نوع مقاله : مقاله پژوهشی

نویسندگان

1 گروه زمین شناسی، دانشکده علوم پایه، دانشگاه آزاد علوم تحقیقات تهران و سازمان زمین شناسی و اکتشافات معدنی کشور

2 رسوب شناسی، دانشکده علوم زمین، دانشگاه خوارزمی تهران

3 پژوهشکده علوم زمین، سازمان زمین شناسی و اکتشافات معدنی کشور

4 رسوب شناسی، گروه زمین شناسی، دانشکده علوم پایه، دانشگاه آزاد علوم تحقیقات تهران

چکیده

مطالعات بین‌رشته‌ای نقش مهمی در پاسخگویی به سؤالات پروژه‌های مهندسی بازی می‌کنند. مطالعات تلفیقی رسوب‌شناسی و ژئوالکتریک برای بررسی پراکنش انواع رسوبات دو سوی غربی و شرقی بخش جنوبی دریاچه ارومیه، نقش آن‌ها در تبادل آب‌های زیرزمینی و وجود گسل در بستر دریاچه انجام شد. بدین منظور 18 گمانه 10 متری در سه پروفیل در دو سوی دریاچه حفاری و رسوبات ستون چینه‌شناسی آن‌ها تحت آزمایش دانه‌بندی و کانی‌شناسی و تطابق قرار گرفت. تعداد 391 سونداژ ژئوالکتریکی قائم با آرایه شلومبرژه در دشت‌های حاشیه برداشت شدند. ستون دانه‌بندی گمانه‌ها با سونداژ مجاور متناظر شد و با تصحیحات نرمال‌سازی، به روش دیفیوژن، درون‌یابی و نقشه‌های هم‌مقاومت ترسیم و تفسیر شد. در 5 مقطع عرضی، برش‌هایی از غرب تا شرق دریاچه تهیه و تغییرات دانه‌بندی و مقاومت الکتریکی در آن‌ها بررسی شد. نتایج نشان داد در دو ناحیه، به دلیل وجود رسوبات درشت‌دانه و دارای مقاومت الکتریکی بالا، امکان تبادل آب‌های زیرزمینی وجود دارد. این نقاط می‌توانند مسیل‌های قدیمی رودخانه شهرچای و باراندازچای و انشعابات آن‌ها بوده باشند. به دلیل تمایز بالا و اختلاف مقادیر دو پارامتر مقاومت الکتریکی و مغناطیسی در دو سوی دریاچه، یک گسستگی ژئوفیزیکی در دو روش ژئوالکتریک و مغناطیس‌سنجی هوایی در محل دریاچه قابل اثبات است.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Integration of sedimentology and geoelectrical studies in Quaternary deposits in western and eastern coastal areas of southern part of Lake Urmia

نویسندگان [English]

  • Shohreh Erfan 1
  • Khalil Rezaei 2
  • Razia Lak 3
  • Sayyed Mohsen Al Ali 4

1 Department of Geology, Faculty of Basic Sciences, Tehran Azad University of Research Sciences and Geological Survey of Iran

2 Sedimentology, Faculty of Earth Sciences, Kharazmi University, Tehran

3 Research Institute of Earth Sciences,, Geological Survey of Iran

4 Sedimentology, Department of Geology, Faculty of Basic Sciences, Tehran Azad University of Research Sciences

چکیده [English]

Extended Abstract
1-Introduction
Interdisciplinary studies play an important role in answering engineering questions. Identifying the characteristics of alluviums, underground water exploration and minerals, along with geotechnical studies in the construction of heavy structures are just some of these applications. Following the increasing drying of Lake Urmia, various research has been conducted to answer multiple questions posed by the agenda of various organizations. The two most important questions in the set of questions were that: 1. Is the water of Urmia Lake connected to the subterranean sediments of the two sides with the wells of the region and where is the location of this exchange and passage of the subterranean saline and fresh waters in which regions?2. Is there a fault under the lake? To answer these two questions, geological and geophysical surveys were planned and designed with financial constraints. In this research, sedimentology and Geoelectric studies with the aim of investigating the distribution of various sediments in the western and eastern margins of the southern part of Lake Urmia, their role in the exchange of groundwater between the lake and the wells of the marginal plains, as well as the presence or absence of faults in the lake bed was done.
 2- Material and method
Lake Urmia is located in north west of Iran and in Azerbaijan province. This lake is one of the most saturated lakes in the world and the largest and warmest permanent lake in Iran. This is a lake with fresh water that gradually salted to an overestimation of salt. In this study, 18 boreholes of 10 meters were drilled in three profiles along the lake, and the stratigraphic column of sediments within them were subjected to granulation and mineralogy experiments and adapted to each other. A total of 391 Schlumberger Geoelectric vertical soundings was taken and interpreted in marginal plains. The grain size column of the boreholes was fitted with adjacent soundings. The data were analyzed using standardized variables and statistical maps. Then, after analyzing the statistical ground by two GS + and ARCGIS software and calculating the statistical parameters and normalizing the data. The data were interpolated using diffusion method and the iso-resistivity maps were interpreted. In five cross sections, from west to east of the lake were prepared and the gradient and electrical resistance changes were investigated. Finally, these maps were compared with the map of the report of aerial geophysical studies (magnetism) and final conclusion was made.
3- Result and discussion
By examining boreholes, it was found that in terms of grain size, in almost no specimens, very coarse gravel particles were found and fine grains and clay minerals had the highest frequency. At some depths, due to the increased energy of the sedimentary environment, the sands suddenly increased and may indicate an increase in rainfall and the flow of rivers and streams. An increase in evapotranspiration minerals is also found in some depths that are consistent with the dryness of the environment and the reduction of precipitation. In the boreholes corresponding to Geoelectric assays, the effect of water table can be clearly observed in the change of electrical resistivity. The presence of clay causes relative decrease and the presence of sand increases electrical resistivity. While, the presence of salt water and evaporation will greatly reduce electrical resistivity. From a statistical viewpoint, the data range is very large and represents less than one to more than 2000 ohm meters. But the abundance of points and depths with low electrical resistance (containing clay and saline water) is much higher than the high resistivity values ​​ (containing dry sand or floor rock). Several geo-electrical horizons can be identified in these sections and maps: 1. Horizons with electrical resistivity less than 10 ohms (saline water and fine-grained sediments); 2- Horizons with electrical resistivity of 10 to 20 ohms (clay with or without fresh water); 3. Horizon with electrical resistivity between 20 and 60 ohms (sand and coarse grained or freshwater sediments); 4. Horizon with electrical resistivity of more than 100 ohms (limestone, sandstone, volcanism). Based on the magnitude map of the entire magnetic field, the highest field strength for the investigated range is 50170 Nano-Tesla, the lowest intensity is 47118 Nano-Tesla field, and the average field intensity is 48213 Nano-Tesla, and the region is separable in two parts in terms of magnetization. Areas with relatively high to high field intensity and often include parts of the northwest, center of south and southwest of the study area. Also, in two areas due to coarse-grained sediments and high electrical resistivity, there is the possibility of underground water exchange with adjacent sedimentary environments.
4- Conclusion
The results showed that in two areas due to coarse-grained sediments and high electrical resistivity, there is the possibility of underground water transfer and exchange pathway. A geophysical disruption is proven by two methods of Geoelectric and magneto metric analysis in the lake.

کلیدواژه‌ها [English]

  • Quaternary
  • Sedimentology
  • Geoelectric
  • Geo-statistic
  • Urmia Lake