Paleoclimatic Changes and Research on Feasibility of Appearance and Development of Neolithic Societies in Gorgan Cultural Area

During the Holocene Epoch and simultaneously with the Neolithic Period, weather variations caused wide-ranging changes in temperature and humidity of various regions. These together with geographical and climatic features, led to the shaping of special regional matching of Neolithic cultures. We have obtained most of our knowledge of Epipaleolithic and Neolithic sites from excavations in locations on coasting regions bordering the Caspian Sea. Obviously, feasibility of relationships and population and information transfer between the mentioned regions is a research priority considering the role natural geography plays in the shaping of and developments in human communities. Available data includes climatic information from various sources such as magnetic analyses and geochemistry, paleoecology, palynology, study of oscillations in the water level of Caspian Sea, and sequences of loess sediments in the Gorgan Plain together with archeological data obtained from explorations made in the region. Considering the importance of developments in and environmental potentials of the region and their relationships with domestication of plants and animals, attempts were made to answer these questions through comparing and matching data obtained from reviewing studies carried out on oscillations in the water level of Caspian Sea, studies on soil sequences of loess sediments, and studies on archeological findings in the region.The study region is the cultural-geographical area of Gorgan that refers to a triangle in the southeastern corner of the Caspian Sea. The base of this triangle borders on the southern end of the eastern coasts and the other two sides meet the Alborz mountain range to the south and the Kopet Dagh mountain range to the east. The most important geographical feature of the Gorgan area, in addition to the Alborz and Kopet Dagh mountains, is the Caspian Sea that is fed by river sources in Iran and Russia. Presence of coastal sediments is the other feature of the region, and these sediments are derived from the rivers and aeolian loess belts. One of the strategies for paleoclimatology of the region is the study of alternate oscillations in the water level of the Caspian Sea that has yielded various results. The Caspian Sea region has experienced numerous alternate advances and recessions during the years. Moreover, soil studies have also provided interesting results. The loess formation in the region is in the form of the hilly areas in Gorgan and results from aeolian deposits of the last glacial recession in the Quaternary Period. Rereading archaeological data of the region and matching it with ancient weather can provide us with important information. Classification of Epipaleolithic layers in the Hotu and Belt caves can be matched with ancient weather and be confirmed by advances and recessions of the Caspian Sea. The present conditions indicate that the region faced hard and harsh conditions at the start of the Neolithic Period. Evidence of deep gaps between dating of the Hotu and Belt caves and evidence of plant and animal domestication and of pottery, and accumulation of aeolian loess sediments are among the available reasons for confirmation of population transfer. Another reason supporting this claim is that the Pokerdval area in the Gorgan Plain with materials and pottery of the Neolithic Period, that have great similarities with the oldest samples of the Tappeh Sang-e Chakhmagh and the Hotu and Belt caves, lies one yellow layers of loess that probably match the second advance of the Caspian Sea during the Holocene Period. Therefore, this set of information shows that cultural and technological developments in the human communities of the region strongly depended on conditions imposed by the environment, and severe environmental fluctuations necessitated continuous population movement, which caused infiltration of cultural material beyond geographical borders and created the relative homogeneity between the potteries attributed to the Jeitun Culture. Based on present documents, population mobility was one of the features of this region in Late Pleistocene and Early Holocene Periods.