Khormali, F.–Kehl M.–Frechen M.: Loess-Paleosols and Modern soils of Northern Iran, Paleoclimatic implications
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szeptember 24.
2021
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Horváth Erzsébet
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The extensive loess deposits of Northern Iran occur in the two different loess provinces of the Alborz Mountain footslopes and the so-called Iranian Loess Plateau and reach a thickness of about 70 m. A pronounced precipitation gradient of about 800 mm year-1 over 80 km from north to south and corresponding vegetation from dry steppe over steppe grassland to forest vegetation provides condition for the formation of a variety of modern soils on loess and will have governed soil formation during the past as well.
In this study we discuss the major properties of modern and fossil soils and suggest pedostratigraphic correlation of loess-paleosol sequences developed along assumed precipitation gradients of the past. Eight representative pedons were selected in a south-north direction on loess deposits. The climate data show that precipitation varies from 200mm in the upper north regions to up to 900mm in the southern areas of Alborz north facing slopes in less than 80 km latitudinal distance. Three loess-paleosol sections were also investigated on the south – north gradient. Sedimentological and pedological properties were investigated to characterize the development degree of soils and use them for correlation of loess-paleosol sequences at Neka, Toshan, Now Deh and Agh Band.
In the northern arid regions, Aridisols with gypsum and carbonate accumulations are formed. Organic matter accumulation and the formation of mollic epipedon are the dominant processes occurring in the steppe. Calcification and formation of calcic horizons are typical for loess derived soils. In the north-facing slopes of the Alborz mountain ranges with the forest vegetation and higher rainfall, deeper leaching of calcite and formation of the argillic horizon are dominant. The loess-paleosol sequences reflect diachronic changes in dust accumulation rates and testify formation of interstadial or interglacial paleosols at land surfaces of the Middle to Late Pleistocene. Pedostratigraphy backed by luminescence dating show a clear regional correlation of loess-paleosol sequences along the Alborz Mountains foothills. Strongly developed paleosols reflect major soil forming periods during the Eemian Interglacial (~MIS 5e) and during interstadials of the Early Last Glacial (~MIS 5c, 5a), while weakly developed palaeosols likely formed during interstadials of the last and penultimate glacials. Comparing with paleosol formation in the Iranian Loess Plateau it appears very likely that pedogenesis of interglacial paleosols was governed by similar climate-controlled trends to those reflected in the modern soils. The loess-palaeosol sequences represent excellent records of (Late) Quaternary climate change in the area.
References:Khormali F., Kehl, M., 2011. Micromorphology and development of loess-derived surface and buried soils along a precipitation gradient in Northern Iran. Quaternary International. 234, 109-123.Vlaminck, S., Kehl, M., Rolf, C., Franz, S.O., Lauer, T., Lehndorff, E., Frechen, M., Khormali, F., 2018. Late Pleistocene dust dynamics and pedogenesis in Southern Eurasia – detailed insights from the loess profile Toshan (NE Iran). Quaternary Science Reviews 180, 75-95.
