نوع مقاله : مقاله پژوهشی
نویسندگان
گروه زمین شناسی، دانشکده علوم، دانشگاه بیرجند، بیرجند، ایران
کلیدواژهها
موضوعات
عنوان مقاله English
نویسندگان English
1-Introduction
Rivers, as the most important factor in changing earth landscape, have been more effective than any other factor in shaping the human living environment. The understanding of the river processes and the factors controlling the behavior of rivers is important from different perspectives, including sedimentology. Examining textural characteristics, facies analysis and statistical indicators of river sediments, in addition to civil applications, can be a useful tool in the interpretation of ancient river sedimentary environments. In addition, the study of the behavior and nature of rivers and, accordingly, the study of watersheds from several aspects such as flood control, erosion and sedimentation have been of interest. The Afin River catchment is located in Southern Khorasan province and in the southeastern of Qayen. This river is the main source of agricultural water supply for villages located in this basin and has the greatest impact in terms of sediment production in the catchment area of Haji Abad Dam. The main purpose of this research is 1) to investigate sedimentological characteristics (textural parameters) and determine the effective factors in creating sedimentary discontinuities, and 2) to identify lithofacies and present a sedimentary model of the Afin River.
2-Materials and Methods
During the field study, 55 samples were taken from the channel bottom sediments by digging holes with a depth of 20 cm and with regular sampling intervals from the upstream to the downstream of the stream for grain measurement testing and the geographical location and height of each the sample was recorded by GPS. The active parts of the river channel have been selected for sampling. After sediment drying in the laboratory, the collected samples were analyzed using the dry sieve method with an accuracy of 0.02 grams. The results of the granulometry were drawn by Excel software in the form of histogram and cumulative curves, and the naming of the sediments was done according to Folk''s (1974) classification. Statistical parameters such as mean, median, skewness, and kurtosis were calculated for each of the samples using Folk''s comprehensive drawing method. In the field studies, the textural characteristics and sedimentary structures of the river channel wall sediments from upstream to downstream have been investigated and sedimentary facies have been separated based on Mial''s (2006) classification. In this study, the EPM model was used to calculate the annual erosion rate in the Afin River catchment.
3-Results and Discussion
Sedimentological studies of the Afin River show that several factors such as the entry of a large volume of coarse-grained sediments by sub-branches (inflow of lateral sediments), active tectonics, lithological changes and bedrock outcrops that cause to change textural parameters such as mean, median, standard deviation, skewness and kurtosis and have created an irregular grain finning trend from upstream to downstream. In the sediments of the Afin river channel wall, there are three clastic facies association (including the five gravelly facies Gcm, Gmm, Gt, Gh, Gp, the five sandy facies Sh, Sm, Sl, Sp, Sr and one mud facies Fm) and non-clastic pedogenic carbonates (P) have been identified, that based on them and other sedimentological features, five architectural elements such as SG, SB, CH, FF, GB have been separated. Two sedimentary facies models have been proposed for Afin River in the southeastern of Qayen. In the upstream part, this river is a gravel bed braided river with sediment gravity flow deposits, and in the middle and downstream part of the river, it is like a shallow gravel bed braided river.
4-Conclusion
The Afin River catchment with an area of 1181 square kilometers is located in the southeastern of Qayen city (Southern Khorasan province). In order to study of the finning trend of Afin river particles, 55 sediment samples from the main channel have been examined. The results of the granulometry analysis show that the finning trend of particles towards the downstream of the stream does not have a uniform trend and includes 6 sedimentary continuities and 5 sedimentary discontinuities. The arrival of coarse-grained sediments from tributary rivers, lithological changes, tectonic activities, and the appearance of bedrock are the most important factors in creating of these sedimentary discontinuities. Identification of the sedimentary lithofacies in the channel wall of the studied river was done based on textural features and sedimentary structures, which clastic facies associations (gravel, sand and clay) and non-clastic (pedogenic carbonates) are separated from each other. According to the sedimentary facies and architectural elements (CH, GB, SG, SB and FF) that are identified in the channel wall of the Afin River, two types of river channel styles proposed for the upstream to downstream sections of this river and the corresponding sedimentary facies model is provided.
Keywords: Sedimentary link, Southern Khorasan, Lithofacies, River channel style.
کلیدواژهها English
