Investigating temperature-dependent magnetic susceptibility and color measurement changes in a loess-paleosol sequence, Northern Golestan province, Iran

During the Quaternary period mid to high-latitude areas were affected by loess deposition. In Iran's northern and northeastern regions, significant loess deposits are prevalent and distributed throughout the Iranian Loess Plateau and along the northern foothills of the Alborz Mountains. Intercalated within these loess deposits are paleosols, formed during warm and moist climatic conditions (interglacial period). These paleosols offer an opportunity to study the climatic and environmental changes that occurred during the Quaternary period. Understanding the relationship between loess deposition and paleosol formation can offer significant insights into the mechanisms that drive changes in global climate and how they affect the Earth's geology and ecosystems. Studies have shown that loess sediments and loess-derived soils contain different concentrations of iron minerals such as hematite, iron oxyhydroxide, and goethite. These minerals are highly sensitive to environmental changes, and evaluating the changes of these minerals in loess-paleosol sequences can be a valuable indicator for studying paleoenvironmental changes. The two main minerals that cause color and magnetic susceptibility changes in loess-paleosol sequences are goethite and hematite. Therefore, the assessment of loess-paleosol sequences from the aspect of magnetic and colorimetric parameters provides the possibility to identify paleoenvironmental and climatic changes. The main goal of this research is to investigate the changes in iron oxides in the loess-paleosol sequence in the east of Golestan province using colorimetric techniques and temperature-dependent magnetic susceptibility in order to provide enough information for reconstructing the paleoclimatic conditions during the formation of paleosols.

Sampling was performed from the loess-paleosol sequence in the eastern Golestan province, for each loess and paleosol horizon. Initial colorimetric and magnetic susceptibility measurements were carried out respectively for 1345 and 24 samples at LIAG Institute in Germany. Color measurements were carried out with a spectrophotometer machine that covered the visible light range. The temperature magnetic susceptibility was carried out using in the 20–700°Ctemperature range in an argon atmosphere to minimize oxidation.

According to the results of this study, we can mention the identification of iron minerals in loess and paleosol samples using colorimetric analysis. Iron minerals such as hematite, goethite, and maghemite can be detected at wavelengths 565, 435, and 595 nm, respectively. Colorimetric results showed that the ratio of hematite to goethite of paleosols has increased compared to loess sediments in the study area, which indicates the increase in precipetation and soil moisture during the interglacial period. The heating curve (temperature-dependent magnetic susceptibility) of loess samples at 560-590 degrees Celsius showed a sharp decrease due to magnetite minerals in these samples. At the same time, this happens in paleosols at a temperature of 300-350 degrees Celsius, which is due to the loss of the maghemite mineral formed during the interglacial period. The results showed that the decrease in the heating curve in paleosols indicates the increase in the intensity of soil-forming processes.

The results of this study showed that iron minerals such as magnetite, maghemite, hematite, and goethite in loess and paleosols play an important role in magnetic properties and soil color. Also, the increase in the presence of hematite and maghemite in paleosols indicates the increase in the intensity of soil formation processes and humidity during the formation of paleosols. The results of this research showed that the colorimetric technique, along with temperature-dependent magnetic susceptibility, can be one of the fast and accurate methods in studying and identifying paleosols.