نوع مقاله : مقاله پژوهشی
نویسندگان
دانشگاه تبریز
چکیده
دشت تبریز، که بخش مهمی از آذربایجان شرقی است، در طول تاریخ تغییرات اقلیمی مهمی را پشت سر گذاشته و پس‌روی و پیش‌روی توده‌های آبی مهم، مانند دریاچه ارومیه، بر سطح آن رخ داده است. شواهدی از این تغییرات اقلیمی و پس‌روی و پیش‌روی توده‌های آبی در سطوح دشت بر جای مانده است که می‌توان بخشی از این شواهد را در رسوبات دشت تبریز پیگیری کرد. در این مقاله، برای پاسخ به سؤالات طرح‌شده در زمینه نوع و نحوه تغییرات گذشته، سعی شده است در محدوده‌های مشخص، که داده‌هایی از ویژگی‌های فیزیکی و شیمیایی سازندها قابل دسترس بوده‌اند و بر اساس این داده‌ها لایه‌ها قابل تفسیرند و از نظر ژئوکرونولوژی اهمیت زیادی دارند، چینه‌ها و لایه‌ها بررسی شوند. همچنین در مواردی برخی ویژگی‌های لایه‌ها مورد آزمایش خاک قرار گرفتند. در این تحقیق، از داده‌های سازمان قطار شهری بهره‌گیری شد و از متخصصان مربوطه اطلاعات لازم به دست آمد. همچنین سعی شد با حضور در محدوده‌هایی که حفاری‌ها و گودبرداری‌ها صورت گرفته همه لایه‌ها از نزدیک مورد بازدید میدانی قرار گیرند و در موارد لازم اندازه‌گیری‌ها در محل صورت گیرد. برای رسیدن به هدف، از نتایج آزمایش‌های SPT، روش‌های پالئوپدولوژی، و نتایج آزمایش دانه‌بندی و ph استفاده شد. نتایج بررسی‌ها نشان داد در بخش‌های مهمی از دشت تبریز عمق 5/2 تا 10 متری عموماً از لایه‌های متشکل از رس سیلت‌دار سفت تا بسیار سفت همراه یک لایه شن رس‌دار و عمق 10 تا 5/18 متری از لایه‌ها متشکل از ماسه سیلت/ رس‌دار بسیار متراکم تشکیل شده است. در بعضی از قسمت‌های دشت نیز ماسه‌های بادی دیده می‌شود که از حاکمیت شرایط خشک در محدوده دشت حکایت می‌کند. بررسی دانه‌بندی لایه‌ها نشان می‌دهد دشت تبریز دوره‌هایی را با شرایط اقلیمی مرطوب تا خشک پشت سر گذاشته است. گسترش دریاچه ارومیه تراس‌هایی را در این دشت بر جای گذاشته که خود از وقوع تغییرات اقلیمی مهم در محدوده دشت تبریز حکایت می‌کند.
کلیدواژه‌ها
موضوعات
عنوان مقاله [English]
Monitoring of environmental changes of Tabriz plain at Quaternary sediments
نویسندگان [English]
- Maryam Bayati Khatibi
- Fariba Karmi
- Behrouz Sari Saraf
Tabriz University
چکیده [English]
Abstract
Sediments provide a continuous, sensitive record of changing conditions of environment and processes within plain and in the surrounding plain, thus they contain significant archives of past environmental change on the continents. Valuable informations on regional and global scale patterns of past climate
variability in the Azarbayjan region have been documented by numerous paleoclimate studies, but some of these may partly explain the contradictory palaeoclimate histories. Although paleoclimate changes in the eastern Azarbayjan during the late Pleistocene to Holocene are well constrained in terms of proxy-climate data. In this study the data were collected, the sub-bottom profilers. In this study with aim of monitoring of past environmental changing of Tabriz plain, widely used indicators of Quaternary paleoclimates. In particular, the geochemical ”archives” contained in sediments provide long and high-resolution proxies of terrestrial records. However, such geochemical proxies especially those gathered from the holes , can only be indirect indicators of past climates and may be influenced, to different degrees, by several independent factors. In order to overcome this indirectness, multi-proxy methods are widely used. Spt methods ,Granolometry,and textural methods are these used method. Also used Ph analyzing for explain of Quaternary history of Tabriz plain. The result of this study suggested of the Tabriz plain hade very different paleoclimate conditions. The amount of clay and soft grain sediment in depth of ground is high. Our results indicate that the region was relatively cold and wet during the late glacial, and some times were dry. During the beginning of the Holocene, while precipitation values were high, the temperature gradually increased than , the region was warm but extremely dry.
1-Introdution
Sediments are sensitive to climatic (global and local)and tectonic, and sedimentological changes,providing clear sedimentary records about them. Shore deposits are generally composed of loose, unconsolidated sediments, ranging from very fine sand up to pebbles and cobbles in terms of sediment size. They receive their sediments from rivers draining a catchment area and the erosion of nearby cliffs and foreshore outcrops. fluvial sediment capacity transported to the coastal area. Shore systems deal with the nteractions between depositional and erosional processes as waves, currents, rivers, tides, and winds). The Tabriz plain undergone significant modification associated with water level changes related to climatic conditions and tectonism since its formation
The East Azarbayjan plain is situated on basement rocks consisting of Mesozoic metamorphic rocks,
Triassic limestones, Upper Cretaceous ophiolites, and Miocene turbidites. These rocks are unconformably overlain by Quaternary volcanics and coeval lacustrine sediments. The basin infilling ends with Late Quaternary travertines and recent unconsolidated fluvial sediments. To restructure the past climate and environmental conditions is crucial in terms of understanding the living conditions of previous communities. On the other hand, the accurate interpretation of human impact on past environmental conditions is very important in terms of fully understanding the dimensions of man's pressure on nature and the changes in land use. Human impact emerges as an important and constant factor that regulates the vegetation dynamics in the lands occupied especially in the Late Holocene. In general, the climatic changes experienced in the Eastern Azarbayjan region and Tabriz plain are consistent with the hole layer data. This is impoErtant in terms of reflecting effects of global
climatic changes in the study area.
2-Materials and methods.
To restructure the past climate and environmental conditions in the Eastern Ayjan region in the Late Pleistocene and Holocene investigated by grianology analysis. In this study ,used of Geocronology data ,sediment layer and pedology property for experting of environmental changes in Tabriz plain. In field study is measured and is analysed grain of sediment in laboratory. Also used spt method for investigation on soft grains in sediment. Investigation on PH of sediment and deposits were other methods for understanding of past environment condition.
3-Results and discussion
Extensive paleoclimatic studies have provided evidence that the Holocene is characterized by wet and dry climatic fluctuations and rapid shifts worldwide. We propose that, the sedimentary record of Tabriz plain
provides a suitable geological archive for understanding the changes in this climate sensitive coastal area. The work reported here is predominantly focused on lithological observations, inorganic parameters and basic organic matter characteristics. The field work were collected from of the sediment cores. The latter technique has been used to obtain geochemical profiles, which are interpreted to identify local climate signals, distinguish internal and external effects on the environment such as physical dynamics, chemical
characteristics of the soil column. This study also aims to analyse the effect of main global climate trends on the environment of plain such as the Early Holocene humid phase, the Middle Holocene dry conditions and various Late Holocene events including organic matter rich sedimentation. Investigation on sediment layer show that from 15 to 35 meter is formed by clay ,sandy –silt and silt. This composition is suggested of low energy in past environment. Changes of sediment property is show that climate changed. Investigation on soil sampels and analysied by spt method show that most of grains is soft in deep of layers. In between of layer can see wind sands. Percent of Clay grain is decrease in eastern part of plain.
4-Conclusion ,Keywords
The study of distribution of soft grain materials in Tabriz plain show that most part of area in 20 meter of deep is formed by soft grains. 50 percent of this soft grains are clay and silt. Northern part of plain is formed by red soils that sources of his soil is Quaternary sediment. Thick layer of clay suggested of dry condition continued length time . Yellow soil is evidence of cold and dry condition in Tabriz plain. Old landslides in between layer show that in plain wet condition some time were governed. Especially the signal of the Early Holocene humidity is documented in sedimentary record. Such investigations which are now in progress will provide further insight into climate-induced changes in the sediment.
Thick of wind sand layer suggested that the warm period is governed 400 year in plain. This period marked by color layer in around of Tabriz.
کلیدواژه‌ها [English]
- Environmental changes
- climatic changes
- Tabriz plain
- Sediment
- Quaternary
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