شواهد يخچال هاي كواترنر پاياني در حوضه تنگوييه سيرجان

Last Quaternary Glaciers Evidence in the Tangueeyeh Basin Sirjan

وجود آثار يخچالي به عنوان يكي از مواريث اقليمي كواترنر در سرزمين ايران نشان دهنده حاكم بودن يخچال ها در بخش هاي مختلفي از ايران در گذشته محسوب مي شود. لذا با توجه به اين آثار و شواهد مي توان شرايط اقليمي گذشته را بازسازي نمود. هدف از اين پژوهش شناسايي شواهد يخچال هاي كواترنر پاياني در حوضه تنگوييه سيرجان مي باشد. نقشه هاي توپوگرافي، تصاوير ماهواره اي و داده هاي اقليمي ابزار و داده هاي مورد استفاده در اين پژوهش مي باشند. همچنين جهت تجزيه و تحليل داده ها از نرم افزار هاي ARC GIS، SURFER و GLOBAL MAPPERاستفاده شده است. شناسايي شواهد يخچال هاي كواترنر مشتمل بر 4 دسته از شواهد بود كه عبارتند از: شاخص هـاي مـورفيك، شواهد اقليمي، شواهد ژيومورفولوژيكي و شاخص هاي آزمايشگاهي. با استفاده از شاخص هاي مـورفيك (فرم خطوط منحني ميزان بر روي نقشه هاي توپوگرافي) و تصاوير ماهواره اي، نواحي تحت سلطه پهنه هاي يخي و آثار 251 سيرك يخچالي شناسايي شد. شواهد اقليمي نشان دهنده اين است كه حوضه تنگوييه نه تنها در كواترنر حدود 9 درجه نسبت به زمان فعلي سردتر بوده بلكه بارش آن نيز نسبت به زمان حال تقريبا دوبرابر بيشتر بوده است. از طرفي سيرك هاي يخچالي، دره هاي يخچالي و يخرفت ها به عنوان مشخص ترين شواهد ژيومورفولوژيكي يخچال ها در حوضه مورد مطالعه شناسايي شدند. در نهايت شاخص هاي آزمايشگاهي (گرانولومتري ) به عنوان تكميل كننده شواهد يخچال ها، وجود رسوبات يخچالي را در حوضه تنگوييه به اثبات رسانيد. همچنين با استفاده از روش رايت خط مرز برف دايمي در دوران حاكميت يخچال ها در حوضه تنگوييه در ارتفاع 2719 متري و به روش ارتفاع كف سيرك پورتر در ارتفاع 2714 متري تخمين زده شد.

Introduction Among the environmental issues which attract researchersʹ attentions is the issue of climate changes; and geomorphology is among the sciences which pursues these changes based on geomorphic pieces of evidence (Pedrami, 1988, as cited in Amir Ahmadi, 2011). The quaternary climatic changes were known based on the morphological effects of glaciers for the first time in Europe and later the evidence related to these phenomenon was investigated on the other parts of the earth. In Iran, like other arid and semiarid parts of the world, the effects of these changes are known; however, regarding there are ambiguities as to the dominating conditions of climate over Iran in that period and its rage of changes (Ramesht&Kazemi, 2001). Although the present situation of Iran and domination of arid and semiarid conditions result in doubt regarding the presence of glaciers in this land, but the presence of evidence and geomorphological effects of glaciers in various regions of Iran indicate the performance of these glaciers in these regions (Vaziri, 2003; as cited in Ramesht et al. 2011). Objectives The objective of the present study is to identify the evidence of performance of quaternary glaciers in the Tangueeyeh Catchment of Sirjan. Methodology To identify the evidence of quaternary glaciers in the Tangueeyeh Catchment of Sirjan began with limiting the boundary of the studied catchment with regard to topographical maps 1:50000. In this line, using meteorological data and DEM of the catchment, raining and the present temperature of the catchment was drawn by ARC GIS software program. In the next stage, regarding the form of rate curve on the topographical maps 1:50000 and satellite images of the regions dominated by ice zones and glacial cirques were identified; and of the past permanent snow line of Tangueeyeh Catchment was estimated by Wright and Porter method. Then, using the altitude of past snow line and adiabatic temperature drop, the isothermal map of the past catchment was provided. To provide the past precipitation map after covering the present isothermal and precipitation maps of the catchment in ARC GIS, the point bi-serial correlation was valuated and using the relationship between the present precipitation and the temperature and the past thermal data, the past precipitation map was provided. In the next stage, in the field operation of the geomorphological forms built due to the process of glaciers were identified and regarding the principles of the sampling, certain parts of Tangueeyeh Catchment were sampled and granulometry experiments were conducted on sediment. Results and Discussion Morphic evidence (the form of rate curve on the topographical maps): the regions dominated by ice zones in the past time are of the cases which can be identified using the form of rate curve in the topographical maps. These regions are reflected on the topographical maps in the form of sinus lift or sinus graft with large wavelength on the level curves. In a lot of parts of topographical maps of the catchment, this kind of form of rate curve is observed, which itselfis the reason of the plate movement of ice in Tangueeyeh catchment. In addition, using evidence of the soleus form of rate curve on these maps, the evidence of 251 glacial cirque were identified. Estimating the permanent snow line of the catchment in quaternary using wright method and Porter cirque floor altitude method Wright method which is known as one of the methods of determining permanent snow line is based on small cirques and their altitude of outlet orifices (Ramesht&Poordehghan, 2009: 133). According Wright method, permanent snow line in the late quaternary was estimated in the altitude of 2830 m. According to Porter cirque floor altitude method, when a glacier only fills the cirque, its permanent snow line is not much higher than the man of cirque floor altitude. According to this method, the permanent snow line in the late quaternary was estimated in the altitude of 2714 m. Climatic evidence The conducted studied indicate that in the late quaternary, the minimum mean and the maximum of temperature in the catchment were -9.5 and 6 centigrade respectively, while the maximum mean and the minimum of the present temperature of the catchment is 14.6 and 1 centigrade respectively. In other words, Tangueeyeh catchment in the late quaternary was about 9 degrees colder than the present time. In addition, the minimum and maximum amount of precipitation in the late quaternary were 450 and 850 mm, while the minimum and maximum of the present precipitation were 173 and 513 mm. Geomorphic evidence Glacial cirques, morins, large parts of moraines and glacial valleys are of the most important geomorphic evidence which confirms the presence of the process of glacier in the late quaternary in Tangueeyeh catchment. Experimental evidence Conducting granulometry experiments on sampled sediment indicates that sediments are glacial nature. Conclusion Conducted studies indicate that the late quaternary of permanent snow line in Tangueeyeh catchment was located in altitude of 2719 m (using Wright method) or (2714 m). In addition, regarding the morphic, climatic, and geomorphic and experimental evidence one can claim firmly that Tangueeyeh catchment of Sirjan in the late quaternary was influenced by focused and plated movements of ice.