Sedimentary facies and downstream fining trend in Eshghabad-Suleh River sediments (SW Quchan)

The Eshghabad-Sule drainage basin with about 81. 365 Km2 is located in southwest of Quchan. The Eshghabad-Sule River is a gravel bar-bed river which its grain size decreased exponentially downstream. This may be related to selective transport of clasts on the streambed and abrasion during transport. To understand the grain size variations and effective factors in downstream fining، 34 samples have been analyzed. As results، 3 discontinuities and 4 sedimentary links were identified. In this basin، the role of hydraulic sorting in comparative with abrasion is more effective in downstream fining of grain size in each sedimentary link. Calculation of grain size parameters show that in this type of river، sediments are mostly poorly to very poorly sorted، positive skewed and platykurtic to leptokurtic. The identified lithofacies in this river are consist of matrix supported gravel (Gmm)، grain supported gravel (Gcm)، grain supported gravel with horizontal bedding (Gh)، sand with horizontal bedding (Sh)، laminated mud (Fl) and massive mud (Fm). Existing facies have formed in 4 architectural elements such as Channel (CH)، Gravity flow deposits (SG)، Gravel bars and Bed forms (GB) and Fine grain classtic deposits (FF). Based on identified facies associations and architectural elements، the sedimentary model of Eshghabad–Sule is gravelly braided river system.