Holocene hydrological changes in SE Iran, a key region between Indian Summer Monsoon and Mediterranean winter precipitation zones, as revealed from a lacustrine sequence from Lake Hamoun

Abstract

Core sediments from the dry lake bed of Hamoun were subdivided into 3 main sedimentary units using a multi-proxy approach (e.g. petrography, grain size analysis, total organic matter % and CaCO3% determination) to reconstruct the palaeoenvironment of the Sistan Basin (SE Iran) as a transition zone between the monsoon summer precipitation zone of south Asia and the Mediterranean winter precipitation zone of the Iranian plateau during the Holocene. Data revealed that during the late-glacial to early Holocene, the lake and its catchment area, western Hindu Kush, were under a more prominent influence of the Indian Ocean monsoon and formed a moist and productive environment with less wind action, as shown by the provenance of high organic matter lacustrine sediments together with the lack of an aeolian fraction. Due to southward migration of the Inter Tropical Convergence Zone during the mid Holocene, arid climate manifested by an interplay of seasonal aeolian and fluvial deposition became dominant. These conditions were due to reinforcement of subtropical anticyclones on the Iranian plateau. The presence of green to brownish green moderate organic matter lacustrine sediments showed that during the late Holocene, Mediterranean-type winter precipitation dominated in the area. During the initial part of this period, the Shahr-i Sukhteh civilization was close to the lake. The environment was relatively similar with that of today. Some palaeostorms can also be detected during this time interval, shown by occurrences of high aeolian inputs in the basin.