Paleogeomorphology of Basin Sabzevar and its role in identifying urban civilization

The lakes are considered as an instruments for recognition of the past environmental conditions in geomorphology and environmental sciences. They are important because of creating spatial identity for residents of their coastal zone. According to the article of "Lakes of the fourth era, the basis of the growth and expansion of civilization in Iran", the historic city such a Sabzevar has been located on the on the edge of a local lake that there was no trace of that lake today. Therefore, a scientific and field study to find evidence of this claim began with the question of whether Sabzevar was once located on the edge of the local lake? The Sabzevar hole is one of the areas where its social formations are well known in eastern Iran and according to the Tarikh-i Bayhaqi (6th century AH) its formations (with the same old name) still exist despite all environmental incompatibilities. The purpose of this study is to determine the "spatial identity" of Sabzevar and to test the reality of natural history of this city based on geomorphological, sedimentological and archaeological documents in relation to the theory of "Lakes of the fourth era, the basis of the growth and expansion of civilization in Iran" by phenomenological method. This article is a test to confirm or reject this theory in Sabzevar hole.

Phenomenological method from Isfahan school is a new method in geomorphology which has special steps and process. To address this issue phenomenologically, data from three areas of geomorphology, sedimentology and archeology have been used. Their interpretation and analysis have been integrated in 5 steps in Grand Theory. The most important variables used in the field of geomorphology are: - Elevation data and their analysis in spectral classification of lake terraces - Satellite image data for terraces identification - Archaeological data and social formations and analysis of their position relative to lakeside terraces - Sedimentological and gravimetric data, hydrometry and interpretation of sedimentary indices.

By using geomorphological, archeological, and sedimentological data at each step, information on the spatial identity of the Sabzevar hole was obtained. The boundary map of the Sabzevar catchment was obtained using digital data. Field surveys and digital data revealed two terraces in the Sabzevar hole which were plotted on the map. Then the data of 23 ancient hills, historical villages of 6th century AH, and 49 old and new villages with statistical interpretation method were obtained and then analyzed for these terraces, which confirmed the two terraces mentioned in the previous step. The water vector network is also studied in the holes which confirms the existence of a local lake in Sabzevar hole. The data of 5 sediment samples from the study area were also obtained in the laboratory. The result of the analysis of granulometric and their diagrams, calculating the sedimentary parameters of the samples and the hydrometric method of the two samples, all indicated the presence of a lake in the Sabzevar hole. Geological analysis, geomorphology of the Sabzevar hole, topographic line analysis and lake fissure location also confirmed the existence of such a lake in the area.

The geomorphic evidence and sedimentological analysis of the Sabzevar hole showed that the Sabzevar hole undoubtedly formed a lake during a period of the Quaternary period. We can generally conclude from this proposal: - The presence of the lake in the Sabzevar hole can be confirmed by geomorphology, sedimentology and historical evidence. - This hole has been fissured in the western part for some reason leading to the discharge of lake water into the central desert. - The largest social formation is the "Sabzevar Ghasabeh", which in historical books it is referred to as a city, but other formations in the area have now become urbanized by population law (for example, the villages of Davarzan and Sheshtamad becomes a city in 1995 and 1998, respectively, or the village of Roudab became a district in 1990). Therefore, it cannot be concluded that the present identity of these areas is similar to that previously determined by the lake.