مشخصات پژوهش

صفحه نخست /A sedimentary model of ...
عنوان
A sedimentary model of mountainous rivers with application to Alamutrud and Shahrud rivers, N Qazvin, Iran
نوع پژوهش مقاله چاپ‌شده
کلیدواژه‌ها
Fluvial sedimentology . Suspended load . Bed load . Depositional model . Central Alborz
چکیده
The most important depositional processes in continental sedimentary basins occur in fluvial systems. In this study, sedimentology of Shahrud River and its eastern tributary (Alamutrud River, N Iran) was studied for the first time. The study area is located in the Southern-Central Alborz structural zone which is mostly composed of Eocene volcanics and Miocene terrigenous sedimentary rocks. The channel trend is controlled by the regional structural trends. Grain size analysis was performed on 110 sediment samples. Water discharge and velocity was measured on 274 points of the river cross section. A total of 182 bedload and suspended load sampling were also performed in 9 hydrometric gauging stations. The results show > 70% of the bedload and suspended load consist of sand and silt, respectively. Mineralogic composition of gravel, sand, and mud fraction of the sediments indicates a dominant volcanic origin. Two gravelly facies (Gmm, Gcm), five sand facies (Sm, Sh, St, Sp, Sl), and one mud facies (Fm) were recognized. These facies have been formed by six architectural elements: channel (CH), gravity flow deposits (SG), gravel bars and bed forms (GB), sand bed form (SB), laminated sand sheet (LS), and fine grain overbank deposits (FF). Accordingly, the system is influenced by flood and the depositional model for its upstream is proposed as gravel-bar braided with sediment-gravity flow. The river in midstream and downstream shows characters of shallow gravel-bed braided and gravelly-sandy meandering rivers, respectively. Coarse-grained sediments feeding by the channel tributaries and alluvial fans have produced distinct discontinuities in the downstream fining trend.
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