Erosión y desertificación.-Land degradation of Taleghan drainage basin, Iran from saline and alkaline marly formations

Abstract

ABSTRACT In Iran fine – grained, saline, alkaline and erodible Tertiary marly formations are exposed in many geological zones and play important role in the formation of present landforms. They also play important role in degradation of water resources and soils as diffuse sources, they are the main sources of suspension loads of many rivers and are endless sources of sediments for sand dunes. These marly formations are present in Zagros, Central Iran, Alborz and Kopeh – Dagh Geological Zones and consists of different geological formations such as Gachsaran, Mishan and Razak Formations(in Zagros), Lower Red and Upper Red Formations(in Central Iran) and Neogene Red Beds(in Albors and Kopeh-Dagh). In this research, Neogene marly formations of Taleghan Drainage Basin, located in Alborz Geological Zone are investigated for chemical, physical and mechanical characteristics and erosion and sediment yield potential. The studied area is located about 100 kilometers west of Tehran and is one of the subdrainages of sefid-Rood Dam. Runoff and sediment yield were measured using field rainfall simulator. According to their physical and chemical characteristics, Neogens fine grained Formations of Taleghan Drainage Basin were classified into six subunits: Siltstone (NgSi), Claystone (gy1C), marl(gy1M), haliferous siltstone (NgSiH), haliferous claystone (gy2CH) and gypsiferous claystone (gy1CG). From the view point of salinity and alkalinity, NgSi unit is alkaline and NgsiH, gy2CH, gy1C and gy1CC units are saline and alkaline. The order of the units in respect to sediment and runoff production is as follows: NgsiH>Ngsi>gy2Ch>gy1CC > gy1C.