Aeolian sediments deposited in Lake Hamoun; the proxy of frequency and severity of dust storms in Sistan since the late glacial

Content Partner: Directory of Open Access Journals. Introduction Aeolian deposits are important palaeoclimate archives, partly because they are direct records of past atmospheric circulation (An et al. 2012). Distinguishing aeolian signature from lacustrine sediments is important for understanding the frequency and timing of palaeostorms. Efforts have been invested on deciphering aeolian records from lacustrine sediments in the United States (Dean 1997; Parris et al. 2010), Greenland (Mayewski et al. 2004), New Zealand )McGowan et al. 1996( and Japan )Xiao et al. 1997) providing a continuous record of Holocene aeolian activity. Sistan Basin is a remarkable environment to study Aeolian activity changes in eastern Iran – southwestern Afghanistan. The area is one of the driest regions in the world whose sparse water resources and fragile ecosystems are very sensitive to climate change. In moist periods, fluviolacustrine and palustrine conditions are dominant while in dry periods, aeolian activities prevail. Hence, variations of aeolian deposits in sedimentary successions could be a useful tool to evaluate palaeoenvironmental conditions over the Sistan Basin during the Holocene. Material & Methods The closed depression of Sistan, lying on the Iran-Afghanistan border, contains four shallow basins (mean water surface at about 471m asl) that receive the discharge of Hirmand River. Sistan is located whitin the Asian part of the desert belt of the temperate subtropical zone of northern hemisphere, with a semi-desert climate (Whitney 2007). In late spring, throughout summer and early autumn the Sistan basin is dominated by the northerly “wind of 120 days”. The winds are related to the north–south pressure gradient between a persistent cold high-pressure system over the high mountains of the Hindu Kush in northern Afghanistan and a summertime thermal low-pressure system common over the desert lands of eastern Iran and western Afghanistan as a result of sustained surface warming (Alizadeh-Choobari et al 2014). Two cores of H1 and H2 (6.2m and 6.8m long) were retrieved using a Cobra vibra-corer in west of Kuh-i Khawjeh in the dry lake bed Hamoun-e Hirmand in the Sistan Basin. Magnetic susceptibility (MS) determination (using a MS2C Bartington magnetic susceptibility meter), analyzing features of grain-size frequency curves (using a FRITSCH laser particle sizer) and petrography were conducted on sediment samples. A bulk sample was selected from the lower half of the c