بازشناسی تکامل دیرینه ژئومرفولوژیک کواترنری حوضۀ آبخیز گزازچای خلخال

نویسندگان

دانشگاه آزاد اسلامی واحد اردبیل

چکیده

حوضۀ آبخیز گزازچای به عنوان یکی از زیرحوضه­های رودخانۀ قزل­اوزن در ارتفاعات تالش شامل مجموعه­ای از نهشته­ها و لندفرم­های با ماهیت، سن و موقعیت­های متفاوت است. این حوضه بخشی از تاریخ طبیعی کواترنر ارتفاعات یاد شده را در خود جای داده است. بازشناسی این تاریخ و اشکال و لندفرم­های دیرینۀ شکل گرفته در بستر زمانی و مکانی آن هدف اصلی پژوهش حاضر را تشکیل می­دهد. این پژوهش از لحاظ روش از نوع بنیادی است که تجزیه و تحلیل آن بر پایۀ روش تحلیلی استوار بوده و طی آن عوامل و متغیرهایی مورد پژوهش قرار گرفته­اند که حداقل از کواترنر تا عصر حاضر به ویژه در طول هولوسن در شکل­زایی حوضه تاثیرگذار بوده­اند. تراس­های زمین­ساختی در طبقات متفاوت ارتفاعی، نهشته­های دریاچه­ای سدی هولوسن با تناوب دوره­های آب­وهوایی خشک و نیمه­خشک تا مرطوب، توالی عمودی نهشته­های رودخانه­ای در لابلای نهشته­های دریاچه­ای و نمود آن­ها به صورت یک سطح بازمانده،  نهشته­های پوششی و قرارگیری آن­ها بر روی نهشته­های دریاچه­ای و زمین­لغزش دیرینه مهم­ترین اشکال و لندفرم­های موروثی در سطح حوضه هستند. شکل­گیری این اشکال و لندفرم­های موروثی ارتباط مستقیمی با فرارفت سطح حوضه و فرونشست سطح اساس ناحیه­ای آن یعنی حوضۀ کاسپین جنوبی دارد. مهم­ترین تاثیر این فرارفت متروک ماندن تراس های زمین­ساختی به عنوان بخشی از سیسم گزازچای و اختلاف ارتفاع زیاد آن­ها با بستر کنونی رودخانه است. بدین ترتیب در طول تکوین حوضه برتری با فازهای کاوشی بوده است.
 

کلیدواژه‌ها


عنوان مقاله [English]

Recognition of Quaternary palaeogeomorphologic evolution of the Gizaz-Chay watershed Khalkhal

چکیده [English]

Introduction
   From the Quaternary period to the Neolithic age of the West Asian Region, which covers a wide range of Iran, it has undergone numerous environmental changes. In general, with respect to the natural history and environmental changes of the Quaternary region of the Middle East, which includes Iran and West-Asian, some researchers believe in the theory of cold and dry phases during glacial and warm and humid periods in interglacial periods. What is important to day and almost universally agreed is the coincidence of cold and dry weather-phase phases, with glacier conditions and wet phases, with the interglacial periods of the northern hemisphere. The Gizaz-chay watershed as one of the sub-watersheds of the Gezelozan River and one of the subsystems of the Baghrodagh mountains comprises a assemblage of deposits and landforms of varying nature, age and position in the landscape. This watershed is home to a part of quaternary's natural history that has embraced Tallesh Mountains. Recognition of this history and palaeolandforms formed in its temporal and spatial context was the main purpose of this study.        
 
Methodology
This research is empirical in terms of the method of analysis, which is based on the analytical method, in which factors and variables have been investigated which have influenced at least Quaternary up to the present time in the dynamics of the area surface. The physical instruments used include the topography map 1: 50000 and of geological map 1:100,000 kivi, aerial photographs 1: 550,000 satellite images taken from the Google Earth site. To determine the coordinates of identifiable forms and paleolandforms at the catchment area and transfer them to the map and the GIS environment, GPS has been used. In order to provide a chronological framework for reconstructing the history of long-term climate changes and evolution landscape of the basin during the Quaternary, the age-depth model presented for 13500 years of Neor lake (located 20 km north of the Gazakhshay Basin) Based on the core 7.5 meters from the southern lake peats.
 
Results and discussion
Although the Gizaz-chay watershed is presently from semi-arid and semi-humid weather conditions, the evidence of clay and brown silt layers in the lava cuttings of the temporary lagoon sediments belong to the Holocene, almost wet conditions It shows the present climate. Salt and clay-green clay layers with sandy interlayers can be interpreted as an index of colder and wetter conditions by reducing evaporation and higher lake levels. These layers represent a low-energy sedimentary environment with colder and humid climate conditions. Vertical sequence of river deposits along the lake deposits can be attributed to the lake recurrence due to dry and semiarid climate conditions, along with reduced rainfall and increased runoff energy. In such a situation, coarse sediments are transported to distant distances and are located on small-scale lake deposits.
 
Conclusion
The most important palaeogeomorphic evidence in the Ghizaz-chay Khalkhal basin is the following: Tectoinical terraces on different altitudes, lake sediments with the periods of dry and semi-arid to humid, Vertical sequence of river deposits along the lake's deposits and their appearance as a residual surface, covering deposits and their placement on the lake's deposits and the paleolandslide of the Neyakhoram.The lack of deposits with the origin of the large flood stream at the bottom of the dam, the gorge form of the Gazakhach River, as well as the large width of the natural dam consisting of trachytic volcanic rocks, suddenly disrupts is reject. The formation of these forms and heritages landforms has a direct link with uplift movements and subsidence Caspian Sea. The contining drop in regional base level as a result of subsidence of the Caspian Sea has driven incision and aide in the retention of the terrace deposits as they have been abandoned as the Ghizaz-chay systems have eroded downward. This way during evolution of the watershed has been predominance with erosive phase.

کلیدواژه‌ها [English]

  • Quaternary
  • Palaeogeomorphologic evolution
  • Gizaz-Chay Khalkhal Ghizaz-chay