Journal des sciences de la Terre et du changement climatique

Abstrait

A Model for Comprehensive Studies of Alluvial Fan Deposits, Case Study: Ramhormoz Mega- Fan in Southwest Iran

Saeid Pourmorad, Shakura Jahan

A diligent study of detrital sediments and especially alluvial fan sediments requires a comprehensive model from different sedimentological, geochemical, morphotectonic and environmental perspectives.Ramhormoz alluvial fans have been selected as a study site, which is located in southwestern Iran, next to Bakhtiari and Gachsaran formations. These alluvial fans have been studied from the perspective of sedimentology, geochemistry, hydrochemistry, neotectonics and environmental hazards.Studies show that grain size varies from gravel to clay/mud size. Based on field evidence, 10 lithophyses: Gh, Gci, Gp, Gcm, Gmg, Gmm (gravel), Sh, Sp, Sm (sandy) and Fi, Fm (mud) have been identified, of which five structural elements CH, GB, SG, SB, FF are formed. The presence of these structural elements indicates that these sediments were formed in a fluvial sedimentary system (of the cut type with gravel bed), where sediments were transported along gullies. Petrographic studies show that the most abundant sediments are calcareous gravels.This study show that the provenance of these sediments in Ramhormoz region are from Gachsaran and Bakhtiari formations. Sedimentological studies have led to the division of alluvial fans into three parts: proximal (near the origin), medial (middle) and distal (farther from the origin.The results of geochemical analysis show that calcium and magnesium oxides have the highest percentage of overall oxides in this region. In addition, the most abundant percentages of rare earth elements include elements like Ce, La, Nd, Y, and the most abundant heavy metals are Zn, Pb, Cu, and Cd. The correspondence of geochemical and petrographic data indicates the study area is in active continental margin. The study of environmental pollution with the help of geochemical data show that Ramhormoz region is in an alarming situation in terms of pollution caused by V, Ni, Pb, Zn and Cu elements.Mineralogical studies performed by XRD technique show that chlorite and illite are the most abundant clay minerals in the studied samples. In addition, hydrochemical studies show high hardness of groundwater in Ramhormoz area due to the presence of Gachsaran Formation and as well as high amount of sulfate, sodium and calcium in this region. Tectonic studies conducted in the study areas show that the most important tectonic element in Ramhormoz region include Ramhormoz fault, which is a Persian anticline directly related to the transport of sediments in this area.