شواهد ژئومورفولوژیکی تغییر اقلیم پلایای میقان در کواترنر

ماهیت بیشتر شکل ها و فرایندهای بیرونی زمین تابع شرایط اقلیمی حاکم بر یک منطقه در طول زمان است. بنابر این با مطالعه ژئومورفولوژیکی پدیده های مختلف محیطی می توان به بازسازی شرایط اقلیمی گذشته کمک شایانی نمود. تحقیق حاضر با هدف شناسایی شواهد ژئومورفولوژیک ناشی از تغییر اقلیم کواترنری در پلایای میقان به انجام رسیده است. بدین منظور ابتدا لایه های اطلاعاتی مورد نیاز تهیه و یا از تصاویر ماهواره ای irs p6 منطقه استخراج گردیدند و نقشه ژئومورفولوژی حوضه میقان بر مبنای آنها ترسیم شد. سپس محیط دیرینه پلایای میقان به کمک تحلیل چهار شاخص یخچالی، اقلیمی، انسانی و آزمایشگاهی برروی 11 نمونه رسوبی بازسازی گردید که نتایج حاصل از آن، بیانگر نقش فرآیندهای بادی و آبی در حمل رسوبات بود. همچنین ارتفاع 2400 متری مکان مناسبی برای تشکیل سیرک های یخچالی برآورد شد. در مجموع، در خصوص شرایط اقلیمی حاکم بر پلایای میقان در دوره های مرطوب کواترنری می توان ادعا نمود؛ بیشتر رسوبات عهد حاضر پلایا، متعلق به سنگ های آتشفشانی و شیل های حاشیه حوضه می باشند. همچنین با توجه به جورشدگی ضعیف نمونه ها، امواج در اکثر دوره ها فعالیت چندانی نداشته اند و رسوبات در محیط آرام مردابی تشکیل شده اند. وجود کانی ایلیت در اکثر نمونه های رسوبی، نشان از ابعاد بسیار بزرگتر دریاچه در گذشته دارد و مقادیر کمتر هماتیت در برخی نمونه ها حاکی از خروج رسوبات از آب، تحول اقلیم به سمت شرایط گرم و خشک امروزی و فراهم شدن شرایط اکسیداسیون رسوبات، طی زمان است.

Quaternary geomorphological evidence of Meyghan playa

AbstractThe nature of most of the external forms and processes of the earth depends on the climatic conditions prevailing over a region over time. Therefore, by studying the geomorphology of various environmental phenomena, it is possible to reconstruct the past climatic conditions. The purpose of this study was to identify the geomorphologic evidence of quaternary climate changes in Meyghan playa. To this end, the required information layers were prepared, or satellite images from IRS and ETM were extracted, and the Meyghan basin's geomorphology map was drawn up based on them. Then, the ancient Meyghan playground was reconstructed by analyzing four glacial, climatic, human and laboratory indicators on 11 sedimentary samples, the results of which illustrated the role of wind and water processes in sediment transport. Also, an elevation of 2400 meters was considered a good place for the formation of glacial circuses. In general, one can claim that the climatic conditions governing beige are in the Quaternary wet periods; most of the present sediments of the playa belong to volcanic rocks and shale margins of the basin. Also, due to the poor selection of samples, the waves did not have much activity in most of the courses, and sediments were formed in a slow melting environment.The existence of mineral Elite in most sedimentary samples indicates the much larger dimensions of the lake in the past, and lower amounts of hematite in some specimens indicate the deposition of sediments from the water, the evolution of the climate towards the present warm and dry conditions, and the conditions for the oxidation of sediments during Time is up.Keywords: climatology change, geomorphological evidence, Meyghan playa, quaternaryIntroductionPlayas from the past century have been of interest to geographers and geologists. The role of playas as a valuable evidence of climate change has been the main focus of this study. The aim of this study was to identify the geomorphologic evidence of quaternary climate change in Meyghan play. For this purpose, the necessary information layers were prepared, or from satellite images P6 IRS (with spatial resolution of 24 meters) were extracted and the geomorphology map of Meyghan basin was drawn based on them. Then the Meyghan playground was reconstructed in humid quaternary periods with the assistance of four glacial, climatic, human and laboratory indicators.The Meyghan sedimentary basin is 5528 square kilometers. Meyghan playa has 135 square kilometers area and is located at an average height of 1675 meters above sea level and at altitudes of Alborz and Zagros, 15 kilometers north and northeast of Arak city.Materials MethodsIn order to do this study, four glacial, climatic, and human and laboratory indicators were used as evidence assessment of wetter periods in Meyghan play. Then each of the indicators was identified and analyzed separately in Meyghan playa.Glacial Indices: For analysis of glacier indicators, digital elevation model, topographic map 1: 25000, satellite imagery IRS P6 and regional temperature map were collected. Then, by examining the shape of the curves of degree and conformance and their relationship with zerodegree line and satellite images, the circus placement was extracted from topographic map.Climate indexes: Regression relationship was established for calculating climatic indices, average temperature parameters and annual precipitation of 8 climatic stations in a 25year long period. From 1987 to 2012, the regression relationship was established and its equations applied on the digital elevation model of the area.Human Indicators: A review of human indicators through observation of the field and exploration of the studied area, or strategies such as testing on the evidence available in the playa environment to prove human life in playas in the distant period, is a strategic one.Laboratory Indices: For laboratory studies, data from 11 trenches we collected from the study area was used. In the first stage, field and survey operations were sampled in the study area. In each of the trench points, a trench was drilled to a depth of 75 cm with a small chisel and a shovel, which resulted in the removal of 11 samples of sediment from different locations with proper dispersion. Samples were taken in plastic and carefully labeled. Photos were then taken from the sedimentary environment of the samples. The laboratory parameters in this study included Granulometeric analyze, orthoscopic interpretation, and XRD and XRF tests. Discussion of Results Conclusions According to the Granulometry results of samples, calculating the chromobin index showed that samples 5, 6 and 7 were of river sediments and other samples were low sediment deposits. Most of the specimens also tended to finegrained particles. According to the analyzes, the present sediments of the present day are greater than the second and third Shale, containing chlorite and Elite minerals, as well as volcanic rocks (belonging to the Pliocene period) of the basin, and, of course, with moderate sedimentary maturity. The average temperature of the area during the quaternary period varied from a maximum of 2.67 to a minimum of 6.6 ° C. The results of morphoscopic analysis showed that in the transport of sediments to beech groves, in addition to the wind process, the blue process also played a significant role. Cumulative curves drawn on the basis of granulometric studies were also characterized by broken straight lines indicating that various mechanisms caused the sedimentation in the studied area. The analysis of the oxides of the main and secondary elements of the area showed; the origin of the deposits of the sediments of the area were of igneous rocks. From other points in the morphoscopy of sediments, it is found that kaolinite is found in the area of the plain, which goes underwater, and is much less visible on the margin of the playa, which proves the formation of kaolinite in the playground in Playa. Slowly Angularity of almost all quartz particles is evident in all samples, indicating the physical destruction of quartz during transportation to the desert and, of course, should not ignore the relative resistance of more quartz minerals.