Reconstruction of Urmial Lake's Paleohydrology and Paleoecology in Quaternary By Studying Lake Terraces Biostratigraphy

During recent years, with the construction dam on main rivers, the occurrence of hydroecological drought during the last decades, and high evaporation of water reservoirs, the extent of the Urmia Lake has considerably decreased. Besides, salinity rate has increased to 650 milligram per liter. According to this hydrological situation organism cannot live in the Urmia Lakes. There is a lot of information about current chemical characteristics of Urmia Lake but we don’t have sufficient information about paleo hydrology and paleo salinity of the Lake especially in Quaternary. Investigation of The Urmia Paleo Lake terraces, their evolution and changes in elevations and changes in biostratigarphy characteristics are evidences for paleo environments of this lake. Dominant shell fragments of the Urmia Lake terraces are Gostropoda, Ostracoda, Foraminifera and Bivalves. In this study, type and spacious of shell fragments are investigated and the living environment situations of the organisms during formation of each lake terraces are determined. Using biostratigraphic study results and correlation between these environmental changes with elevation changes of lake terraces, Hydrological and ecological situations of The Urmia Lake during Quaternary was reconstructed. The results of biostratigraphy shows, in contrast to the current situation of water in the Urmia Lake (Hyper saline), most of the organisms lived in brackish and fresh water during formation of the lake terraces.