Reconstruction of the paleo-environments of northern and southern slopes of the Alborz Mountain chain based on preserved evidence in soils

摘要

The purpose of this study was reconstruction of dominant paleo-environments on northern and southern slopes of Alborz Mountain based on the modern and old environmental evidences preserved in the soils. Totally 691 soil profiles in 14 separate segments (9 segments in northern slope and 5 segments in southern slope) with an area of 783,850 ha (251 pedons in northern slope with about 123,600 ha; 440 pedons in southern slope with about 660,350 ha) in Alborz Mountains were studied. Morphological, physical, chemical, mineralogical, micromorphological, and geochemical analyses of the studied sites carried out using standard methods and demonstrated significant differences between the soils of northern and southern slopes. Micromorphological data showed that the calcite coatings in northern slope pedons have formed before the clay coatings however, while the opposite conditionings for calcite and clay coatings in southern slope were observed. The geochemical analyses results were in agreement with the results obtained from micromorphological analyses and further confirmed the addition of aeolian materials into the studied pedons in southern slope. Biological features and the organic and inorganic residues were extremely different in the northern and southern slopes. The maximum and minimum mean residence times (MRTs) in the subsurface layers were 4467 +/- 50 years in deciduous forest and 4410 +/- 48 years in coniferous forest in northern slope. However, the MRTs for burnt woods from the depths of 1.6 and 2.68 m of soil in southern slope were 3665 +/- 61 and 6083 +/- 84 years, respectively. Soils as archives of ecosystems contain very informative data for paleo-environmental and paleogeographic reconstructions. The results of this study demonstrated that the southern slope has been heavily influenced by glacial and aeolian deposits that in some cases have led to the top-down reverse distribution of the element oxides in the soil.