Introduction: Loess studies have about 185 years of documented history. High agricultural suitability, sensitivity to erosion and archiving the climatic changes signals, make the loess deposits very interesting to study. Understanding the historical development and different aspects of loess sediments are necessary for further investigations on loess deposits.Methodology: Regarding the published studies on loess, this paper has been organized into five sections including: 1) definition and characteristics of loess, 2) history of world loess studies, 3) processes of silt production, 4) importance of loess deposits for PALEOCLIMATE studies and 5) investigations carried out on Iranian loess deposits and soils. Major references for each subject were reviewed. Results and Discussion: The word "loess" has been derived from the German word "L?s", meaning loose, which was used for the first time by Leonhard in 1824. Regarding the definitions of loess presented by many authors, aeolian origin and silt fraction dominance have been accepted as the two main characteristics of loess deposits. The particle size distribution is the most important characteristic, which is measured before any other properties. The common mineralogical composition of loess deposits is as fallows: quartz in the sand fraction and quartz, feldspars, carbonates, mica and heavy minerals in the silt fractions. Illite and smectite are dominant minerals in clay fraction. However, the mineral composition is highly related to the loess origin. For example, loess in Argentina contains a lot of glass and feldspars, while Spanish loess deposits contain anhydrite and gypsum because they have originated from volcanic ash and Tertiary formations, respectively. Furthermore, soil formation processes during interglacial periods might have caused mineral transformation. Loess was first identified by Leonhard in 1824. Lyell in 1833 attracted a lot of attention to loess deposits worldwide through his several reports. Determining the nature (aeoloan, alluvial or in situ genesis) and clarification of silt formation processes have been two main research subjects during this period. Berg (1916) suggested the in situ formation of loess; but Richtofen in 1882, many years before Berg, had proven the aeolian origin of loess deposits. Based on the close relationship between the major loess deposits areas and ice sheet regions, Tutkovskii in 1899 explained the role of glaciers in silt production. Even until recent decades, some researchers such as Smalley believed that glacial grinding was the main process having enough energy to produce quartz silt. Obruchev in 1945 divided loess into hot and cold loess and referred to factors except glacial grinding for silt production. Currently, based on the silt origin, loess deposits are grouped into four classes including glacial or periglacial loess, desert or peridesert loess, mountain or perimountain loess and non-typic loess. Quartz silt is the most common particle in loess deposits. In the early studies, much attention was paid to the close relation between extensive loess deposits and glacial and periglacial paleoenvironments, giving rise to the hypothesis that glacial grinding was the main silt generating mechanism. Identification of loess deposits in desert environments showed that there were mechanisms other than glacial grinding for quartz comminution. Salt weathering, frost weathering, aeolian abrasion, and fluvial comminution are responsible mechanisms for silt production. Nahon and Trompette (1982), Wright (2001) and Iriondo and Kr?hling (2007) believe that, on a global scale, the importance of glacial grinding for the production of silt is less than what was initially expected. The other important aspect of loess studies is based on the observations of Hardcastle in 1890 who related loess formation to climate changes. Up to now, research reports have shown that loess deposition and soil formation were active during the cold glacial and hot interglacial periods, respectively. The periods of loess deposition and soil formation are well correlated to marine isotope stages. This finding is the basis for PALEOCLIMATE reconstruction and landscape evolution. There are vast areas covered by loess deposits in northern Iran. The presence of loess deposits in other parts of the country, especially desert fringes, is expected. For example, loess deposits in southern Mashhad and in Persepolis basin have been recently identified. It is evident that the loess thickness in dry regions is much less than that in the north. In recent decade, diverse aspects of loess deposits from northern and other parts of the country have been studied. The results of these studies showed the overall correlation of loess deposition and soil formation between Iran and major loess areas of the world during last glacial-interglacial period. The most important findings are windy LGM (MIS2) and soil formation during MIS5. There are, however, many unknowns, which should be clarified in the future investigations.Conclusion: Loess is an aeolian silt-dominant sediment. Although it is believed that quartz and mica are the main mineral constituents, however, the mineral composition is highly related to the loess origin. Loess accumulation is a climate dependent phenomenon. The common argument is that loess deposition and soil formation were active during the cold glacial and hot interglacial periods, respectively. This fact makes the loess-peleosol sequences as a reliable archive of climate changes. The loess studies in Iran are limited and it is necessary to determine the loess distribution around the country and investigate their physical, chemical and mineralogical characteristics as well as their implication for PALEOCLIMATE studies

In the present study, in order to reconstruct the paleoenvironmental and climatic changes of Jiroft during the last 4000 years, several evidences of sedimentology and biogeochemistry on a sedimentary core have been investigated. Around. 3950 cal yr BP, low values of Ti/Al, Si/Al, C/N and CPI along with high values of δ13COM, and Paq indicate a wet period in Jiroft. evidence indicates a relative decrease in humidity between about 3900 and 3293 cal yr BP. Between 3293 and 2897 cal yr BP, Jiroft was dry and dusty. The results show very dry conditions with a significant increase in the amount of dust around 3200 cal yr BP. A long-wet period from about 2897 to 2302 cal yr BP can be recognized with high Paq values. The highest Ti/Al values along with the lowest δ13COM values indicate increased wind activity and dry conditions between 2100 and 1650 cal yr BP. Jiroft experienced wet conditions between 1540 and 1315 cal yr BP. With the relative decrease of rainfall, a semi-humid climate prevailed in Jiroft between 1315 and 854 cal yr BP.

Rock beds containing plant macrofossils of Norian in Alborz region belong to two stratigraphic units of Lalehband and Shahmirzad. The same beds in Kopeh-Dagh area belong to Mian-Kuhi Formation and in Central Iran belong to Qadir submember in Tabas region and Dehroud member in Kerman region. In general, plant diversity and vegetative cover during the Norian stage is less than Rhaetian especially Jurassic (Shemshak group) and the highest plant diversity of Norian in the Alborz basin is related to the phyllum of Pteridospermophytes (seed ferns) and in the Central Iran basin is related to the phyllum of Pteridophyta (ferns) indicating the higher humidity of the mentioned time in Central Iran basin and the drier climate in Alborz basin. The highest diversity of vegetation in Norian sediments throughout Iran belongs to the seed ferns (Pteridospermophyta) and the lowest diversity belongs to Ginkgophytes so that they comprise 32% (one third of the vegetation) and 6. 5% of the total vegetation, respectively. Plant-covered areas throughout Alborz were interconnected during the Norian period and there was no extensive separation between them. The plant macrofossils assemblage in both Alborz and Central Iran basins confirms the relatively humid subtropical to tropical climate for the Norian but less humidity compared to the Rhaetian. Also, the vegetation of Norian in Alborz was less dense and scattered than Central Iran during Norian.

In this research we tried to investigate the respond of high part of Zagros Mountains to past climate change by studying a 300cm core was extracted from Lake Gahar. This region is as an important biome of oak forest of Iran. Then the aim of this investigation is to detect past climate condition by palynology and climate modeling.According to the pollen diagram of Lake Gahar, four main local pollen assemblage zones during Holocene consisting of two older zones GHA (depth of 300 to 290 cm), GHB (290 to 110 cm depth) and two more new zones GHC (depth 110 to 50 cm) and GHD (depth 50 to 0 cm) were identified.We also reconstructed the annual mean precipitation and temperature data over 40000 years by MCM (Macrophysical Climate Model).The results showed that two zones GHA and GHB beyond depth 300-110cm indicate vegetation of forest- steppe with dominant species of oak trees however Quercus pollen is evident in all zones. It seems that the abrupt decreasing of arboreal pollen, especially Quercus at a depth of 50 and 60 cm at the boundary between the two zones GHC and GHD is associated with unfavorable conditions for plant growth during this period. There are also upland herbs pollen types such as Poaceae crealia types and polygonium can be considered as evidence of the destruction of the region as a result of anthropogenic effects and heavy grazing and farming operations. It is also approved the existence of consecutive period of cold/wet and warm/dry period in the past climate of Gahar region by comparing the results of this study with results from other lakes in the northwest of Iran.

The present study provides a detailed facies description and interpretation of five alluvial fans of the Qazvin Plain. In addition to tectonic activities, which lead to the localization of the alluvial fans on the northern margin of the Qazvin Plain, climate also plays a significant role in the occurrence of facies in these fans. The alluvial fans are divided into three facies groups: group 1 (alluvial fan 1), group 2 (alluvial fans 2, 4, and 5), and group 3 (alluvial fan 3). Alluvial fan 1 is dominated by the episodic matrix to clast-supported gravel (interbedded with a subordinate) and red matrix-supported gravel deposited by non-cohesive debris flow. Groups 2 and 3 are characterized by deposits of non-cohesive debris flow, mud-rich debris flows, channelized, non-cohesive debris flows, hyperconcentrated flows, and sheetfloods. The characteristics of alluvial fan 3 include highly disorganized deposits, very poorly sorted gravel, lack of erosional bases, and a wide particle-size range from clay to outsized-boulders. The facies is best interpreted as a result of debris flow following episodic localized tectonic activities of the Kavendaj Fault along with the fan head during the Quaternary Period. Relatively insignificant changes in the sedimentary facies of the studied fans from debris flows to sheetfloods during the accumulation of the three groups are attributed to a slight variation of climatic conditions, source rocks, and tectonic activities. Therefore, the debris flow-dominated fans of the Qazvin Plain recorded an arid to semi-arid PALEOCLIMATE characterized by the generation of non-cohesive debris flow and calcrete in the fans.

In this study, rainfall, percolation and hydrogeological processes relationship were evaluated using geochemical tracers to determinate PALEOCLIMATE in the Ardabil Plain. The occurrence of dry and wet periods was also determined with the help of tracer used in six profiles. The Dry and wet periods were then evaluated by the Edmund-Allison equations based on interpretation of soil water chloride concentrations and long– term precipitation measured in different periods. Applying the chloride mass balance technique to soil water chloride profiles improved the boundary conditions associated with wetter and drier climate in last times. The estimated ages through sediment cores chemistry varied from 737 years in Imijah core to 4511 years in Gharahlar core with two recorded dry and wet periods. Precipitation of recently drier climate was estimated around 202 mm in 116 last years and second drier climate was estimated around 83 mm in 473 last years. Precipitation of recently wetter climate was also estimated around 451 mm in 210 last years and second wetter climate was estimated around 703 mm in 735 last years. The second wetter had the highest amount of precipitation in 3600 years period. The Ardabil plain had a moderate drier climate since 1100 to 2900 years ago. In addition, the results showed that the wetter climate happened during last 2900 to 3550 years. According to this results, the present climate moves towards drier climate. A comparative analysis of data from six profile sites indicated that there were short term oscillations of wetter and drier climate.

Introduction Very few palynological studies have been conducted on the Nayband Formation, as a part of the Upper Triassic coal deposits of central Iran. Mousavi, 2002 (seen in Aghanabati 2004, pp. 209-210) considered the abundance and diversity of marine palynomorphs compared to terrestrial types indicate the shallow sea environment for Nayband Formation. Cirilli et al., 2005 attributed the Nayband Formation palynofloras to tropical plants such as Bennettitales, Matoniaceae, and Marattiaceae accompanied by characteristic forms of the Siberian Province. Sabbaghiyan et al., 2015 examined the palynology of the Nayband Formation, Tabas Block. They believed the associated marine palynomorphs (dinocysts), accompanied by spores indicate a nearshore depositional environment for the Late Triassic deposits. Sajjadi et al., 2015 studied the palynology of the Nayband Formation, Kamar Macheh Kuh, southeastern Tabas. They concluded that the abundance of ferns and Coniferophytes in parent flora implies that the host strata accumulated under a moist warm climate with progressively decreasing temperatures during Late Triassic. Sabbaghiyan et al., 2020 investigated the palynology of the Upper Triassic Bidestan and Howz-e-Sheikh members in Tabas Block. They believed that co-occurrence of marine elements (dinoflagellate cysts, bivalves, corals, and gastropods) with terrestrial elements (spores and pollen) shows a shallow marine depositional environment for the Nayband Formation. Materials and methods A total of 62 samples were collected from the Nayband Formation (Qadir Member), at exploratory well no. 948b. All samples were prepared following standard palynological processing procedures (Phipps & Playford, 1984), including HCl (10-50%) and HF (40%) utilized for the 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 a transmitted light microscope. Results and Discussion To reconstruct the PALEOCLIMATE of the Nayband Formation (Qadir Member) in the south of Tabas, 62 samples were collected from exploration well no. 948b for palynological investigations. The assemblage of diverse palynomorphs includes spores and pollen of land plants, dinoflagellate cysts, foraminiferal test linings, acritarchs, and algal spores with moderate to good preservation. The parent plants of existing miospores show that the diversity and abundance of ferns is 64%, cycadophytes 16%, lycophyta 9%, conifers 4%, gynophytes 4%, pteridospermophyta 2% and Bryophyta 1%. The maximum diversity and relative abundance belong to miospores attributed to ferns (64%), which indicates the predominance of warm to semi-warm climate with high humidity at that time of deposition. Based on the model of Sporomorph EcoGroups, miospores typifying all six plant communities are present in the studied strata, but the highest frequency is related to the lowlands SEGs. To reconstruct the PALEOCLIMATE variation, the large quantity percentage of four main plant groups (Hydrophilic, xerophilic, Thermophilic, Psychrophilic) was calculated and the PALEOCLIMATE study was determined by the pattern of relative abundance of drier/wetter and warmer/cooler elements. The consequences of these calculations approve the warm to semi-warm climate with high humidity conditions. Also, the paleogeographic position of Iran during the Late Triassic in the southern active margin of Eurasia (Turan Plate) is another confirmation of this type of climate. Conclusion Diverse palynomorphs with high abundance including spores, pollen, dinoflagellate cysts, foraminiferal test linings, acritarchs, and algal spores with moderate to good preservation are present in the studied material. Inferred natural relationships of the Nayband sporae dispersae imply derivation from a diverse parental flora such as ferns, Conifers, Lycophyta, Cycadophytes, Gynophytes, Pteridospermophyta, and Bryophyte. Ferns have relative abundance and maximum diversity in the composition of the vegetation around the sedimentary environment. It implies that the host strata accumulated under moist warm to semi-warm climates. In addition to, the high ratio of warmer/cooler, wetter/drier palynomorphs and the palaeogeographic position of Iran during the Late Triassic in the southern active margin of Eurasia (Turan Plate) and the location of Iran at a latitude of about 35°N, all confirm the above results that hot and humid climate prevails.

The Gurpi Formation was studied from different aspects at two sections, Farhadabad and Kavar, in southwest and southeast of flam where it is composed of 205m and 158m of grey to blue marl and shale beds and occasionally thin beds of argillaceous limestones with two formal members of Seymareh (Lopha) and Emam-Hassan. In order to reconstruct PALEOCLIMATE during depositional course of the formation, paleontological and palynological data (ratio of specialist to generalist foraminifera (e.s/e.g) and warm-temperate waters dinocysts and spore and pollen grains) were used statistically. The results show that the Gurpi Formation is mainly deposited in a warm-humid climate with two sharp decreases happening in temperature in early Maastrichtian and Danian.

1- IntroductionLake basins have spatially and temporally index patterns and represent valuable maps of physical and chemical history. According to this point, that direct survey of climate changes has only been available as machinery in the past few decades, so paleo climatic changes indexes can give a better understanding of climate changes in the past era and its causes. Lake sediments have an extraordinary potantial to record climatic and environmental events with high sensitivity and resolution amounts. Therefore, lake sediments can be considered as regions for detecting paleo environments. Chegarman Lake formed in the northeast of Khuzestan province on the hillsides of folded Zagros and under the Izeh unit in a pit. This study has been tried to by Sedimentary geochemistry analyze, Elemental ratios, identification of sedimentary facies, and identification of sedimentary environments and changes of these environments set to the reformation the climatic and environmental conditions of Chegarman wetland in the Late Holocene.2- Methods and FindingsThe steps of this research include book studies, field works, laboratory works, statistical data processing and then interpretation and conclusion. To investigate the PALEOCLIMATE and conditions of the sedimentary environment, one intact sediment cores with a maximum depth of 7.2 m collected with using Auger corer. 21sediment samples were selected for elemental analysis with ICP-OES and XRF (X-Ray fluorescence). Statistical parameters, histogram diagrams of element frequency and cluster analysis were performed to determine the relationships between the elements in SPSS software. In this study, elemental ratios of V/Cr, Mn/Al, K/Al, Rb/Al, Si/Fe, Ti/K were used to reconstruction of the paleo climatic and environmental conditions. Which led to the study of the amount of detrital material, the severity of weathering and erosion in the catchment and fluctuations in the water level of the lake.3- Results and discussionIn the studied core, 5 major sedimentary facies identified. Facies often contains clay, silt, gravel, and interstitial sediments along with vegetation and shell fossils which in most cases frequency and interference in the mentioned sediments are often seen. Changes were in particle size between clay to gravel due to process type changes, environment's energy and river input's amounts and sediment color variations concerning sedimentation conditions, presence of organic matter, pH amount, salinity and temperature variations, and drought occurrence, throughout the cores. Two wetland sedimentary and alluvial environments identified. According to the Chronology, the average sedimentation rate in the Chegarman wetland is 1.4 mm / year, which this amount is different for various depths (Darvishi et al., 2022). Due to the type of sediments, the high level water period of the Chegarman wetland has been established between 1250 and 150 years ago. The study of the facies sediments of the wetland bed shows that climate change occurred gradually (not suddenly) about 1250 years ago and this trend has taken at least 300 years. The relatively dry and cold period lasted about 1850 years from 3100 years to 1250 years ago and is confirmed with the reported dry periods in the Maharlou Lake about 1800 years ago, in the Mir Abad Lake about 1500 years ago and in the Urmia Lake between 2500 and 1500 years ago. From 4000 years ago to about 3100 years ago, stable and slow wetland conditions was prevailed. The conditions for creating a peatland environment have been provided in the wetland and were associated with increasing the amount of organic matter, vegetation and shell fossils and consequently increasing sedimentation rate. This period which lasted for about 900 years, has been accompanied by extremely humid conditions, high groundwater level and activity of springs in the region. The existence of light brown mud which has the age ranges from 4900 to 4000 years ago, indicates a dry period (900 years). This dry period shows suitable approximate conformity with a dry event of 4200 years ago in the northern hemisphere. This period in the studied region appeared with at least 100 years of temporal delay. After this dry period, we see again a gray sequence with plant and shell fossils that continue to a depth of 7 meters (about 5000 years ago). At depths of 7 to 7.2 m, the existence of brown-muddy sediments along with coarse-grained sediment in size of gravel, pebble and rubble, strengthen the possibility of very strong flood in the region that sent the coarse-grained sediments of around formation to bed of the wetland or maybe has hit to the area of wetland sediments bed in the region.4. Conclusion According to the results of surveys in the Chegarman wetland, at least 2 high water periods with humid climate and at least 2 dry periods during the Late Holocene were identified. Dry periods appear more suddenly and with more intensity and shorter duration than humid periods in the region and gradually lead to from very dry periods to semi-arid, semi-humid, and eventually humid periods.