Sedimentology, facies and depositional model of Qazvin alluvial fan

Qazvin alluvial fan is the largest alluvial fan in the northern margin of the Qazvin Plain. This research focuses on describing and interpreting the origin of the sediments and facies model of this alluvial fan using 24 sediment samples from 11 sections and two surface samples. The results of facies granulometry show that the size of the sediments of the alluvial fan shows wide variations from gravel to clay, and the texture of the sediments of this alluvial fan is mainly gravel, gravelly sand and sandy gravel with very poorly sorting and fine skewness. The sedimentary rock fragments are mostly igneous and limestone. Facies study led to the determination of eight facies including coarse to medium-grained lithofacies (Gmp, Gcp, Gcp-Gmp/Sm, Gmg, Glns, Spl, and Sm), and calcrete facies (P) which grouped into two facies association. The results of this study show that the Qazvin alluvial fan can be considered a waterlaid-dominated alluvial fan due to the superiority of fluvial facies and the absence of the episodic matrix to clast-supported gravel (interbedded with a subordinate) and red matrix-supported gravel.