Lithostratigraphy, petrography, and geochemistry of sandstone in the middle part of the Upper Red Formation, Ghezeljeh area, NW Zanjan

Ghezeljeh area is located in the northeastern part of Mahneshan at 70 km northwest of Zanjan. The rock units exposed in the area are including the Lower Red, Qom, and Upper Red formations which the Upper Red Formation is the purpose of current research. According to field studies, the Upper Red Formation with 750 meters thickness includes 250 meters of evaporative units with intercalations of marls at the bottom and 500 meters of alternation of marls and sandstones intercalations at the top. According to microscopic studies, the grain size of the studied samples ranging from very fine sandstone to gravel. These sandstones show poorly orientation and well to poor sorted and are angular to sub-angular. The sorting and roundness parameters as well clay content show that these sandstones are immature and in some cases are sub mature. Based on a high percent of components and the Folk classification, the middle part of the Upper Red Formation displays lithic-arenite (sed-arenite) and feldspathic-lithic-arenite with an average composition of Q38F15Rf47. Geochemical studies show that these sandstones sourced from intermediate to felsic igneous rocks and deposited on the active continental margin. Furthermore, the weathering index shows an arid and semi-arid climatic condition during their deposition.