Investigation of Sedimentary Environment Changes in Quaternary Deposits of Mahdasht Alluvial Fan

Due to Quaternary climate change, many soils in the form of sediment, by various forms of erosion, have entered the exploration cycle or sedimentation. One of the forms of river sedimentation is alluvial fans. The Mahdasht alluvial fan in the south of Karaj was the remnant of climate changes in Quaternary. The aim of this study was to give an overall result of environmental changes in the region by investigating the changes in soil texture, pH and color in the sedimentary layers of Mahdasht alluvial fan.

The present study is fundamental in terms of purpose and causal-comparative and survey in terms of methodology. Its information has been collected by documentary, field and laboratory methods. In order to achieve the desired purpose, 19 samples were taken from a 5-meter trench and in the laboratory, using the granulometric test screening, determining the pH of the sediment and color of the soil was exposed. After the experiments, the obtained data were analyzed.

The obtained results showed that among the sedimentary layers of alluvial fan, layer A2 with high thickness had the most difference of texture with other layers. In general, fineness, very low alkalinity and pale yellow color with high purity have been prominent features of the study layers.

The obtained evidence showed that the fluctuations and environmental changes of the late Quaternary periodically from the types of flood flows with medium to low energy, indicate the hot and dry period. Inter-channel facies in the alluvial fan include high-energy, medium, and low-energy channel currents. The upward medium-current flow, traced on horizon A2 with a thickness of 159 cm and three sedimentary sources, indicates uniform, continuous, and long-term precipitation, and it can indicate cold and wet weather.