Investigating the relationship between geomorphic factors and Paleo sea-level changes in the Caspian Sea with the settlement pattern of ancient sites in the east of Mazandaran province

Human interaction with the natural environment has undergone many changes from the past millennia to the present. But geo archaeological studies tell us that although this interaction has changed, the basis of human behavior with the natural environment has been almost the same and based on one thing: Knowledge of the natural environment. Areas located in the southeast of the Caspian Sea, in terms of the relationship between natural and archaeological factors, are one of the most complex areas in Iran. The purpose of this study is to investigate the relationship between geomorphic factors and Paleo sea-level changes in the Caspian Sea with the settlement pattern of ancient sites in the east of Mazandaran province.

At first, using Arc GIS software and the 30-meter DEM, elevation and slope maps was obtained and classified. Then, using satellite images, Google Earth software and topographic map of the area, geomorphological map was prepared and the location of ancient settlements in relation to the slope and elevation, as well as the distribution and density of ancient sites in various landforms were analyzed. After that, in order to investigate the effect of long-term changes in the CS level on the settlement pattern of ancient sites, first the researches in this field were collected and after creating a database of the Paleo sea-level changes in the CS, these changes were temporally accommodated to the ancient periods. Then, the coastline in each ancient period in relation to the location of ancient sites were analyzed.

With the distance from the coastline, the density gradually increases and in the range of zero to 15 meters, the density reaches its maximum. Increasing altitude with decreasing temperature, flat lands and suitable soil for agriculture and pottery and increasing distance from the sea as a rich source of food, has led to a decrease in the density of ancient settlements. As the slope increases, the conditions for establishing a settlement become unfavorable and the density of archeological sites in the study area gradually decreases. Also, the slope is an important factor in determining the land use and sloping areas may be prone to erosion if cultivated. The density of ancient sites on alluvial fans is higher than other landforms. In addition, as mentioned earlier, the densest elevation range is from 0 to 15, which corresponds exactly to the distal part of alluvial fans in the study area.In the Paleolithic period, the CS experienced a regression (-50m), also experienced high stands up to 0m during the Khvalynian transgression (Mamedov, 1997), but the ancient settlements of this period were not very affected by these changes due to their nomadic lifestyle. The EpiPaleolithic period coincides with the last Khvalynian transgression and CS level reached its maximum (+50). After that, the CS entered the regression phase of Mangyshlak and the maximum regression of that (-92m) occurred at this time (Kroonenberg et al, 2011). It seems that during this period, ancient communities built their settlements near the coastline, in order to have maximum access to the food resources. In the Neolithic period, the accumulation of ancient sites is in the coastal areas. With the advent of agricultural activity, coastal areas became more and more important to ancient societies and the reason is the presence of fertile soil, low slope and access to sufficient water and soil for agricultural activity and pottery. The maximum shoreline recedes during the Chalcolithic period occurred at 7100 BP (-36.5m) (Kroonenberg et al, 2008). And the greatest transgression has occurred in 7000 years ago (-20m) (Raychagov, 1997). This short period of time could have prevented ancient societies from adapting to environmental changes and many settlements near the coastline have been destroyed. In Bronze age, the CS level has fluctuated from -35.5m (Kroonenberg et al, 2008) to -21m (Mamedov, 1997). Along with the shoreline recedes, the settlements also advance towards the sea, and with the re-advance of the coastline, the settlements have been buried under sediments and water. During the later periods, there is an increase in the number of ancient sites in the highlands compared to previous periods. It’s may be due to military security issues during these periods. Because mountainous areas, with more difficult access than coastal areas, have provided more security for its inhabitants.

The purpose of this study is to investigate the relationship between geomorphic factors and Paleo sea-level changes in the CS with the settlement pattern of ancient sites in the east of Mazandaran province. The results show that as the slope and elevation increase, the conditions become unfavorable and the density of archeological sites in the study area decreases. in the range of zero to 15 meters, the density of archaeological sites reaches its maximum and this elevation corresponds to the distal part of alluvial fans where is the densest landform in the study area.One of the most important features of the study area is the intermittent changes in the CS level. After separating from the Black Sea in the Middle Pliocene, the CS has experienced several cycles of sea level fluctuation. In the Paleolithic period, ancient settlements were not very affected by these changes due to their nomadic lifestyle. But in the Epi Paleolithic period, it seems that ancient communities built their settlements near the coastline, in order to have maximum access to the food resources. In the Neolithic period, With the advent of agricultural activity, coastal areas became more important to ancient societies and the reason is the presence of fertile soil, low slope and access to sufficient water and soil for agricultural activity and pottery. During all periods, along with the shoreline recedes, the settlements also advance towards the sea, and then, with the re-advance of the coastline, the ancient settlements have been buried under sediments as well as the sea water. Moreover, in later periods, due to military security issues, the number of ancient sites in the highlands increased. Because mountainous areas, with more difficult access than lowland, have provided more security for its inhabitants.