Reconstruction of Quaternary Urmia Paleo Lake level by studying Lake Terraces

Lake Terraces are geomorphological evidence of climate change during quaternary. Location of this terraces Location if these terraces in different elevation show paleo water lake level fluctuation. Investigation about Urmia Lake terraces was done by Bobek (1973) and he found that terrace in 45-55 meter above Urmia water level on that time. According to bobek development of lake area in paleo Pleistocene period and cold Pleistocene periods caused by reduction of temperature about 5 centigrade and reduction of evaporation. What is important in we have not any comprehensive investigation on Urmia lake terraces and many of these terraces and paleo shoreline are unknown up to now. The aims of this research investigation of quaternary terrace of Urmia Lake، Determining their elevations and reconstruction of area that affected by these fluctuations. Case Study: Urmia Lake Basin is located in Northwest of Iran and in the lowest pat of this subsidence، surrounding by High Mountain with elevation more than 2000 meter. Urmia Lake is the largest inland lake in Iran and the second largest saltwater lake in the world. In terms of construction، Tabriz fault activity causes uplift in this region of northern segment of the fault and the piece above by creating a barrier against the flow of surface and underground، has led to the formation of Lake Urmia. This lake is located in a shallow subsidence with an average depth of 6 meters، but its deepest point is the northwest corner with 13 meters deep. There are 102 large and small islands within the limits of the Urmia Lake. Salt water is more than 350 grams per liter. Data and Geological data، sediment and morphometric data were gathered through library studies and fieldwork. Then Quaternary sediments in the coastal zone boundaries were reconstructed and paleo lake boundaries using GIS and RS techniques were determined. Aerial photographs، satellite imagery and digital elevation model SRTM90 m was used and 10 Meter. In field work lake terraces were detected by investigation of sediment laminations، sedimentological characterizes such as، Granolometry، color، type، location of strata and specially fossils located in the sediment. Granolometry of sediments were done in sedimentology lab of Geological survey of Iran using Vibratory Sieve Sahker. Percentage of sand and silt determined and analyzed using Gradistat 4. Software and the curves were plotted. Binocular Microscope used for paleontology investigation. The elevations of terraces were measured with a differential global positioning System. After determining the height of the terrace، extent of Urmia la ke paleo water level determined using 150 topographic map sheet scale 1:25000 related to the block 1:250000 Tabriz، Urmia، Mahabad and Khoy a digital elevation model with a resolution of 10 m were prepared. Urmia Plao Lake extent was reconstructed on satellite images. In recent years، due to the occurrence of hydro- climatic droughts over the past few decades and extensive dam construction on the main river and high water evaporation، the lake area decreased، and have been significant changes in water level lake. The lake terraces are the best evidence to reconstruct the paleo geomorphological situation in coastal environment and occurrences of these terraces shows climate change and tectonic phases. Hence، Identification of the terraces lake Urmia Lake was performed to reconstruct the situation of paleo environment. In field studies، lake terraces were detected by geomorphological، sedimentary structures، sediments grain size and especially fossil collections in the sedimentary layers. Because many terraces are buried in the river sediments، they are very difficult to detect and only in trenches created by the river or human activities such as road construction are considerable. Using a sequence of periods of fluctuating water levels and long dry periods and wet -laying sedimentary sequence lake was reconstructed through them. After identifying the terraces geographic location and the exact height determined using DGPS. In field studies 32 lake terraces were found in Quaternary sediments. Lowest terrace are located in Islami Island in the 1297 meters altitude and the highest terraces in Damirchi with 1369 meters altitude. Elevation of lake terraces are varies from 1297 m to 1369 meter and consequently the areas affected by fluctuations in lake water levels were the different. The maximum extent of lake level fluctuation has occurred in the south part of Urmia Lake. In this region the slope is very low hence، the slightest change in the water level of the lake the large extent of this region be affected by water level fluctuation. In the northern and western parts of the lake due to the steep slope impact of water level fluctuations is low. At an altitude of 1297 meters (terrace Sh-1) area of the lake was about 9،658 kilometers. Extent of lake on that time increased about 6560 square kilometers compare to 2011. Gacha Bashi terrace (height 1311 m) in West Golmankhaneh Peninsula is dates by sabouri (2010) and results shows about 46،000 years before present. The elevation of the terrace after the gathering and corrects errors by GPS dual frequency edited to 1336. 6 meter. the elevation of this terrace almost equal to Schweitzer (1977) terrace that located in 60 meter above Urmia water level in 1977. This terrace belongs to the Wurm I by Schweitzer. At that time not only Minadoab، Malekan، Bonab، Azar Shahr، Naghadeh and Mahabad Cities buried under Urmia lake water، but also it reach near the Urmia city. The highest terrace is located near Tsuj (Ts-2) City in North West of the lake and parallel to Damirchi DM-1in North West of the malekan with elevation 1369 meter. The extent of the lake at that time was about 13141 km and the water reach to Tabriz city.