Lithofacies analysis and sedimentary link in sediments of Talkhab watershed (west of Ilam Province)

Document Type : مقالات پژوهشی

Author

• Yasaman Rafighdoust

Ferdowsi University of Mashhad

10.22067/sed.facies.v10i1.50125

Abstract

Introduction
Talkhab watershed is located in the southwestern parts of Iran, longitude 45 50 '00' 'and 46 00', and latitude 33 40 'and 33 48', and has two branches in the northwest (Chaman) and northeast (Srachamlu) that are joined together and form the main Talkhab river. The basin area is covered an area of 161 square kilometers and is elongated in shape. According to The geological division of the Zagros structural zone which is location in the Lurestan in SW Iran, this basin contains a relatively thick sequence of sedimentary rocks including Ilam, Gurpi, Pandeh, Asmari and Gachsaran formations. In this study, the Arc GIS software used to evaluate the geomorphology and physiography studies on order to evaluate the distribution of different geological units in this area. Therefore, the map shows that most geologic units are carbonate (Gurpi and Pabdeh) and evaporate rocks (Kalhor and Gachsaran) that are most abundant rocks in this region and they are very sensitive to erosion. The purpose of this study is to identify different lithofacies that form in this watershed and evaluate the sedimentary link toward downstream.
 
Method and Materials
In this study, 21 sediment samples from Srachamlu, 17 samples from Chaman and 32 samples from Talkhab Rivers have been collected for grain size analysis (coarser grains based on Lewis and McConchie, 1994; finer grains based on Coates and Hulse, 1985) in order to evaluate the finning to grain size toward downstream. Lithofacies were identified in the field based on Miall (2006). Textural parameters calculated based on Folk (1980).
 
Result and Discussion
The results indicate that grain size decreases toward downstream is not exponential and has discontinuities and isolated sedimentary links in Talkhab river. Based on the sedimentary analysis, four discontinuities and five continuities in sediments of the Sarcham, five discontinuities and six continuities in sediments of the Chaman and three discontinuities and four continuities of sediment in the main river of Talkhab have been detected. Our results show that hydraulic sorting has more effective role in downstream fining of the particle size in each of sedimentary links. Particle size parameters indicate that the studied sediments consist mainly of poorly to very poorly sorting grain size, positive skewness and flattened and elongated kurtosis. This indicates that discontinuities resulted from laterally input of coarse grain sediments from banks and tributaries (Marren et al., 2006; Simon and Rinaldi,, 2013), increasing the bed slope, exposed bedrock, changes in lithologic units along the stream bed and structural activities such as joints and faults. The lithofaceis recognized along the studied rivers consist of three coarse-grain gravely lithofaceis (Gmm, Gcm, Gmg) and one medium sandy lithofaceis (Sh). These lithofaceis have formed two architectural elements including gravity flow deposits (SG), gravel bars and bed forms (GB). Based on identified facies associations and architectural elements, the sedimentary model of Talkhab watershed is proposed as gravelly-bed braided river with sediment-gravity flow deposits in upstream and toward downstream shallow gravel-bed braided river system. Finally, we believe that this study can help in a better understanding of erosion and sediment yield patterns in such a basin for better water and soil preservation and watershed management.
 
Key word: Sedimentary link, Talkhab watershed, lithofacies, Ilam Province, finning downstream
 
References
Coates, G.F., & Hulse, C.A., 1985. A comparation of four methods of size analysis of fine grained  sediments. New Zealand Journal of Geology and Geophysics, 28: 329-380.
Folk, R.L., 1980.Petrology of Sedimentary Rocks. Hemphill Publishing, Austin, TX, 182 p.
Lewis, D.W., & McConchie, D., 1994. Analytical Sedimentology. Chapman & Hall, London, 197 p.
Marren, P.M., McCarthy, T.S., Tooth, S., Brandt, D., Stacey, G.G., Leong, A., & Spottiswoode, B., 2006. A comparison of mud and sand dominated meanders in a downstream coarsening reach of the mixed bedrock-alluvial Klip River, eastern Free State, South Africa. Sedimentary Geology, 190: 213- 26.
Miall, A.D., 2006. The Geology of Fluvial Deposits: Sedimentary Facies, Basin Analysis, and Petroleum Geology. Springer-Verlag, Berlin. 582 p.
Simon, A., & Rinaldi, M., 2013. Incised channels: disturbance, evolution and the role of excess transportcapacity and boundary materials in controlling channel response. In: Shroder, J., (ed.), Treatise on Fluvial Geomorphology. Elsevier, Amsterdam, 574–594 p.

Keywords

• Talkhab watershed
• lithofaceis
• architectural elements
• braided river

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