بازسازي قلمروهاي مورفوديناميك بر اساس شواهد ژئومورفولوژي يخچالي و مجاور يخچالي (مطالعه موردي؛ كوه هاي چهل چشمه و سارال در استان كردستان)

Reconstruction of the morphodynamic zones based on glacial and periglacial geomorphology evidence)Case Study: Chehelcheshmeh and Saral Mountains in Kurdistan Province

ديناميك يخچالي و مجاور يخچالي نقش مهمي را در تحولات ژئومورفولوژي ايفا مي كند. هدف اين تحقيق بازسازي برف مرز كواترنر، بررسي آزمايشگاهي محيط رسوبي و شواهد قلمروهاي مورفوديناميك يخچالي و مجاوريخچالي كوه هاي چهل چشمه و سارال در استان كردستان است. در اين رابطه ابتدا سيرك هاي يخچالي با استفاده از تحليل نقشه ها و بازديد ميداني شناسايي شدند. سپس با روش خط تعادل آب و برف پورتر، ارتفاع 2483 متر به عنوان برف مرز دائمي كواترنري مشخص گرديد كه در مقايسه با كوه هاي زاگرس و البرز در ارتفاع پايين تري قرار گرفته است. جهت شناسايي محيط رسوبي نتايج عمليات آزمايشگاهي به صورت دانه سنجي غربالي و ليزري بر روي نمونه ها نشان داد كه منطقه مطالعاتي متاثر از فرايندهاي ناشي از انجماد و ذوب برف با حفظ بقاياي گياهي و توزيع ناهمگن و جورشدگي ضعيف ذرات مي باشد. در بررسي لندفرم ها شواهدي از جمله سيرك ها، دره هاي يخچالي، يخرفت ها، سنگ هاي سرگردان، ترك هاي سنگي، روانه هاي سوليفلوكسيوني، نهشته هاي بهمن و پلكان هاي سنگي شناسايي شدند. در بررسي توزيع اين شواهد به اين نتيجه رسيديم كه مرز تحتاني پريگلاسير تا ارتفاع 2750 متر قرار دارد.

The study of the past glaciers and its effects are the most important subjects of the quaternary period. The most important climatic evidence of the quaternary is also in the mountains of Iran، especially in the Alborz، west and northwest of the country is glaciers and related landforms. Geomorphologic studies focusing on glacial and periglacial landforms allow us to get a better insight into the spatial diversity of present and past climates. The Chehelcheshmeh and Saral Mountains are among the coldest mountainous regions in the country.These regions during the quaternary period was mainly influenced by glacial processes. The aim of this study was to reconstruct the quaternary snowline and morphodynamic zones based on glacial evidence. 2-Materials and methods: Chehelcheshmeh and Saral Mountains are located 46 degrees، 28 minutes to 46 degrees and 58 minutes east longitude، and 35 degrees and 34 minutes to 36 degrees north latitude. The method of this research is analytical-descriptive and data collection method is library and field. The data used in this study includes aerial images، DEM، topographic maps and geological maps، and analysis tools including Arc Map version 10 and Gradistat version 4 software. In this research to recreate the glacier zone we used Wright and Porter methods. The permanent snowline in the Wright method is equivalent to an elevation of 60% of the cirques in the area above that height. For calculation of ELA in the method of cirque-floor altitudes، a mode has been used for classified data. For laboratory studies in this research، we used two granulometry and microscopic methods for three sediment samples. For granulometric Process، we used Seave analyzes for particle with a diameter of more than 2 mm and Laser analysis for sediment grains with a diameter of less than 2 mm. Then، based on laboratory studies and field observations (to better control and identify the landforms) and with the help of aerial imagery، the study of elevational digital model and the study of geomorphologic landforms was identified evidence of each of glacial and periglacial morphodynamic zones. 3-Results and discussion: In the survey of the study area، 25 glacier cirques were identified، some of which are well seen by the surrounding landforms. Distribution of glacier cirques showed that the glacier extent was down to 1280 meters high. In accordance with the Porter's cirque floor altitude، the final limit of the quaternary snowline was 2483 meters above sea level، which considering the active glacier valleys، glacial evidence was also seen below this elevation. In the field observations، it was found that glacial deposits are located in the Ghezel Ozan river and at a height of 1900 meters. To determine the sedimentation environment، the results of Laser and Sieve analysis on the samples showed that the studied area is affected by the processes of freezing and melting in a cold environment by preserving plant remains and heterogeneous distribution and particles bad sorting. Maintaining feldspar minerals is another result of laboratory work، which indicates severe mechanical erosion and very low chemical erosion in the study area. The lack of clay and colloidal sediments confirms this.The glacial and periglacial morphodynamic zones in this research were studied using their evidence that was identified many of the relevant landforms including Cirques، Glacial valleys، Tills، Erratic rocks، Solifluction lobes، Rock cracking ، Moraines، Avalanches and Rock steps. 4- Conclusion: Investigation of glacial and periglacial evidence showed that quaternary snowlines in the mountains of Chehelcheshmeh and Saral compared to the investigations carried out on the Alborz، Zagros and central iran mountains at lower altitudes. Different climate of Kurdistan mountains compared with other parts of Iran is one of the main reasons for the low elevation of snowline in the region، so that the minimum temperatures in the synoptic stations of Zarrineh Obato and Heazrkanian that located in two catchment basins in the cold seasons it is mostly critical and one of the coldest parts of the country. Sedimentological evidence and laboratory analysis also indicate a cold environment in the study area mainly influenced by snow melting processes and mechanical processes، in many instances، irregular arrangement and bad sorting are observed and coarse particles constitute the highest weight percent. In the study of field evidence، many landforms and processes were identified that، considering the distribution of glacial evidence in the present، lower boundary of the periglacial morphodynamic active zone was introduced the 2750 contour.