The sedimentary evolution of Da Qaidam Salt Lake in Qaidam Basin, northern Tibetan Plateau: implications for hydro-climate change and the formation of pinnoite deposit

摘要

Da Qaidam Salt Lake, northern Qaidam Basin, is known for its liquid and solid boron resource. More than that, pinnoite-bearing sediments, occurring in this lake, are rare in the world. However, little attention has been paid to the hydro-climate change and brine evolution correlation with the formation of pinnoite deposit. According to the multi-proxy records, as well as AMS C-14 dating, the sediment profiles DCD02 and DCD03 from Da Qaidam Salt Lake were studied. The results revealed that the ore-forming age of three pinnoite deposits are 7.83-8.62calka BP, 6.74-7.07calka BP and 4.66-5.41calka BP. The sedimentary evolution of Da Qaidam Salt Lake along with the pinnoite formation during the past 13,000years can be divided into four stages, i.e., (1) relatively fresh and deep paleo-lake with low salinity during 12.98-9.00calka BP; (2) seasonal variations between fresh and brackish paleo-lake during 9.00-8.62calka BP; (3) salt lake stage with relatively high salinity and alkalinity during 8.62-4.66calka BP, and (4) relatively shallow lake with high salinity since 4.66calka BP. Under favorable sedimentologic and hydrogeochemical conditions, a series of boron deposits including pinnoite ore formed in different zones of Da Qaidam Salt Lake due to the different ore-forming mechanisms. Finally, under the differential effect of climate warming condition between the high mountain catchments and arid basin, the boron ore-forming model was established as a higher mountain-lower basin-shallower water model.