Micromorphological analysis of loess-paleosol sequences in northern Iran: A case study of the Saadabad ۳ sequence

Loess and paleosols are terrestrial archives of past climate changes in arid and semi-arid regions of Asia. However, most of the available records are located in Central Asia and China, and few are available from West Asia. In this paper, we report a loess-paleosol sequence from the Gorgan Plain in the southeast of the Caspian Sea, named Saadabad ۳, which probably spans up to MIS۷. For this purpose, we identified and recorded ۵۶ horizons in the sequence wall and their characteristics, and collected intact samples from those horizons for thin section preparation. We also collected samples for physicochemical analyses from each horizon. Time and climate changes affect the soil micromorphology, such as bi-fabric, pedofeatures, microstructure, etc. Therefore, we evaluated this sequence in terms of micromorphology, secondary fabrics and physicochemical conditions. To establish a more reliable chronological framework, we compared the Saadabad ۳ sequence with two existing sequences in the Saadabad area ۱ and ۲. The results show that in the undeveloped horizons, with almost no secondary structure and massive texture, a dry and cold glacial period occurred, characterized by steppe vegetation and loess deposition. Climatic conditions in the developed soils, with channel voids, vughs, speckled bi-fabric and high percentages of iron and magnesium nodules and clay coatings and ... indicate wet periods. Our records indicate repeated dry and wet periods consistent with global MIS periods.

کلیدواژه ها:

Loess-paleosol ، Micromorphology ، Paleoclimate ، Caspian Sea ، Saadabad ۳