Micromorphology and Clay mineralogy
Masoumeh Pourmasoumi Parashkouh; Farhad Khormali; Shams Ollah Ayoubi; Farshad Kiani; Martin Kehl; Eva Lehndorff
Abstract
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 ...
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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.
Micromorphology and Clay mineralogy
masoomeh najafinia; Fashad Kiani; mojtaba Baranimotlagh
Abstract
Introduction Loess sediments of northern Iran represent several cycles of climate change and evolution of the landform for the mid-to-late Quaternary. Climate change in elevations of Iran and its surrounding areas is very controversial in the mid and late Quaternary, and has been discussed in the past ...
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Introduction Loess sediments of northern Iran represent several cycles of climate change and evolution of the landform for the mid-to-late Quaternary. Climate change in elevations of Iran and its surrounding areas is very controversial in the mid and late Quaternary, and has been discussed in the past according to rainfall and rainfall periods and between rainfall, glacial and inter-glacial. Paleomegnatic results also indicate that these sediments have accumulated between, 1.8 to 2.4 million years ago. However, pedogenic processes and the effects of past climate in these soils still have not been fully investigated. The loess deposits in northern Iran are a valuable archive of regional paleoclimatic and paleoenvironmental information. Extensive sedimentological and chronological studies have been carried out on the middle to upper Pleistocene loess during the past decades, but it is necessary to do a comparative research on the older loess deposits. So, this study aimed to conduct a mineralogical and physicochemical investigation on the early Pleistocene loess and to compare it with modern loess soils in Agh-Band, Yelli-Badrag and Qareh-Agach in loess plateau of eastern Golestan. Materials and Methods The study area is located in a hot and dry climate in loess Plateau east Golestan. According to the previous studies, a total of six profiles were excavated and studied. Then, physicochemical properties such as soil texture, acidity (pH), electrical conductivity (EC), saturation moisture (SP), organic carbon (OM), cationic exchange capacity (CEC) and calcium carbonate equivalent (CCE) were measured in the laboratory. Clay separation was carried out with a specific method to separate the clay as well as identification of clay minerals. After preliminary field observations and determining the horizons for each profile in the region, soil classification was done based on soil taxonomy and WRB. Then, soil samples were prepared from each horizon for physicochemical and mineralogical studies in sufficient quantities. Results and Discussion Comparing the results of physicochemical properties (such as color, lime percentage, the cation exchange capacity and the ratio of iron, etc.) in paleosol and modern loess soils indicates that in paleosol soils, soil forming processes have passed several stages. Clay mineralogy is a good indicator for past climate change studies in loess.The existence of the arglic horizons and the evolved calcic in paleosols and their absence, in comparison with the modern soils in which they are present, indicate the change in soil formation conditions. The change in the color of paleosols also represents the soil moisture and the more suitable conditions of the past climate (temperature, and especially rainfall) in comparison with the present climate of the region, this color change was due to activation of soil formation processes in paleosols. All paleosol samples had a higher clay content than the late modern loess soils of the Pleistocene, suggesting favorable climatic conditions for soil formation processes and the development of more ancient soil than parent materials. Decrease in the amount of annual precipitation in the region, compared to the past, has led to decreased smectit and increased chlorite. Therefore, presence of smectit cannot be attributed to the present situation of the region. The presence of these clay minerals in paleosols can be due to wet weather conditions as well as weathering of clay mineral deposits. On the other hand, the dominance of less weathered clay minerals such as illite and chlorite in the late Pleistocene modern loess soils is correlated with the present dry climatic conditions. Conclusion The simultaneous presence of modern and old loess soils in the studied areas demonstrates the general evolution of geographical and climatic conditions during the Pleistocene period which has altered the properties of these layers and ultimately left out the effects of high clay conditions, which is a combination of climatic evidence and intermittent pedogenic soil formation processes. The presence of early Pleistocene loess soils between late Pleistocene loess sediments in Golestan province and the conditions of the study provided pedological and mineralogical comparisons of modern and paleosols in these areas and the results clarified a part of the climate change in northern Iran. The past climate study allows for prediction of the current and future climate change process. Therefore, a more accurate study of clay minerals as the key to all soil behaviors and past climate change in different parts of the eastern Golestan plateau can be very useful in completing studies of evidence of past climate change in paleosol soils
Micromorphology and Clay mineralogy
masoomeh najafinia; Farhad Khormali; Farshad Kiani; mojtaba Baranimotlagh
Abstract
Introduction Loess sediments of northern Iran represent several cycles of climate change and evolution of the landform for the mid-to-late Quaternary. Climate change in elevations of Iran and its surrounding areas is very controversial in the mid and late Quaternary, and has been discussed in the past ...
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Introduction Loess sediments of northern Iran represent several cycles of climate change and evolution of the landform for the mid-to-late Quaternary. Climate change in elevations of Iran and its surrounding areas is very controversial in the mid and late Quaternary, and has been discussed in the past according to rainfall and rainfall periods and between rainfall, glacial and inter-glacial. Paleomegnatic results also indicate that Early Pliestocene loess (Reddish loess) have accumulated between, 1.8 to 2.4 million years ago. However, pedogenic processes and the effects of past climate in these soils still have not been fully investigated. The loess deposits in northern Iran are a valuable archive of regional paleoclimatic and paleoenvironmental information. Micromorphology is an important technique to identify and interpret the loess- paleosol for paleoclimate studies. Microscopy is a method of studying undisturbed soil samples with the help of microscopic techniques (and sometimes with ultramicroscopic ones), in order to identify their constituents, determine their mutual relations in space and time and interpret their formation conditions. Micromorphology uses these characteristics to make interpretations, generally on the soil formation processes. This study aimed to conduct a micromorphological investigation on the early Pleistocene loess and to compare it with the modern loess derived soils in Agh-Band, Yelli-Badrag and Qareh-Agach in loess plateau of eastern Golestan. Materials and Methods The study area is located in semiarid climate in loess Plateau east Golestan. Six profiles were selected and studied. Physicochemical properties such as soil texture, acidity (pH), electrical conductivity (EC), saturation moisture (SP), organic carbon (OM), cationic exchange capacity (CEC) and calcium carbonate equivalent (CCE) were measured in the laboratory. Then, soil samples were prepared from each horizon for micromorphology studies. For micromorphological studies, thin sections were prepared from undisturbed, oriented and dry clods by standard methods and described under a polarizing optical microscope. Results and Discussion Comparing the results of physicochemical properties (such as color, carbonate percentage, the cation exchange capacity, etc.) in paleosol and modern loess soils indicates that the in paleosols, soil forming processes have passed several stages. The existence of the argillic horizons and the evolved calcic in paleosols and their absence in the modern soils in which they are present, indicates the change in soil formation conditions. The change in the color of paleosols also represents the soil moisture and the more suitable conditions of the past climate (temperature, and especially rainfall) in comparison with the present climate of the region. This color change was due to activation of soil formation processes in paleosols. All paleosol samples had a higher clay content than the late modern loess soils of the Pleistocene, suggesting favorable climatic conditions for soil formation processes and the development of more ancient soil than parent materials. Reducing annual precipitation decrease soil pedogenesis. Conclusion Comparison of the results obtained from paleosols of early Pleistocene with modern soils indicates that the time and climate change caused alterations in the soil micromorphology features (such as the type and amount of pores, soil structure and b-fabric and pedofeatures etc.). One of the most important pedofeatures was clay coating around void, presented only in buried paleosols, which is the evidence for moist climate conditions and subsequently enough leaching for clay translocation. Further, the presence of planar void caused by shrink and swell of clay is evidence for evolution in the paleosols. In argillic horizons of paleosols, dominant b-fabric is speckled due to carbonate leaching while in calcite horizon, it is crystallitic b-fabric. The micromorphological index of soil development calculated, showed that these red-colored deposits are formed under an annual precipitation of about 450- 650mm which represents more humid conditions at the time of their formation than the modern loess soils. In modern soils derived from recent loess, lack of clay coating can be a reason for weakly developed soil formation.
Soil Biology, Biochemistry and Biotechnology
M. Soliemanzadeh; H. Khademi; M. Sepehri
Volume 37, Issue 2 , March 2015, , Pages 59-72
Abstract
Microorganisms play an important role in providing nutrients for plants and also in soil development. This study was carried out to investigate the effect of two strains of Bacillus cereus on the release of potassium and iron from micaceous minerals. An experiment was set up with a completely randomized ...
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Microorganisms play an important role in providing nutrients for plants and also in soil development. This study was carried out to investigate the effect of two strains of Bacillus cereus on the release of potassium and iron from micaceous minerals. An experiment was set up with a completely randomized design and factorial arrangement with three replications. Treatments included two types of mineral (phlogopite and muscovite), two strains of bacteria (PTCC 1247 and PTCC 1665), control and eight time periods. The results indicated that released potassium and iron were highly dependent on the strain of bacterium and also the mineral type. Strain PTCC 1665 could release a higher amount of potassium as compared to PTCC 1247. The amount of released iron increased at the beginning of the experiment but decreased and then increased as time passed. In general, the amount of released iron from phlogopite was higher than that from muscovite.
