The present study provides a detailed facies description and interpretation of five alluvial fans of the Qazvin Plain. In addition to tectonic activities, which lead to the localization of the alluvial fans on the northern margin of the Qazvin Plain, climate also plays a significant role in the occurrence of facies in these fans. The alluvial fans are divided into three facies groups: group 1 (alluvial fan 1), group 2 (alluvial fans 2, 4, and 5), and group 3 (alluvial fan 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 non-cohesive debris flow, mud-rich debris flows, channelized, non-cohesive debris flows, hyperconcentrated flows, and sheetfloods. The characteristics of alluvial fan 3 include highly disorganized deposits, very poorly sorted gravel, lack of erosional bases, and a wide particle-size range from clay to outsized-boulders. The facies is best interpreted as a result of debris flow following episodic localized tectonic activities of the Kavendaj Fault along with the fan head during the Quaternary Period. Relatively insignificant changes in the sedimentary facies of the studied fans from debris flows to sheetfloods during the accumulation of the three groups are attributed to a slight variation of climatic conditions, source rocks, and tectonic activities. Therefore, the debris flow-dominated fans of the Qazvin Plain recorded an arid to semi-arid paleoclimate characterized by the generation of non-cohesive debris flow and calcrete in the fans.
