نوع مقاله : مقاله پژوهشی
1 دانشگاه شهید بهشتی
2 دانشگاه تهران
3 سازمان زمین شناسی کشور
4 دانشگاه ETH زوریخ
عنوان مقاله [English]
Marine and lake terraces are one of evidence for Climate Geomorphology investigationsEspecially in Quaternary. These Terraces are important not only for climatic aspects but also they can show a lot of truth about earth and environment evolutions History, Archeology and Human History. Marine and Lake Terraces are located in different elevations and these changes can present paleo water lake level fluctuations. Urmia Lake is a hyper-saline lake in northwestern Iran near Iran’s border with Turkey. The lake is between the Iranian provinces of East Azerbaijan and West Azerbaijan. It is the largest lake in the Middle East and the third largest saline lake on earth. Urmia Lake a Terraces are one the most important geomorphic evidences of this lake and show paleo lake level fluctuations of this lake in Quaternary. Investigation of these lake terraces from view of sedimentological and paleo lake level fluctuation This research was done with focus on identification relation between Urmia Lake level fluctuation and their effects on sedimentological characteristics of Lake terraces.
Materials and Methods
In this research Quaternary sediment boundaries in coastal plain and paleo Lake Coastline were mapped on satellite Images using GIS and Rs for study area. In field work, Paleo lake terraces identified and recorded. Lake terraces sampling were done according to granolometry, color and specially microfossils of sediments in field work. The elevations of terraces were measured with a Differential Global Positioning system (DGPS). Granolometry of the sediments were analyzed and Percentage of Clay, Sand and Gravel were determined in sedimentology lab of Geological survey of Iran using Vibratory Sieve Shaker. Percentage of Silt and Clay Determined Laser Particle Sizer. Granolometry data analyzed in Gradistat 4 software and the curves were plotted. Geochemichal Investigation was done Using ICP and XRD analysis to determination Chemical Elements of sediments. Granolometry and Geochemical Information Stratigraphy Plotted using Logplot Soft ware.
According to the results of granolometry studies Represent 45/6 Percent of lake sediments are located in range of mud, 42/6sand and 11.8 gravel. 90/8 percentage of sediments particles included in Mud and sand. The most frequent of sediment types are Slightly Gravely Sandy Mud and Slightly Gravely Muddy Sand. Geochemical data shows when water lake level rose, sediment environmental changed from terrestrial sediments to lake environments and at this time rate of geochemical elements change. Percentage of CaO elements increase during water level rise and decrease when water lake level down. Magnesium calcite is high in almost all lake terraces sediments and Most of lake terraces sediment samples have Biotic Calcite. The study concluded that the increase of CaO can be very much dependent on biological content and increasing the amount of micro- fossils in Lake Terraces sediments.
Conclusion High volume mud in lake terraces sediments samples represent , lake terraces formed in a low-energy environments like as lake , wetland or local closed holes. Increase the amount of CaO in lake sediments terraces in most cases due to the increase in deposits of shells, including chemical and biochemical sediments that contain calcium carbonate, respectively. High magnesium carbonate deposits lake terraces in lake sediments can be very high due to the size and role in skeletal shells in the lake sediments. Probably Urmia lake many terraces, especially those who have very thick stratification (over 100 cm), as well as terraces Kachabashi, Naghadeh, and Qez Qaleh are formed in south part of Urmia Lake