Journal of Stratigraphy and Sedimentology Researches (Mar 2017)

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

  • Mohammad Ali Hamzeh,
  • Mohammad Hosein Mahmudy Gharaie,
  • Hamid Alizadeh Lahijani,
  • Reza Moussavi Harami,
  • Morteza jamali

Journal volume & issue
Vol. 33, no. 1
pp. 1 – 24


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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 core H1 for radiocarbon dating. The calibrated date suggests late-glacial age for lower parts of the core H1 (13.5 ka). Discussion of Results & Conclusions The core lithology generally consists of clayey silt, silt and sandy silt layers. Based on basic sedimentological data, MS and sediment color we have recognized three main facies, A (lateglacial - early Holocene), B (early- mid Holocene) and C (late Holocene). Since the late-glacial, the climatic regime of interior west Asia has been under the influence of various atmospheric circulation patterns and intensities (Fleitmann et al. 2007). High pressure cells of the Siberian Anti-cyclone (Siberian High: SH) from the north, low pressure cells belonging to the Indian summer monsoon (ISM) from the south, and mid latitude westerlies (MLW) governed the regional climate during thid period. Data revealed that during the lateglacial - early Holocene, dominance of low pressure system of ISM on Sistan Basin and the western Hindu Kush provided a moist environment with less wind action. As shown by primary modal peak of grain-size distribution curves (20-30 µm), massive clayey silts with low MS (4.2 - 5.2 ×10-4 SI) and abundant plant remains, charophytes and carbonate shells in facies A are deposited in a highly productive lake with no signs of wind action. This period is also characterized by weakening MLW as well as elevated sea surface temperature in Atlantic Ocean and Arabian Sea. In addition, this humid period in the Sistan Basin is concurrent with the early Holocene long-term weakening of SH, inferred from increases in concentration of K+‏ in GISP2 ice core (Mayewski et al. 2004) causing dramatic decrease in north-south pressure gradient between the Hindu Kush Mountains in northern Afghanistan and the desert lands of the Sistan Basin. High solar irradiance and weakening and northward migration of territory influenced by the SH also pushed the ISM domain northward (Mayewski et al. 2004) affecting Sistan catchment basin. During the early- mid Holocene gradual weakening ISM (Sirocko et al. 1993) in addition to strengthening SH and MLW (Bradbury et al. 1993) caused dominance of severe wind storms in Sistan, as shown by modal peak more than 100 µm in facies B. During the mid-late Holocene, episodic high aeolian inputs in the basin by high energy dust storms comparable with the present day “winds of 120 days” are evident. Traces of palaeostorms during this time is evidenced by high oscillations of MS and presence of some sand-bearing lacustrine sequences in both cores. During this period, southward migration of ITCZ led to weakening of the ISM (Fleitmann et al. 2007), and consequently drought periods in Sistan Basin and semi-arid conditions over NW Himalaya (Dortch et al. 2013). Establishment of a high pressure gradient between the Sistan depression and the high Hindu Kush Mountains caused the occurrence of severe and frequent dust storms over the area. Our results suggest that the late Holocene in the Sistan Basin (facies C3) was characterized by frequent changes in MLW and SH activity. Palaeoclimatic records show since the mid Holocene to the present time, the climate of Sistan and its catchment area more or less oscillated around a steady state comparable with modern situations (Hamzeh et al. 2016). During this time, the hydroclimatic regime and Aeolian activity of the Sistan Basin and NW Himalaya have been mostly governed by MLW-associated precipitation. Periods of prolonged droughts are indicated in proxy records of NW Iran such Lake Neor (Sharifi et al. 2015), presumably consistent with high MS values in our record. It is possible that weakening of ISM, along with distal influences of the MLW during the late Holocene exposed the Lake Hamoun basin to frequent droughts. Frequent lake level fluctuations show unstable climate of the Sistan Basin during mid to late Holocene with frequent wind storms.