Clay mineralogy and evolution of soils in a catena in Behshahr area, Mazandaran Province

Clay mineralogy and evolution of soils in a catena in Behshahr area, Mazandaran Province Catena is defined as the range of continuous soil series which are at a toposequence and also called drainage sequence. The main objectives of this research were: 1. to study the combined effects of topography and drainage conditions and water table depth on formation and evolution of soils, and 2. To investigate the hydromorphic and halohydromorphic soils of Miankaleh lowland area as wildlife habitat and tourist attractions. The study area is in the south-eastern Caspian Sea with a temperate climate, xeric soil moisture regime and thermic soil temperature regime. Three geomorphic surfaces determined in the area are consisted of hillslopes, alluvial plains and lowlands. Five representative pedons were investigated using present soil maps of the area along North-South transect. The low lying soils near sea were classified as Aquisalids and Halaquepts, and gleization has occurred. Based on field observations and previous studies it appears that this region has come out of the water during the past century. In the alluvial plain in agricultural lands, Haplaquolls and Haploxerepts were dominant with high organic matter accumulation. In Haplaquolls accumulation of clay and gleization were observed. In Haploxerepts, vertic properties were dominant. Finally in hillslopes of the north-facing slope of Alborz under forest vegetation Haploxeralfs were formed with argillic horizon and decalcification has occurred. The clay mineralogical results showed that illite was dominant clay mineral in low lying and alluvial plain soils, but in hillslope under forest vegetation smectite is dominant mineral. Vermiculite is also found in the soil of hillslopes well. Due to lack ofthe necessary conditionsfor the formation ofkaolinite, this mineral is inherited from the parent material. The presence ofillite and chlorite minerals in area soils have a hereditary origin. In hillslopes due to greater leaching and forest cover, weathering more done and make more smectite and vermiculite is formed. Intensivedecrease of chloritein the pedon in the forest, because weathering more is rational. In this pedon, The percentage of smectiteclaymineralin thesubsurfacehorizonis significantlyhigher thanthe soillevel. In alluvial plain soil the amount ofillitereducedandsmectitethere isa considerable amount that could beresult of smectite formation from the weathering of illite.In low lying soils due to aquic condition, condition provided for smectite authigenesis, and smectite in these soils are also found to be significant.As a result, smectitehastwo pedogenicsources(soil solution) andillite and chloritemineralsismodified