Abstract by JunQing Yu oral presentation_15th East Eurasia International Workshop, Busan, Korea 2018

PRESENT RESPONSE OF QARHAN FLAT TO THE WATERSHED HYDROCLIMATE: THE KEY TO UNDERSTANDING PAST CONDITIONS FOR EVAPORITIC DEPOSIT FORMATION

JunQing Yu1,2*, Lisha Zhang1,2, Chunliang Gao1,2, Rongchang Hong1,3, Aiying Cheng1,2

1 Key Laboratory of Comprehensive and Highly Efficient Utilization of Salt Resources, Institute of Salt , Chinese Academy of Sciences, Xining 810008, 2 Qinghai Provincial Key Laboratory of Geology and Environment of Salt Lakes, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, China 3 University of Chinese Academy of Sciences, Beijing 100049, China Correspondence: [email protected]; Tel.: +86-971-630-7153

Qarhan Salt Flat is the largest deposit in China and covers an area of 5856 km2 of the in the nothern Tibet-Qinghai Plateau. Although efforts on the study of the evaporite deposit were tremendous in the past 60 years, answers to the following questions remained inconclusive: (1) the cause and commencement timing of the evaporitic deposition and (2) when and what resulted in the shift of evaporitic deposition to a playa environment. A deep paleo-lake prior to the evaporite deposit formation, as hypothesized by previous studies, is proven unlikely by increasing evidence from sedimentologic and geomorphic studies. Bieletan, the westernmost sub-playa of Qarhan today, did not belong to the uniform Qarhan Salt Flat until the beginning of the deposition of the top 20-m evaporitic sequence, based on both the configuration of evaporitic strata and the distribution pattern of the deposit. The present response of the salt flat to the watershed hydroclimate provides the key to the understanding of the past hydroclimatic and sedimentological conditions during the formation of the evaporitic sequence. One of the important findings of our work is the role of summer temperature in causing the formation of the uniform evaporitic deposition in the great saline lake of Qarhan. The top 20-m-thick evaporitic sequence is proposed to be formed in the early-to-mid Holocene because warmer climate resulted in the enhancement of precipitation in the high-altitude mountain catchment and the intensification of evaporation in the Qaidam Basin. Only in such circumstances the entire area of Qarhan Salt Flat could be inundated by increased catchment inflows and the consequent deposition of evaporites became possible. The timing regarding when the paleo-Qarhan saline lake became the playa environment is suggested to be from the late Holocene when the temperature decreased since then. Further investigation is required for establishing reliable chronological framework with efforts in overcoming difficulty in finding adequate dating material from the sedimentary sequence formed in the hyperarid environment. This research was funded by National Natural Science Foundation of China (NSFC-Qinghai Province joint grant No. U1407206; NSFC grant Nos. 41471013 and 41171171). Keywords: Qaidam Basin, Evaporitic deposition, Qarhan Playa, Fluvio-lacustrine observation, Watershed process