تأثير عوامل محيطي در مكان گزيني استقرارگاه هاي باستاني در اطراف كهن درياچه هاي شمالي دشت كوير ( هولوسن)

The effect of environmental factors on the location of ancient sites around the ancient northern lakes of the desert plain (Holocene)

هدف اصلي اين پژوهش، شناسايي عوامل محيطي مؤثر در پراكنش مكاني - فضايي محوطه هاي باستاني در دامنه هاي جنوبيِ ارتفاعات البرز و حاشيه شمالي كهن درياچهِ دشت كوير در اواخر دوران كواترنري يعني دوره هولوسن مي باشد. لندفرم هاي شاخص با استفاده از عكس هاي هوايي، تصاوير ماهواره اي لندست و تصاوير گوگل ارث، شناسايي گرديد. سپس عمق كهن درياچه دشت كوير و سطح تراز تقريبي آن با توجه به يافته هاي پژوهشگران پيشين اندازه گيري و منحني تراز آن رسم گرديده و بر اساس مطالعات پالئوكليماتولوژي صورت گرفته پيشين، منحني تراز برف مرزهاي دائمي در اواخر دوران كواترنري محاسبه و به لايه هاي اطلاعاتي افزوده گرديد. در پايان، موقعيت مكاني و جغرافيايي استقرارگاه هاي باستاني به تفكيك دوره هاي تاريخي به لايه هاي اطلاعاتي فوق جهت تلفيق و تجزيه و تحليل نهايي اضافه گرديد. پس از تلفيق و روي هم گذاري لايه هاي اطلاعاتي بدست آمده در مراحل فوق، رابطه اي معنادار ميان جابجايي و پراكنش استقرارگاه هاي باستاني با تغييرات متناوب اقليمي و ژئومورفولوژيكي حاكم در اواخر كواترنري در منطقه مورد مطالعه بدست آمد. نتايج اين تحقيق نشان مي دهند كه پراكنش استقرارگاه هاي باستاني از يك الگوي پراكنش خطي و ارتفاعي تبعيت مي كنند.

Introduction Site selection of human habitats in pre-historic times, unlike the current periods, has been strongly influenced by natural factors. Studies may be focused on three areas including paleoclimate, paleogeomorphology and archeology in order to identify environmental factors affecting primary habitats. Based on studies, most of the ancient lakes in central Iran were formed during the Quaternary and were covered by sediments resulted from erosion of their adjacent heights. The research method was based on the methods of statistical analysis and spatial dispersion analysis of the aforementioned works and evidences and their comparisons in software environments with the capability of integrating information layers called Geographic Information System (GIS) and its compliance with field evidences. After integrating the layers of information, a significant relationship was found between the displacement and distribution of ancient settlements with the alternating climatic and geomorphologic changes of the late Quaternary in the study area. The results of this study show that the distribution of ancient settlements follows a linear distribution pattern and specific elevation levels. Objectives The main purpose of this study is to identify the environmental factors affecting the spatial distribution of ancient archaeological sites in the southern slopes of Alborz Mountains as well as the northern margin of the ancient lake, Kavir desert in late Quaternary, namely Holocene (Mesolithic and Neolithic, nearly 11000 years ago). Therefore, we tried to identify mentioned factors making use of paleontological evidences in four fields including epistemology, geomorphology, climatology and archeology. Methodology Research methodology is based on statistical and spatial distribution analysis of the above-mentioned evidences and their correlation in software capable to compile information layers in Geographic Information System (GIS) as well as their accordance with field evidences. Firstly, coastal landforms were identified making use of ETM+ Landsat images and Google Earth imagery and information layers were inserted to ArcMap environment. For this purpose, physical and conceptual tools such as 1: 100000 and 1: 250000 geological maps, 1: 50000 topographic maps, and 1: 55000 aerial photographs of 1335 were used in the study area. The archaeological site location data sheet (GPS) was prepared by the Archaeological Institute. Conceptual tools, such as ArcGIS software, for analyzing data and output maps, Excel software, for numerical and statistical computation and charting and charting required, Google Earth software, for using satellite imagery of the study area and digitizing some effects an‎d geographical phenomena were applied in the study area. Depth and approximate water table of assumed ancient lakes were calculated according to the findings published in previous studies and its contour lines was drawn and added to existing information layers. Discussion Based on previous paleoclimatological studies in this basin, snow lines for permanent boundary were identified in late Quaternary period and added to the existed information layers. Finally, the geographical coordination (GPS points) of ancient habitats was added to the above-mentioned information layers for integration and final analysis, separately based on historical periods (Middle and upper paleolithic). Compiling and overlaying obtained information layers, meaningful relationship was found between the displacement and distribution of ancient habits with periodic climatic and geomorphological changes in late Quaternary in the study area. Works and evidence in the study area show that the formation and development of the desert desert was dependent on the alternation of glacial and interglacial periods. The current pits' rims and evidences show complete synergy between the expansion of the Ice Age and the high level of lake water (Crinsley 1970). Lake Urmia also developed more during the Pleistocene during cold climatic conditions due to reduced evaporation (due to a decrease of about five average annual temperatures) (Bobek 1937). On this basis, it can be concluded that the sea levels of the Southwest Asian lakes, such as the Caspian lakes, Urmia, Fars, Van, have been declining and some of them have generally dried up. Past climatic evidence can be used to determine permanent snow boundaries and the extent of glacier expansion, as well as to study soil conditions over that period's climate. For example, Schweitzer now defines permanent snow altitude in the Alborz region of about 4,400 meters (Eivazi 1347: 74). There are different views on the boundaries of glacial expansion and the height of snow boundaries in central Alborz. According to Bobek and Schweitzer, the height of the snow in the Pleistocene cold period was about 800 to 1000 m lower than it is today (Eivazi 1374: 74 and 5), in central Alborz it was between 3200 to 3700 or between 3000 and 3500 meters. Ehlers (1960) considers the permanent snow boundary in the Pleistocene 200 meters below what Bobek and Schweitzer stated (Ehlers 1372: 107), namely between 3000 and 3500 or between 2800 and 3300 meters. Pedramia defines the boundary of permanent snow in recent Wurm in central Alborz about 2200 meters. Results The results of this study indicate that distribution of ancient habits follows a linear distribution pattern in specific elevation levels. Southern parts of Alborz consisted of several through during Quaternary that have been occasionally submerged by shallow and deep lakes during Quaternary. On the other hand, climatic changes have caused movement of permanent snow line in the Alborz Mountains. Location of habitats was constantly changing proportional to climatic conditions as well as surface topography such as slope and elevation from sea level. Therefore, early humans were migrating during different climatic periods (i.e. migrating to the summer and winter habitats). It seems that by restoring ancient lakes in the area, it may be possible to find more biological remnants from human habitats