فهرست مطالب martin kehl

During the Quaternary period mid to high-latitude areas were affected by loess deposition. In Iran's northern and northeastern regions, significant loess deposits are prevalent and distributed throughout the Iranian Loess Plateau and along the northern foothills of the Alborz Mountains. Intercalated within these loess deposits are paleosols, formed during warm and moist climatic conditions (interglacial period). These paleosols offer an opportunity to study the climatic and environmental changes that occurred during the Quaternary period. Understanding the relationship between loess deposition and paleosol formation can offer significant insights into the mechanisms that drive changes in global climate and how they affect the Earth's geology and ecosystems. Studies have shown that loess sediments and loess-derived soils contain different concentrations of iron minerals such as hematite, iron oxyhydroxide, and goethite. These minerals are highly sensitive to environmental changes, and evaluating the changes of these minerals in loess-paleosol sequences can be a valuable indicator for studying paleoenvironmental changes. The two main minerals that cause color and magnetic susceptibility changes in loess-paleosol sequences are goethite and hematite. Therefore, the assessment of loess-paleosol sequences from the aspect of magnetic and colorimetric parameters provides the possibility to identify paleoenvironmental and climatic changes. The main goal of this research is to investigate the changes in iron oxides in the loess-paleosol sequence in the east of Golestan province using colorimetric techniques and temperature-dependent magnetic susceptibility in order to provide enough information for reconstructing the paleoclimatic conditions during the formation of paleosols.

Sampling was performed from the loess-paleosol sequence in the eastern Golestan province, for each loess and paleosol horizon. Initial colorimetric and magnetic susceptibility measurements were carried out respectively for 1345 and 24 samples at LIAG Institute in Germany. Color measurements were carried out with a spectrophotometer machine that covered the visible light range. The temperature magnetic susceptibility was carried out using in the 20–700°Ctemperature range in an argon atmosphere to minimize oxidation.

According to the results of this study, we can mention the identification of iron minerals in loess and paleosol samples using colorimetric analysis. Iron minerals such as hematite, goethite, and maghemite can be detected at wavelengths 565, 435, and 595 nm, respectively. Colorimetric results showed that the ratio of hematite to goethite of paleosols has increased compared to loess sediments in the study area, which indicates the increase in precipetation and soil moisture during the interglacial period. The heating curve (temperature-dependent magnetic susceptibility) of loess samples at 560-590 degrees Celsius showed a sharp decrease due to magnetite minerals in these samples. At the same time, this happens in paleosols at a temperature of 300-350 degrees Celsius, which is due to the loss of the maghemite mineral formed during the interglacial period. The results showed that the decrease in the heating curve in paleosols indicates the increase in the intensity of soil-forming processes.

The results of this study showed that iron minerals such as magnetite, maghemite, hematite, and goethite in loess and paleosols play an important role in magnetic properties and soil color. Also, the increase in the presence of hematite and maghemite in paleosols indicates the increase in the intensity of soil formation processes and humidity during the formation of paleosols. The results of this research showed that the colorimetric technique, along with temperature-dependent magnetic susceptibility, can be one of the fast and accurate methods in studying and identifying paleosols.

The study of loess sediments and loess-derived soils, which cover approximately 10% of the Earth's surface, is of considerable importance because of their potential to provide information on the paleoenvironment, particularly during the Quaternary. The northeastern region of Iran, with its unique climatic archive, is of significant importance as a repository of Quaternary period deposits, attracting much attention from Iranian and international scientists in recent decades. Considering that soil forms in response to interactions among the lithosphere, hydrosphere, and atmosphere, it potentially contains physical, biological, and chemical environmental information at the time of its formation. The process of becoming loess sediments into paleosol depends on various factors such as vegetation, weather, topography, microbial activity, and time, so paleosols have the potential to restore the paleoenvironment by maintaining the effect of these factors. Therefore, studying soils derived from loess can enhance our knowledge and understanding of past climatic conditions in the region and the world. Studying undistributed soils using microscopic techniques can provide valuable information for understanding the environmental and climatic conditions during the formation of derived soils from loess (paleosols). One of the quantitative methods for studying micromorphology samples is the use of indices such as MISECA, which indicate the degree of paleosol evolution. By using this index, we can have an approximate estimation of paleoprecipetation. The main aim of this research is to reconstruct the precipitation amount during the formation of late Pleistocene paleosols in the eastern part of Golestan province, using micromorphological studies.

In order to conduct this research, after field visits, a profile of approximately 55 meters was excavated to examine the identified loess-palaeosol sequences. Then, undisturbed samples were obtained from each horizon to prepare thin sections, and the samples were impregnated under vacuum conditions using a combination of resin, acetone, and catalyst. After the samples hardened, a thin section was cut from them and affixed to a glass slide. The thin sections were then polished using sandpaper until a thickness of 30 microns was achieved. The prepared thin sections were studied using a polarizing microscope.

Micromorphological analysis of the samples revealed that the presence of horizons rich in calcium carbonate and clay in well-developed paleosols has a significant relationship with increased precipitation.  Micromorphological studies showed that the coarse to fine (C/F) relative distributed results showed that the amount of it in loess horizons and weakly developed paleosols are 4/6 or 3/7 but this ratio in moderately and well-developed paleosols become smaller in comparison with loess horizons, indicating the weathering and leaching of primary minerals in loess sediments and their transformation into secondary minerals in paleosols. Furthermore, with increasing paleosol evolution, the microstructure of the samples changed from massive to subangular blocky and then to angular blocky. Therefore, the results of examined microstructure in the samples showed that it can be one of the important factors for identifying paleosols from loess horizons and paleoenvironment conditions. Based on the data obtained from the MISECA index, the degree of paleosol development ranged from weakly developed (MISECA index was smaller than 8) to well developed (MISECA index was bigger than 16). The estimated paleoprecipitation amount using this index showed that paleosols with weak development formed under climatic conditions with precipitation less than 500 mm per year, while paleosols with moderate and well developed formed under climatic conditions with average precipitation of 500 to 800 mm per year and more than 800 mm per year, respectively.

Considering that soils are formed as a result of interactions between the lithosphere, hydrosphere, and atmosphere, they potentially contain physical, biological, and chemical information about past environmental conditions. Therefore, by studying the Late Pleistocene loess-paleosol sequences in Golestan province, it is possible to reconstruct past climatic changes in northeastern Iran. The micromorphological investigation of the loess-paleosol sequence under study showed that the processes of transfer and deposition of clay and secondary calcium carbonate and the subsequent creation of horizons rich in clay and secondary calcium carbonate are among the most important pedogenic processes in well-developed soils. Micromorphology can be a useful tool for investigating the paleoclimate and paleoenvironments conditions during the formation time of paleosols. The results showed that the use of the MISECA index can be a valid and logical method for evaluating the degree of paleosol development.

Biological soil crusts are a community of cyanobacteria, fungi, lichens, and mosses and play key roles in arid and semi-arid regions including carbon and nitrogen accumulation, soil fertility, dust capture, soil conservation and stability. Recent studies show that the formation of biological soil crusts on mobile dunes areas is extremely difficult due to low vegetation cover, strong sand flow activity, and soil surface instability. If sand activity is controlled by the wind and the soil surface is stabilized by cover establishment and/or mechanical factors, the biological and physical crusts gradually form on the soil surface. These soil crusts play an important role in establishment and evolution of sand dunes. Lichen biological soil crusts and physical crusts are widespread on early Holocene sand dunes in the north of Golestan province. The aim of this study was to investigate the effect of lichen biological soil crusts on surface soil properties and consequently evolution and stability of sand dunes.

Sand dunes around the Alagol wetland located in the north of Golestan province were selected for this study. Lichen biological soil crusts species were collected after extensive filed study and transferred to the laboratory for identification. Three lichen species including Diploschistes diacapsis (Ach.) Lumbsch, Gyalolechia fulgens (Sw.) Søchting, Frödén & ArupFulgensia fulgens (Sw.) and Squamarina lentigera (Weber) were identified. After identification, soil samples were taken from two depths beneath lichen biological soil crusts and physical crusts. Then, soil samples were transferred to laboratory and some of physical, chemical and biological soil properties including total organic carbon, carbohydrate, calcium sulfate, equivalent calcium carbonate, mean aggregate diameter, particle size, pH and electrical conductivity were measured using standard methods. In addition, soil samples were taken from two meter depths (parent material) for particle size analysis. In this research, a completely randomized factorial design with three replications was used to analyze the data. The means were compared using LSD method at p < 0.05. SAS software was utilized to analyze the data, and the figures were drawn using Excel software and GRADISTAT (Version 8.0).

The results showed that presence of lichen biological soil crusts and physical crust changes the surface soil properties. Soils derived from aeolian deposits beneath of various lichen biological soil crusts had higher total organic carbon, carbohydrate and mean aggregate diameter in comparison with physical crusts. D. diacapsis and S. lentigera species had improved physical, chemical and biological soil properties compared to G. fulgens species. The effect of biological soil crusts on soil properties decreased with increasing soil depth. There was a high correlation between mean aggregate diameter with total organic carbon and carbohydrate. Electrical conductivity strongly decreased in soils cover with D. diacapsis and S. lentigera species compared to physical crusts and G. fulgens species in two depths. Calcium sulfate was higher in soil covered by G. fulgens in comparison with D. diacapsis and S. lentigera species. The content of fine sand and coarse silt in soils covered by lichen biological soil crusts was higher than physical crusts. Whereas, the content of fine silt and clay content covered by physical crusts were higher or similar to lichen biological soil crusts. Parent material had greater particle size distribution in comparison with surface soils covered with biological soil crusts and physical crusts. These results show that soil crusts are formed in soils with finer particle size. Biological soil crusts can increase fine particle content with two mechanisms including capture dust and weathering soils. The secretion of extracellular polysaccharides (carbohydrate) and rough surface morphology of biological soil crusts may help to capture dust (fine sand and coarse silt). Soil pH and calcium carbonate were lower in soils covered with lichen biological soil crusts compared to physical crusts.

The presence of biological crusts on soils derived from early Holocene aeolian deposits apparently plays an important role in improving soil properties. Well-developed lichen biological soil crusts including D. diacapsis and S. lentigera species may significantly lead to establishment and stability of soils derived from early Holocene aeolian deposits. It seems that G. fulgens species grow better on coarse-grained soils with higher calcium sulfate content. Lichen biological crusts increase the mean aggregate diameter and consequently increase the stability of the soil surface.  Lichen biological soil crusts have an important role in dust capture and resulted in increased fertility of soils derived from early Holocene aeolian deposits.

 One of the processes of the Quaternary era is the glacial and interglacial periods. In the glacial period, loesses deposited and in the interglacial period, Paleosoils were formed. The northern part of Iran is geographically the same as countries such as China, a large part of which has been covered with loess sediments during the Pleistocene glacial period. Loess sediments in northern Iran reflect several cycles of climate changes and the evolution of the earthchr('39')s appearance for the middle to late Quaternary period. In this region, the Loes-Paleosoil sequences are one of the most important terrestrial archives of climate change and provide a bridge between Southeast European and Central Asian loess sediments. To reconstruct paleoclimate changes, magnetic susceptibility is used as a climate proxy. The high magnitude of the magnetic susceptibility indicates the large volume of magnetic minerals. Chemical weathering causes the formation of magnetic minerals such as magnetite and maghemitite. These minerals are abundant in Paleosoils and can be determined by analyzing the magnetic susceptibility of Loess and Paleosoils. The magnetic properties of the Loess-Paleosoil sequence are considered to be evidence of paleo precipitation and weathering.Study area Geographical location of Saadabad sedimentary section in the northern region is 36° 49chr('39') N and 54° 22chr('39') E, at an altitude of 140 m a.s.l. Saadabad sedimentary section is located in the construction zone of Alborz and in terms of the main sedimentary-structural zones of Iran is part of the southern Caspian coast. This zone includes areas, which are located in the north of Alborz fault and block the Caspian Sea coast on the coast of Iran and are covered to the east with thick layers of loess.

In the field work that was carried out in May 2017, after determining the exact location of the sedimentary section, sampling was performed. Before sampling, aerated sedimentary layers are dug up and removed to reveal fresh deposits. Then, using the meter, the layers were divided into 10 cm intervals. 92 samples were prepared at 10 cm intervals from the sequence. Measurement of natural residue magnetic (NRM), by the model rotating magnetometer (JR-6A), and measurement of magnetic susceptibility by magnetic intensity measuring device, in the magnetometry laboratory of the Geological Survey of Iran.

Table 1 shows the measured values of the magnetic parameters. Due to the length of the table, only a few examples are given in the table. Since high magnetic susceptibility can indicate a greater concentration of magnetic minerals in the sample, it can be concluded that the paleosils of the sequence studied have more magnetic materials than the loesses, which are inside the soils. They can be the result of podogenesis processes. Because rising temperatures and humidity cause soil erosion processes and increase oxidation and thus increase the amount of magnetic materials, it can be concluded that in paleosoils with higher magnetic susceptibility, warm and humid climates dominate in the environment. Micromorphological studies of directional clay layers, Fe-Mn hydroxide, show that the palaeosoil of section 5 is moderate to well developed. As the climate changes to higher temperatures and higher humidity, weathering and pedogenesis also increase, leading to the development of a pedogenic oxidation environment as a result this produce the formation of tiny magnetic grains such as maghemite and magnetite in this oxidizer environment and thus increases the magnetic susceptibility. In Saadabad, the high amount of xlf along with the high percentage of xfd suggests that many of the ultra-fine maghemite and magentite grains may have been formed during pedogenesis under a long, humid, warm climate. The findings show that the different behaviors of magnetic susceptibility between the loess of the drier and wetter areas are mainly caused by their different pathogenic environments, which in turn are related to local topography and climatic conditions.

High levels of xlf and xfd indicate high precipitation during the formation of Paleosoils. Post-sedimentation processes may increase the amount of MS by producing new ferromagnetic minerals during the oxidation of wheathered soils, and may also reduce the amount of MS by reducing the processes. The clay material in which the soil is made is the main factor influencing the change in magnetic mineralogy and magnetic susceptibility. This study also shows that magnetic susceptibility is a complex parameter and its use as a precipitation control has certain limitations and conditions, and when the magnetic properties of the loesses are used for paleo climate reconstruction, more attention should be paid to topography, environment. Sediment and weather factors.

Introduction The loess-paleosol sequences in Northern Iran are important archives that represent several cycles of Quaternary climate change and can be used to complete the information gap on loess between Europe and central Asia. Last interglacial soils derived from loess in northern Iran is represented by strongly developed Bt horizons of forest soils. In Golestan and Mazandaran area, soils under the forest are mainly classified as Alfisols or Luvisols. Interestingly, E horizons are generally not found in these soils. In the Caspian Lowlands, a pronounced precipitation gradient is reflected in mean annual precipitation rates decreasing from about 1850 mm at Bandar Anzali in the west to about 435 mm at Gonbad- e Kavoos in the east. The results of the loess climosequence in Northern Iran showed that with increasing precipitation, soil pH and calcium carbonate contents decrease, whereas soil organic carbon, clay content, and cation exchange capacity increase. For years, many efforts to quantify the soil properties led to the provision of indices of soil development. Among these indices are forms and ratios of iron, morphological, and micromorphological indices. Many studies have been carried out on the loess-paleosol sequences and modern loess soils in Northern Iran with focus on micromorphology, mineralogy, and dating but more investigation is needed with an emphasis on the forest soils with well-pronounced clay illuviation as a proxy for paleo-moisture. For this purpose, we used micromorphology and soil color indices to report the effects of precipitation gradient on the variability in the formation of soils under forest vegetation. Materials and Methods The study area is located at the northern slopes of Alborz Mountain Ranges, covered with Caspian or Hyrcanian deciduous forests. Field sampling started in summer 2015. More than ten soil pedons with loess parent material were investigated based on former studies. Finally, six representative modern pedons were selected and dug in an east-west direction on loess deposits. The climate data shows that precipitation varies from 500 mm in Qapan (Pedon 1) to up to 800 mm in Neka. Physiochemical properties of soils were studied using standard methods. Thin section prepared for soil micromorphological studies were studied and interpreted based on Bullock et al. and Stoops guideline using a polarizing microscope. The micromorphological index of soil development (MISECA), suggested by Khormali et al (2003), was calculated. Also, color indices were calculated based on Hurst (1977), Torrent (1983), and Alexander (1985) by using the Munsell color chart. In all color indices, Munsell color hue converts to a single number. Results and Discussion The results showed that the downward decalcification and the subsequent clay illuviation were the main criteria influencing the assessment of soil development in this study. So, all of the soils host argillic and calcic horizons and are classified as Alfisols and Mollisols. Micromorphological studies confirmed the morphology studies in the field and the results of physico-chemical analyses. MISECA index showed pedological changes in different pedons in the studied areas. A significant positive relationship between climate gradient (increasing rainfall) and MISECA index was found. The area and thickness of clay coatings show an increasing trend with rainfall. Occurrence and preservation of clay coatings are more pronounced in more humid regions with illite and vermiculite as the dominant clay minerals. These minerals reduce the shrink/swell potential and increase the number of clay coatings present. In Argillic horizons of all pedons, except Toshan, dominant b-fabric is speckled due to carbonate leaching, while in Toshan, it is striated b-fabric. In calcite horizon, b-fabric is crystallitic. The correlation of various forms of iron with three color indices of Hurst, Torrent, and Alexander showed that Torrent and Alexander indices were better than the other one for the study area. Moreover, there was a good correlation between MISECA and Torrent color index. Conclusion The results showed that the soil evolution in the studied areas is strongly influenced by soil formation factors, especially in a climate which shows a change in the micromorphological characteristics of soils. With increasing the rainfall from the east to the west in this gradient, the amount and thickness of clay coating, as well as secondary calcium carbonate accumulation, change significantly. In addition, the micromorphological and color indices of soil evolution can be used as two indicators for assessing the effects of rainfall gradient on soil formation in northern Iran. On the other hand, knowledge of the development of modern loess-derived soils could help to better understand the paleoenvironment.

Loess deposits on the slopes of Alborz mountain in northern Iran represent the most important geoarchive of climate change in the region and provide an important link between loess deposits in Southeastern Europe and Central Asia. These deposits are so important because of preserving palaeosols to reconstruction of past soil formation processes and consequently, climate condition on formation time. Therefore, this study for palaeopedological investigation on three loess-palaeosol sequences (Agh Band, Mobarak Abad and Neka) to reconstruction of past pedogenesis processes was done along a climosequence in northern Iran. Three loess-palaeosol sequences including Agh Band, Mobarak Abad and Neka sections were studied in Golestan and Mazandaran provinces in northern Iran. Agh Band section is located in the westernmost part of the Northern Iranian loess plateau. The section at Mobarak Abad is exposed in a deep road cut located on the northernmost ridge of the Alborz Mountains. Neka loess-palaeosol sequence located on the top of a deep Iimestone quarry about 10 km east of Neka. Soils sampling was done in several field campaigns in spring 2012. After soil sampling and field description, some physic-chemical properties was analyzed. Six modern soil profiles (for comparison) were dug along this climosequence which classified as Entisols, Inceptisols, Mollisols and Alfisols. Results of physico-chemical analyses show silt particles were dominant particle (more than 50 percent) in the loess-palaeosol sequences and modern soils which confirmed aeolian source of loess deposit. Clay content increased from Agh Band to Mobarak Abad and Neka section while silt content decrease which it may reflected weathering processes of clay and/or it’s translocation and the distance from loess source. Carbonates amount were variant in different horizon (about 15-20 percent) which reflected climate condition and pedogenesis activity. Results shows one preliminary soil formation stage in Agh Band section whereas Mobarak Abad shows about 5 periods and Neka at least 4-6 periods in different pedogenesis levels and soil develop degrees. Soil development and variation in soil horizons increase (in both palaeosols and modern soils) along of climosequence (from dry to moist region) that reflected pedogenic activity which has direct relation with climate. These results show the modern climate gradient (especially for precipitation) existed during the time and climate change control amount and intensity of soil formation processes.