unconformably on Palaeozoic and/or Triassic sedimentary and metamorphic rocks. According to the position of the strata and sparse biostratigraphic data, an Early to early-Middle Jurassic age is suggested for the study deposits (Wilmsen et al., 2009a). The purpose of the present study is to figure out the identification of lithofacies and interpretation of their depositional environments. In addition, the source rocks (possibly hidden or eroded) of the Jurassic siliciclastic rocks (NW of Mashhad), and the tectonic setting of the Binalud Mountains during deposition of this formation are evaluated based on petrographic analysis.
 
Material & Two sections (400 and 300 m thick) to the northwest of Mashhad were measured and sampled. In total, 200 samples of sandstone and conglomerate were collected. Twenty-three samples of sandstones and 20 conglomerates were selected for thin section preparation. Petrographic modal analyses were made using a Nikon Eclipse E400 polarizing microscope, with 500 point counts using the Gazzi-Dickinson method at the Islamic Azad University of Mashhad, Iran. Sandstones were classified following Folk (1980), and coarse-grained sediments were classified based on the Pettijohn classification (Pettijohn, 1975). A facies code modified from Miall’s (1996) classification was utilized, with G for conglomerate facies, S for sandstone facies, and M for mudstone facies. To measure paleocurrents, 695 imbricated clasts from conglomerate were measured in two sections and plotted on a rose diagram.
 
Discussion of Results & The Jurassic deposits in the study area are all siliciclastic and range in grain size from clay to pebbles. Based on field and laboratory studies, three facies assemblages, conglomerate (Gcm, Gmg, Gmm), sandstone (Sm, Sh, Sp), and shale (Fl, Fm) have been identified. Architectural elements are defined as CH, SG, DA, and FF. The paleoflow direction is consistent with the palaeoreconstructed position of the Jurassic deposits and indicates that sediment was transported from northeast to southwest.
The lack of any marine fossils and the abundance of plant fossils in the finer-grained parts clearly point to a non-marine setting. The conglomerates and pebbly sandstones can be interpreted as the fills of braided river channels in an alluvial fan system (Wilmsen et al. 2009a; Poursoltani et al. 2015, Poursoltani and Fursich 2020). Medium to coarse-grained sandstones with planar lamination and occasional trough cross-stratification can be interpreted as part of fluvial channel fills deposited during times of waning flow velocity. Fine to very fine-grained sandstones, some with plant fragments, interbedded with siltstones and mudstones represent overbank sediments. The mudstones and shales are floodplain deposits.
Petrographically, the sandstones are fine to medium-grained and grain-supported, with some coarse-grained and well-rounded components. Based on Folk’s classification (1980), the sandstones are predominantly subarkose, arkose, lithic arkose, sublitharenite, and litharenite. Based on the petrographic analysis of the Jurassic sandstones, plotted on the diagrams of Dickinson et al. (1983) and Yerino and Maynard (1984), craton interior, recycled orogen, quartzose recycled, mixed zone, and transitional continental are the main tectonic settings of the studied sediments. Basu’s diagram (Basu et al., 1985, with Qp, Qm u, Qm, nu) indicates that metamorphic rocks were the main source area of the deposits. In the Q–F–R ternary diagram of Suttner et al. (1981), the Jurassic sandstones plot in the field for plutonic and metamorphic source areas under humid climate conditions.
According to previous studies (Wilmsen et al., 2009a; Sheikholeslami and Kouhpeyma 2012) and the result of this study, the non-marine Jurassic succession was possibly related to the early Middle Jurassic Mid-Cimmerian Tectonic Event. Thus, we suggest that the Jurassic strata of the Binalud Mountains were deposited in a half-graben. This graben formed within the Cimmerian mountain belt and developed during a late phase of the Early Cimmerian Orogenic Event

Abstract The Early Cretaceous succession in the southern part of Yazd Block begins with terrestrial sediments of the Sangestan Formation. Little attention has been paid to this formation and most studies have focused on its lithostratigraphy. In this study, some geochemical studies have been performed on this formation. Twenty seven siliciclastic samples were taken from the Sangestan Formation in two sections of Bidakhvid and Alavi Mountain in order to identify the type of siliciclastic sediments, the nature of the sediments, and palaeoclimate conditions. Mineralogical studies and modal analysis showed that the siliciclastic sediments have been classified as sandstone (arkose) and siltstone. The results of factor and cluster analysis depicted that the chemical composition of siliciclastic sediments is different in the study areas. Based on multivariate analysis, siltstones that have high positive values of Zr, V, U, Sc, Sr, REE, MgO, Fe2O3, TiO2, and CaO elements are related to cement, while sandstones showed high positive values for K2O, Na2O, SiO2, Al2O3 elements. The results showed that siltstone sediments have more calcite and iron cement than the sandstone samples. By studying the variations of these elements versus the profile of the Sangestan Formation, it was observed that the elements related to rock cement are concentrated in siltstones due to the increasing depth of the sedimentary basin or more extension related to rift event, and the entrance of new elements into the basin. Also, the results of weathering indices depicted that both rocks have been formed in the same climate conditions which is consistent with the palaeogeography of Yazd Block during the Early Cretaceous.Keywords: Sangestan Formation, Yazd Block, Geochemistry, multivariate analysis, sedimentary environment, weathering index  IntroductionThe Sangestan and Taft formations dating back to the Early Cretaceous were deposited in many locations of Yazd Block which is located in the western part of the Central–East Iranian Microcontinent.In general, most studies have focused on the Taft Formation because it hosts lead and zinc deposits such as Mahdiabad, Farahabad, Mansourabad, etc. (Mojtahedzadeh 2002; Maghfouri and Hosseinzadeh 2018; Maghfouri et al. 2019; Maghfouri et al. 2020). On the other hand, a few studies have been performed on the Sangestan Formation focusing on its stratigraphy and paleontology. Until now, the geochemistry of Sangestan sediments and their sedimentary environment have not been paid attention to.The use of major, trace, and rare earth elements of siliciclastic sediments is very common in sedimentary geochemistry studies used by researchers to identify various purposes, including the tectonic setting, palaeoweathering conditions of the source area, and the nature of the source rock (Shadan and Hosseini-Barzi 2013; Wang et al. 2013; Nowrouzi et al. 2014; Salehi et al. 2014; Zaid et al. 2015; Moallemi et al. 2017; Okon et al. 2017; Periasamy and Venkateshwarlu 2017; Somasekhar et al. 2018; Abubakar et al. 2019; Etesampour et al. 2019; Sci et al. 2019; Xu et al. 2019).Multivariate statistical methods have been utilized to determine the relationship between several elements and the nature of sediments; something impossible by univariate statistical analysis. Despite the advantage of multivariate statistical methods, they have not been paid considered in siliciclastic geochemistry and they have been used only in a few studies.The main purpose of this study is to evaluate the composition and petrography of siliciclastic rocks of the Sangestan Formation, the relationship between the composition of the sediments and the deepening of the sedimentary basin, the relation between the nature of the sediments and the major and trace elements by multivariate analysis, and the climate conditions in Yazd Block during the Early Cretaceous. Material & MethodsAfter field observation, sampling was performed from the Sangestan Formation at the Bidakhavid and Alavi Mountain sections. Seventeen samples (nine siltstone and eight sandstone samples) from Alavi Mountain and 10 samples (three siltstone and seven sandstone samples) were collected from Bidakhavid.Sixteen thin sections from siliciclastic samples were studied petrographically by the Olympus model polarizing microscope.  The point counting of more than 500 points per thin section was performed on twelve sandstone samples by the Gazzi-Dickinson method.Twenty-seven samples of siliciclastic rocks of the Sangestan Formation were selected for geochemical objectives. The preparation steps of the samples which include the cutting of the samples in order to obtain an un-weathered surface, crushing, and grinding to achieve the particle sizes under 200 mesh were performed at Yazd University. Then, the representative samples were analyzed by Zarazma Mineral Studies Company (Iranian company). To determine the major oxide elements, the samples were fused by lithium metaborate and dissolved in dilute nitric acid and, finally, determined by Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES). An ICP-OES 735 instrument in Australia was used to analyze the samples. Moreover, the rare earth elements (REE) and other trace elements were determined by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). The instrument used was an ICP-MS Agilent series HP 4500 in the United States.SPSS and GCDkit software were used to carry out multivariate statistical studies and to plot ternary diagrams, respectively. In addition, Rockwork 14 software was used to draw the stratigraphic column. Discussion of Results & ConclusionsThe preliminary study of thin sections showed that the siliciclastic samples of the Sangestan Formation include sandstone and siltstone in the two studied sections. Sandstone samples are often medium-grained, with a small percentage of coarse-grained, moderately rounded and immature. Modal analysis was performed on sandstone samples for more detailed studies. The main constituents are quartz grains (56% and rock fragments ( less than 1%), as well as feldspar (25%).Siltstone samples are similarly composed of quartz, feldspar, and rock fragments. They have about 52% quartz, most of which is monocrystalline, and only less than 1% is polycrystalline quartz. The amount of feldspar is less than sandstone samples and they constitute about 16% of the rock volume. Similar to the sandstone samples, a few rock fragments were observed in siltstone samples. Furthermore, on the basis of the classification of Folk (1980), sandstone samples of the Sangestan Formation showed arkosic composition.  This result was validated by geochemical data confirmed by the geochemical classification of Herron (1988).In factor analysis, the positive and large factor loadings demonstrate a significant correlation between the variable and corresponding factor in the matrix. The results of factor analysis identified two first factors which discriminated the elements associated with the main constituents of siliciclastic sediments and those  related to the cement of siliciclastic sediments.For example, factor 1 showed positive factor loadings with Zr, V, U, Sc, Sr, REE MgO, Fe2O3, TiO2, CaO and negative factor loading with Cr, Na2O, SiO2, and Al2O3.  This factor depicted that the cement of rocks was formed from carbonate, iron oxide, and so on whereas the main constituents of siliciclastic samples were formed from elements such as Na2O, SiO2, and Al2O3. Furthermore, the results of the hierarchical cluster analysis shown in the dendrogram confirmed those of factor analysis.In order to evaluate the changes of these groups of elements, they were plotted along the sedimentary log. The results showed that the elements which are associated with the framework constituents of siliciclastic samples are more in sandstone rocks than siltstone rocks. Conversely, the elements related to the cement of siliciclastic sediments are more in siltstones than sandstone rocks.  Thus, it can be interpreted that the time of siltstone deposition was probably accompanied by an increase in the depth of the basin and the presence of more cement in the basin. Finally, the results of (A-CN-K) Al2O3-(CaO*+Na2O)-K2O ternary diagram and diagram which was proposed by Suttner and Dutta (1986) depicted that these sediments have been deposited in arid to semi-arid climatic conditions.