Late Quaternary Environmental Changes Of Lake Urmia Basin (Nw Iran) Inferred From Sedimentological And Magnetic Records

The ongoing changes affecting Lake Urmia (NW Iran) are revealed by the lake water level decrease (-7 m in the last 20 yr) that was attributed to natural and anthropogenic causes but the exact impact of these factors on the state of the lake is still not identified. Indeed, lack of detailed record of environmental evolution of the lake in the past limits the understanding of actual and future processes. Our project aims to obtain a high-temporal resolution record of environmental changes in the lake area for the last -30 kyrs. Sediment cores have been obtained from the recently dried out part of the lake near Urmia City, and surface and ground waters have been measured for electric conductivity. This paper presents results of water and sediments analyses. Six 14C AMS dating on organic fractions provide a chronological framework and indicate that the record covers the last -30 cal kyr BP. During this period, evaporitic conditions were prevailing in the lake. The electric conductivity of brines from the sediment highlights changes in the lake water salinity. The data indicate a lake-level low stand at -30 cal kyr BP that was followed by a water level rise and establishment of lacustrine conditions for the next -9 kyr, this phase representing the highest lake level recorded since that time to date. From the LGM, the lake experienced several fluctuations of the water level. The relatively long-term lacustrine condition established during the Early Holocene before the water level decrease between -5.5 and 4.9 cal kyr BP. Sediments from the two dry events at -30 cal kyr BP and at 5.5-4.9 cal kyr BP are characterized by the presence of greigite, which indicates anaerobic early diagenetic conditions in the sediment.