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عنوان مقاله [English]
Investigation of river terraces is one of the main issues in the field of river geomorphology. River terraces, as a medium of alluvial landforms and heritage of stratigraphy, are widely investigated by geomorphologists to understand the tectonic and climatic time. The formation of alluvial terraces is primarily the result of tectonic rise alongside the cycling cycles. The edges of a river that is hard and resistant to geology are wall-bound or steep sloping, similar to water-breakers, and limit the number of the steppes to the alluvial terraces; but on the sides with a looser lithology, alluvial terraces are formed with a slight slope. Go up or down to the basin or the sea level changes are accompanied by a change in the slope along the river, creating tectonics alluvial terraces. Ghezel Owzan River, as one of Iran''s longest river systems, has well responded to lithological and tectonic factors. The Ghezel Ozan Basin is located in the northwest of Iran, and in latitude of 34° 53'' 21" to 37 ° to 56'' 2" north and longitude is 46 ° 27'' 43" to 49 ° 19'' 43 "east. The origin of the Ghezel Ozan River is from the heights of Chehel Cheshmeh Kordestan and with a length of more than 550 km, after crossing Zanjan, East Azarbaijan and Ardebil provinces, along with several streams along its path, intersects in the Guilan province with the river Shahroud and enters the reservoir of the Sefidrood Dam.
Accordingly, river terraces are lithologically divided into marl, crystallized and conglomerate periods with the help of geological (1/100000) and topographic (1/50000) maps and using computer software such as Arc, GIS, Global Mapper, and Excel. River path is also lithologically and tectonically divided into eight periods and profiles of each period are drawn. In order for the collection of information, we have translated several English articles and examined various internal sources related to the subject matter of the research. With the help of geological maps and field observations of the region, we investigated the effect of tectonics and lithology on topography (symmetric-asymmetric) on alluvial terraces. Using the Global Mapper, the cross-sectional profile was mapped along the river''s perpendiculars and analyzed.
Results show that from among the major lithologies of Ghezel Owzan terraces (marl, crystallized, and conglomerate), marl terraces are more asymmetric and crystallized terraces are more symmetric in areas without tectonic movements. Symmetrical terraces are formed in areas without tectonic movements or in areas with the same tectonic movements on both sides with resistant lithology. Asymmetrical terraces are also formed in areas where tectonic movements are not the same on both sides or in areas where there are marls in-between geological layers. Marl lithology, which is the dominant lithology of the basin, has the greatest impact on the asymmetry of terraces on this river. Tectonic has been active in A, C, E, F & H periods and inactive during B, D & G periods.
Discussion and Conclusion
On the bed of the Ghezel Ozan River and major parts of Dyvandra to the Miyaneh, Qareaghaj and the greater part of the province of Tarom, it is overcome with Marl Lithology (Hashtchin to Khalkhal, upper and lower part of Hashtrood and Turkmen Chay, southern provinces of Miyaneh and Zanjan, middle section of Sojas). The conglomerate sediments are the dominant lithology of Qazlazan from Soltaniyeh to Nikpay and the upper of most major branches. The irregular dispersion of lithology and faults in different parts of the Ghezel Ozan River makes it impossible to sequentially divide the alluvial terraces. In resistant lithology, alluvial terraces of symmetrical are formed and in the marl lithology, the slope of the arches of the arches provided the possibility of a deep cut and, with deep erosion and common landslides in the transverse surfaces, low-calorie alluvial terraces is created with low altitude difference. Another factor in the asymmetric of the alluvial terrace is the lithology of the basalt and limestone of the Ghezel Ozan River terrace that act as a barrier and by reducing the river slope and reducing the erosion of the water, the river is forced to move horizontally before the strait, the degradation of the compressive levels has led to asymmetry of the terraces and denser plains.