Paleopedological study of loess-paleosol sequences along a climosequence in northern Iran

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.