بررسی تحولات رسوبی و اقلیم دیرینه براساس رسوب شناسی و آنالیز عنصری در پلایای دامغان (مقاله علمی وزارت علوم)
درجه علمی: نشریه علمی (وزارت علوم)
آرشیو
چکیده
اقلیم شناسی دیرینه شامل مطالعه اقلیم در هر قسمتی از تاریخ زمین است که از این میان مطالعه تغییرات کواترنری و به ویژه هولوسن که ارتباط بیشتری با شرایط اقلیم کنونی زمین دارد. تغییرات محیطی و اقلیمی، سیگنال های ژئوشیمیایی را در رسوبات دریاچه ای به جای می گذارند که می-تواند در تفسیر شرایط محیطی و اکولوژیکی گذشته استفاده شود. پلایای دامغان واقع در مرکز چاله دامغان در استان سمنان واقع در نیمه شمالی کشور است. هدف از این پژوهش تحلیل تحولات اقلیم دیرینه در این پلایا با استفاده از داده های رسوبی، آنالیزهای دانه سنجی و آنالیز عنصری به روش ارزیابی شاخص های اقلیمی و تحلیل شرایط رسوبی و عناصر رسوبات است. براین اساس نتایج آنالیز های رسوبی و ژئوشیمیای در پلایای دامغان نشان می دهد در انتهای گمانه شرایط محیطی مرطوب بوده و با گذشت زمان در انتهای این دوره در این منطقه با روند تدریجی کاهش رطوبت مواجه بوده است. در رخساره بعدی شرایط اقلیمی شدیدا سرد و خشکی در منطقه حاکم می شود بعد از مشخص شدن این دوره سرد و خشک در انتهای این دوره شرایط گرم و مرطوب آب و هوایی در دامغان مسلط بوده است. در ابتدایگمانه نیز روند خشک شدگی دریاچه آغاز و بتدریج دریاچه ای شور و کم عمق در حوضه جایگزین می شود که نهایتا شرایط پلایایی در منطقه ایجاد شده و تا امروز ادامه دارد. نتایج نشان می دهند تفسیر ژئوشیمی (آنالیز عنصری ) نوسانات رطوبت، خشکی و دمای محیط را در توالی های مختلف در منطقه دامغان به خوبی مشخص می کند.Investigating sedimentary changes and paleoclimate based on sedimentology and elemental analysis in Damghan playa
Investigating sedimentary changes and paleoclimate based on sedimentology and elemental analysis in Damghan playaIntroductionPaleoclimatology includes the study of climate in every part of the earth's history, among which the study of Quaternary changes and especially the Holocene, which is more related to the current climate conditions of the earth, and in which human biological evidence is related to climate changes, is of particular importance. Environmental and climatic changes leave geochemical signals in lake sediments that can be used to interpret past environmental and ecological conditions.MethodologyIn order to reveal the changes of climatic conditions in the past and present, this research investigates the paleoclimate in this region through the evaluation of laboratory analyzes (granulometry, elemental analysis and its indices) on sedimentary data and the interpretation of paleoclimate conditions.The method of this research is a field, laboratory and analytical method in which by collecting data from the surface of the earth and then performing analysis, finally analyzing them and examining the influencing factors by integrating the results.The research data consists of library data and written sources, image data, sediment data collected during the field visit of the region and laboratory analysis.Results and Discussion In Core 1 of Damghan, there is a sedimentary type (silt, sandy silt, sandy mud) which indicates lake sediments and its shore because it is within the range of fine-grained sediments and does not include coarse-grained sediments. The type of sediment in core2 is also (silt, sandy silt, sandy mud), which sediments indicate sedimentation in a lake environment. The results of elemental analysis show that the amount of different indicators and elements in core 1 sediments is as follows, at the level of 10-12 13-11 at a depth between 156 and 100 cm, it indicates a cold and dry environment (low energy conditions). At level 9, at a depth of 80-100 cm, a small amount of moisture conditions and environmental energy increases. In the 8th level, the process of dryness and lack of humidity appears again, but in the 7th and 6th levels, there is an increase in humidity and a more humid environment than the previous environment. The fifth and fourth levels do not show a noticeable increase or decrease in humidity or coldness and heat. The third, second and first levels are the process of drying environment and the absence of moisture in indicators and elements, which are quite noticeable, which correspond to the conditions of the dry environment at the end of the Holocene. In core 2 Damghan, the elements and their indicators at the 10th and 9th level (150-170 cm deep) determine the transition conditions between cold and dry to hot and humid. In the 8th, 7th, and 6th levels, the depth of 90 to 150 cm sediments indicates wetter environmental conditions and erosion and environmental conditions are more.At the fifth level, there is a noticeable decrease in humidity conditions and an increase in the dryness of the environment. In the fourth and third levels, the general process is the same as before, but a very small increase in humidity is not observed. In the second and first levels, it shows the trend of dry and low humidity conditions, and the temperature of the environment has also increased, which corresponds to the conditions at the end of the Holocene.ConclusionTherefore, the results of sedimentary and geochemical analyzes in Damghan playa show that in the end part of core, the environmental conditions were humid and with the passage of time, at the end of this period, this area faced a gradual trend of decreasing humidity. In the next facies, extremely cold and dry climatic conditions will prevail in the region. At the beginning of core, the process of drying up of the lake begins and gradually a shallow and salty lake is replaced in the basin, which finally created flood conditions in the area and continues until today. The results show that the geochemical interpretation (elemental analysis) clearly defines the fluctuations of humidity, dryness and ambient temperature in different sequences in Damghan region. Also, granulometry and climatic indicators have been very useful in interpreting the sedimentary environment in Damghan region and it has clarified the ancient climatic conditions in this sedimentary environment.The results show that the geochemical interpretation (elemental analysis) clearly defines the fluctuations of humidity, dryness and ambient temperature in different sequences in Damghan region. Also, granulometry and climatic indicators have been very useful in interpreting the sedimentary environment in Damghan region and it has clarified the ancient climatic conditions in this sedimentary environment.
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