Alluvial fan facies of the Qazvin Plain: paleoclimate and tectonic implications during Quaternary

The present research focuses on a detailed facies description and interpretation of five alluvial fans of the Qazvin Plain. Beside the tectonic activity that leads to the localization of the fans on the northern margin of the Qazvin Plain, the climate has a significant role in the occurrence of their facies. The alluvial fans are divided into three facies groups: group 1, group 2, and group 3. Alluvial fan 1 is dominated by the episodic matrix to clast-supported gravel, interbedded with a subordinate, and red matrix-supported gravel deposited by non-cohesive debris flow. Groups 2 and 3 are characterized by deposits of debris flow, mud-rich debris flows, channelized, non-cohesive debris flows, hyperconcentrated flows, and sheet floods. The hallmark of fan 3 is disorganized, very poorly sorted gravel, lack of erosional bases, and a wide particle-size range from clay to outsized-boulders. The facies interpreted as a result of debris flow following episodic localized tectonic activity of the Kavendaj Fault along the fan head during Quaternary. Relatively insignificant changes of the sedimentary facies of the studied fans from debris-flows to sheet floods during the accumulation of the three groups are attributed to a slight variation of climatic conditions, source rocks, and tectonic activity.