Investigation of Geology, Hydrology, Geomorphology, Mosques, and Morphotectonics of Jahangir Ancient Zone on the Margin of Kangir River, Eyvan, Ilam Province

Jahangir Site has been located at, 25-kilometer distance from the southwest of Eyvan city in Ilam province, and on the northern margin of Kangir River. The first archaeological studies in the area were conducted by VandenBerghe in 1970 . With the construction of Kangir dam for the prevention of water flow into Iraq, the ancient sites existing on its margin were put at risk. For this reason, the conduct of a rescue excavation was placed on the agenda of Iranian Center Archaeological Research. After the filling of the dam in winter 2015, a number of sites were immersed in water, and only Jahangir remained. some precious architectural and objects were found for the first time in Iran's Sassanid era by excavations in Jahangir. The analysis of these findings can provide the response for one of the important research questions and gaps pertaining to the transition period of the Sassanid era to Islam in western Iran. In addition to political factors, geography has been an effective and active contributor to the organization and decline in this site. This area is a part of Zagros folded zone that was studied in terms of the geological variables, including lithology, climatology, erosion, sedimentology, hydrology, and seismological investigation based on field evidence and observations, geological maps and resources, and by using the results of previous geological studies. The present paper is a report from the general interpretation of a site for archaeological purposes and for the development of its conservation plans. Based on the total of data and the interpretation done on the related studies presented in different parts of the current research, it is possible to reach a comprehensive analysis of this ancient site : The ancient structure is located on the second generation quaternary alluvium, which are the young fluvial terraces and alluvial fans. The quaternary sediments of the valley generally originate from the erosion of the rock of adjacent altitudes and older sediments of the valley basin, which have been transported and eventually deposited during various erosion periods. From the petrologic point of view, the area can be considered as a perfectly favorable area for erosion because its constituent formation includes a variety of loose and erosional forms, mainly made from anhydrite and red marl with lime intermediate layers. Anhydrite or gypsum has been employed to construct Jahangir monument, which easily erodes as a result of precipitation and acts very flexibly against tectonic pressure and, thereby, it gets deformed. It is noteworthy that marl is made of erodible sediments of soft silt and clay, which are used for flooring. The whole slopes of the zone inside the valley and the subarea No.5 are about 6% and 13%, respectively. These slight slopes lead to a calm flow with a low power of sediment carriage towards the river inside the valley. Therefore, the sedimentation power of the river and its canals in the adjacency of the ancient structure will be very high. According to the historical texts, two major earthquakes occurred in 3 & 4 centuries AH and the available data are consistent with earthquake studies in the database of seismology and building. Indeed, the majority of the historical recorded earthquakes in the area have been above 6 on the Richter scale in magnitude, which are classified into the category of dangerous earthquakes. This type of earthquake, due to its high kinesthetic power, has ruined the ancient structure and, thereby, the remains of each earthquake are visible in the form of cracks, collapsed walls, and tilted vertical and horizontal lines in the structure. Field observations of sedimentary layers, i.e. fillers of the interior space of the building, which have been obtained during the excavation include the constituent elements of sediments; and the proper layering, smooth slope, and consistency of the order of the sedimentary outcrop inside the building with other sedimentary outcrops around the zone indicate that this ancient structure has been influenced by the natural factors dominant over the region in the past decades. The sedimentary consistency suggests that the building has been buried under the influence of Kangir River, its floods, and sedimentation. Based on studies, water erosion and cross-sectional sedimentation are very active in the valley and this feature has become problematic for the ancient structure. In addition, rainfall and the passage of many surface run-offs during the year cause the simultaneous erosion of the building materials and walls (due to its gypsum type) and, on the other hand, it leads to its further deposition and burial. Its proximity to agricultural lands and residential areas as well as its situation near the dam are among the other human factors negatively affecting the survival and durability of this structure. Therefore, it is necessary to provide solutions to protect this structure against the natural and human threats imposed on it. By means of geological studies on historical eras, one can analyze the variety of variables involved in the construction of a building and its deployment in order to opt for a suitable Restoration of monuments method for its conservation.