clay mineralogy of soils on quaternary sediment in northeast of urmia

introduction: minerals are one of the main components of soils which play different roles in the soils. minerals make up about 50% of the volume of most soils. they provide physical support for plants, and create the water- and air-filled pores that make plant growth possible. mineral weathering releases plant nutrients which are retained by other minerals through adsorption, cation exchange, and precipitation. minerals are indicators of the amount of weathering that has taken place, and the presence or absence of particular minerals gives clues to how soils have been formed. the physical and chemical characteristics of soil minerals are important consideration in planning, constructing, and maintaining of buildings, roads, and airports. clay minerals can be used for understanding of soil formation, optimum management of dry and wet lands and interpretation of paleo environments. moreover, clay minerals can provide some valuable information such as the origin of sediments, transportation and precipitation of sediments and also some information about intercontinental weathering regimes. quaternary sediments have occupied most of the agricultural and natural resources of urima plain and recognition of mineralogical of these soils is essential to optimum and stabile use of these soils. additionally, caly mineralogical investigation can provide some information about the intensity of weathering processes and climate change in this area. thus, in this study clay minerals of quaternary sediments in northeast of urmia and the mechanisms of their formation and also tracing probable climate change in this area were investigated. materials and methods: this study was performed in theurmia plain in west azerbaijan province. the study area is located on quaternary sediments and physiographically, this area is a part of a river alluvial plain with the gentle slope toward urmia lake. the mean annual precipitation and temperature of this area are 345.37 mm and 10.83 °c respectively and the soil moisture and temperature regimes are dry xeric and mesic respectively. in this study, eight soil profiles in quaternary sediments were dug and sampled and the morphological, physical, chemical and mineralogical properties were determined using standard methods. results and discussion: according to the results, illite, smectite, kaolinite, chlorite, vermiculite and hydroxy interlayer vermiculite (hiv) were the dominant clay minerals in these soils. the origin of illite, chlorite and kaolinite were related to inheritance from parent material. regarding to the present of some smectite in the parent material of these soils, some of smectites have been inherited from parent material. nevertheless it seems that, the most of smectites in these soils have pedogenic origin. based on mineralogical results and trends variation of smectite and illite along studied profiles, we concluded that some of smectites in these soils have been formed from illite transformation. in profiles 4 and 6, regarding to low depth water table and consequently poor drainage, high ph and high values of calcium and magnesium cations, provide suitable conditions for the neoformation of smectit and so, some of smectites have been formed via neoformation from soil solution. in these soils, vermiculites were pedogenic and have been formed during transformation of illite to smectite. small amounts of hydroxy interlayer vermiculites were present in buried horizons and regarding that they were not present in parent material, it might be because these minerals are pedogenic and have been formed in a past wetter climate. the transformation of illite to smectite in lower horizons needs high moisture and regarding to recent semiarid climate of study area, the suitable amount of moisture for this transformation, especially in lower depths and also in buried horizons, is not present. thus, it seems the transformation of illite to smectite in lower depths and buried horizons has been taken place in a wetter past climate. so we concluded that smectite and hydroxy interlayer vermiculite are evidences of a wetter past climate in this area. conclusion: in this study the origin of smectite in buried horizons was related to transformation of illite. according to high moisture condition which is necessary for the weathering of illite, the occurrence of this process related to more humid climate of the past. additionally, the presence of hydroxy interlayer vermiculites was related to previously wetter climate as well. so results of this study can be used for recognition of climatic change in the study area.