نوع مقاله : مقاله پژوهشی

نویسندگان

1 گروه زمین شناسی، دانشگاه بین المللی امام خمینی

2 رسوب شناسی و سنگ شناسی رسوبی، دانشگاه آزاد اسلامی، واحد تهران شمال

3 موسسه تحقیقات حفاظت خاک و آبخیزداری جهاد کشاورزی

چکیده

فرایند کارستی­شدن سنگ­های رسوبی از یک سو باعث بروز آسیب­ به پروژه­های راه و ساختمان، همچنین زمین­های کشاورزی می­شود، از سویی دیگر یک پتانسیل مهم برای منابع آب به حساب می­آید. منطقه الموت در زون ساختاری البرز میانی (مرکزی) قرارگرفته است و دربرگیرنده سازندهای دوران­های دیرینه­زیستی، میانه­زیستی، و نوزیستی است. مهمترین سازندهای کربناته الموت سازندهای سلطانیه، روته، الیکا، لار و تیزکوه می­باشند که در این میان گسترش سازندهای روته، الیکا و تیزکوه بیشتر از سازندهای سلطانیه و لار بوده و دارای اهمیت بیشتری نیز هستند. برپایه بررسی­های میدانی، پدیده­های کارست بیرونی و درونی در منطقه دیده ­شدند. بررسی­های سنجش از دور (RS) با بهره­گیری از GIS و نرم­افزار ILWIS بر روی تصاویر ماهوارهای لندست و مدل ارتفاع رقومی انجام گرفت. خطواره­های سازندهای کربناته منطقه از تصاویر ماهواره­ای و نقشه­های زمین­شناسی برداشت شد. این پژوهش نشان داد که میزان فشردگی خطواره­ها در سازند الیکا و روته نسبت به دیگر سازندهای منطقه بیشتر است. همچنین فشردگی شبکه آبراهه‌ها در سازند تیزکوه بیشتر از سازندهای الیکا و روته است که نشان از رابطه وارونه با تراوایی سازندها دارد. برپایه تلفیق بررسی­های توصیفی و داده­های کمی، به ترتیب و  از زیاد به کم: سازندهای الیکا، روته، تیزکوه، لار و سلطانیه دارای بیشترین شدت کارستی­شدن بوده ­اند.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

البرز میانی، الموت، انحلال، کارست، GIS

نویسندگان [English]

  • Parviz Ghazanfari 1
  • Mahdi Bakhtiari 2
  • Nader Jalali 3

1 Department of Geology, Imam Khomeini International University

2 Sedimentology and Sedimentary Petrology, Islamic Azad University, North Tehran Branch

3 Soil Protection and Watershed Research Institute, Agricultural Jihad

چکیده [English]

Processes of Karstification on the one hand cause problems in carrying out civil projects, and on the other hand it can help in the exploitation of water resources from hard formations and development of the geotourism industry. Karst landscapes are characterized by fluted and pitted rock surfaces, shafts, sinkholes, sinking streams, springs, subsurface drainage systems, and caves. The unique features and three-dimensional nature of karst landscapes are the result of a complex interplay between geology, climate, topography, hydrology, and biological factors over long time scales. Alamut Valley is located in north of Qazvin provenance and Central Alborz structural zone. Karst develops in many types of rock, including limestone, dolostone, gypsum, salt, and some others. These rocks, subjected to different climates, assume many morphologies and landforms. Limestone purity (%CaCO3) is one of the most important controls on karst development. Karst landforms develop best on pure, dense and thick limestones and marbles. The area of Alamut is 1866 Km2. Average rainfall in this area is more than 300 mm and average of temperature is under 13 OC. Carbonate rocks of Alamut are under highly dissolution because of climate condition and also high density of fractures. Rock units in this area include formations of Paleozoic, Mesozoic and Cenozoic Era. These formations consist of various clastic, carbonate and evaporite sedimentary rocks, as well as a variety of igneous rocks. The most important units of carbonate formations of Alamut are Soltanieh (Cambrian), Rute (Permian), Elika (Triassic), Lar (Jurassic) and Tizkuh (cretaceous). In karstification processes three parameters of lithology, climate and fracture are more important than others such as pedology, vegetation cover and topography. Among sedimentary rocks, salt rock has maximum dissolution rate. After that sulphate rocks such as gypsum, shows 10 times more Chemical Denudation than limestone. Limestone also has more dissolution rate compare it to dolostone (in comparison with dolostone, limestone is more soluable). Bedding planes and fractures (joints and faults) are of the greatest importance because they host and guide almost all parts of the underground solutional conduit networks that distinguish the karst system. The availability of water is the key climatic factor in karst development. It is certainly the principal variable controlling total denudation by dissolution.
 
Materials and methods
Investigation of remote sensing was performed by Landsat satellite images using ILWIS software to separate and calculate the area of carbonate formations, digital elevation model, distribution of carbonate formations, natural lineaments, slope directions as well as drainage map. Lineaments of carbonate formations extracted from satellite images and geological maps.
 
Results and discussion
The region is located in an area with two climatic regimes of Mediterranean rainfall (semihumid) and Siberian high pressure (cold-ultracold). Water is the main factor of karst development. The most important karstic landforms in the area are karren, dissolution pit, vug, cave and karstic springs. Varieties of karrens are microkarren, karren, runnel karren, rill karren, grike, rain pit. The caves of Alamut mostly identified in Ruteh Formation, for example: Sefidab cave in north of Sefidab village and Vali cave in near Gashnehrud. Angul cave in north of Dinak village also was formed in Elika Formation. The most important parameters casual Karstification of carbonate rocks in Alamut area are: purity, thickness, outcrop area and time of exposure of rock units, also rainfall, temperature and fracture intensity. Because of more rainfall and lower temperature, the north of Alamut valley shows more intensity of Karstification compare to south part of area. This research show more ratio of lineament intensity of Elika and Rute formations compare to others. The drainage intensity of Tizkuh is more than Elika and Ruteh formations (Table 1).
 
Conclusion
Based on the combination of all field works and remote sensing data, the intensity of karstification in the Alamut area from high to low, respectively are: Elika, Rute and Tizkuh, and also Lar and Soltanieh formations. Lar Formation shows maximum intensity of karstification in east of central Alborz zone, but in west of Alborz zone (Alamut) it has less intensity of karstification among all carbonate rock units. This difference is because of less thickness and outcrop of Lar Formation in study area.

کلیدواژه‌ها [English]

  • Alamut
  • Central Alborz
  • Dissolution
  • GIS
  • Karst