عنوان مقاله [English]
Present Landform has been affected by climate conditions duration the time, and also the characteristics of sequence and periodicity of the condition. Thus, using the landforms, we can reconstruct climate condition and its changes. Geomorphological glacier relicts are one the most terraces that show the changes of climate in the past. Nevertheless, Central of Iran has located in a dry region at the moment, especially central of Iran, but there are some specified landforms in the region that represent spreading the glacier in the center of Iran in Pleistocene. These includes abrasive and depositional relicts. The goal of the study is the investigating of present landforms in the central of Iran-Kazab Basin in the west of Yazd City- to know processes that have created them in the past, especially the landforms that have created by glaciers. Kazab basin has located in the south-west of Yazd city in the west slopes of Shirkuh Mountain along 31° 53´ to 32° 7´of northen latitudes and 53° 52´ 42" to 54° 7 of eastern longitudes.
Materials and Methods
This research has been performed on basis of field studies and direct observation of glacial landforms. But, we studied topographical and geological maps, DEM, satellite images as well as aerial photographs, at first. The resulted information of the maps controlled with GPS System in the field. Then, we measured some boulders and pick up some sample of sediments and examine them in the geomorphological laboratory in the department of geograpgy in Yazd University.
Discussion and results
Findings show many landform that has created by a glacier morphogenetic system. These landforms was categorized in two classes includes abrasive and deposition processes. The relicts of abrasive of the glacier activity involve 28 small and great rcirques and some wide valleys as well that the width some of them reach to 200 meters in height 2000 meters. The most important of deposition traces of the glacier in the region involve tills, moraines, tillite and erratic stones. We have discussed both classes in more detail in the following:
-Cirques: using topographical map and its contours characteristics we marked cirques on the map. Cirques appear on the map with stretched contours as sinusoidal form. Accordingly, we defined 28 small and great rcirques, and then checked them on the field using GPS system. More of them have laid between 2000 to 2500 meters height.
-Glacial valley: A valley carved by glaciers is normally U-shaped. A glacial valley becomes visible upon the recession of the glacier that forms it. Glacier valleys are the biggest abrasive forms glacier in mountains that become broad towards peak. Because a glacier has a much greater viscosity and cross section than a river, its course has fewer and broader bends, and thus, the valley becomes straighter and smoother. In the Kazab there are 3 wide valleys that the Hamane Valley, in the west of the basin, is the greatest so that the width of it reches about 200 meters.
-Tills and moraines: Moraines are landforms created directly by glacier. In other words, moraines are a formation composed of unsorted and unbedded rock and soil debris called till, which was deposited by a glacier. After the retreat of a glacier the moraines remain as prominent features of the topography. Present moraine often have deposited in Pleistocene epoch. Kazab moraines usually have lay within main valley and include different sizes. They often observe between 1750 to 2050 meters as lateral, medial and terminal moraine. The medial moraines in the region are shown spiral hills with about one kilometer length and 20 M height. Besides, they are one of the most typical relicts of glacier in the center of Iran. The most properties of moraine are nonhomogeneous, angular, and have vertical direction to the river.
-Tillite: Sedimentary rock that consists of consolidated masses of unweathered blocks (large, angular, detached rock bodies) and glacial tills (unsorted and unstratified rock material deposited by glacial ice) in a Conglomerate form. The presence of tillites in a region provides evidence of former intense and widespread glaciation; recent tillites (about 10,000 years old) can be directly connected with glaciation, and Pleistocene tillites (10,000- 2,500,000 years old) can be convincingly related to glaciation. In other words, tillites are a kind of conglomerates that their sediment is created by glaciers. The rocks are deformed, poorly sorted and comprise quartz, feldspar and mainly sedimentary lithoclasts. The pebbles are relatively nonhomogeneous regarding their size. In the Kazab basin, tillites are observed in the left and right of the valley. In the region, tillites has located as terraces on both besides the river channel on the bedrock. They probability belong to the first glacial period that in another glacial periods sediments have stick together by calcium carbonate and established conglomerate and also has covered by tills and slopes sediment, they have remained unweather till now The height of the tillite layer in the Qezrabad valley is about 10 meters.
-Erratic stones: An erratic is a boulder transported and deposited by a glacier that differs from the size and type than the bedrock or native rock to the area in which it rest. Erratic stone are useful indicators of of former ice flow, and setting of glaciers. Erratic stones in the Kazab valley has located in three different height like 1750, 1850 and 2170meters that could show represent three glacial periods in the region by reducing their intensity from old to new.
Results show glacial traces for three periods In the Kazab basin in Pleistocene. Tillites and moraines located on them show two glacial periods at least, but the erratic stones, which has located in three different height indicates to three glacial periods. Besides, tills, moraine, tillites, wide walleyes, and cirques affirm glacial prevailing in the region. Nevertheless, granulometry studding on the medial moraines as well as tiillites confirm glacier processes in the region too.