Characteristics Of Sedimentary Components And Its Environmental Information Of The Heihai,East Kunlun Mountains

Lacustrine sediments have the characteristics of continuous deposition,which can indicate environmental information of climate change.Study on Holocene environmental change by lake sediments in the Tibetan Plateau has become the international frontier research.Lakes in northern Qinghai-Tibet Plateau,because at high altitude and awful climate conditions,lake sediments in palaeoclimate research is relatively weak,especially the Heihai in the area of the East Kunlun Mountains.In this paper,we studied component characteristics of lacustrine sediments by XRD,ATEM,XRF,grain size analysis and Ostracoda analysis,combined with the AMS14C dating to discuss environmental information of the lake.XRD results show that clay minerals are illite(5%-35%)and chlorite(5%-30%),and average value of both minerals is about 20%which showing good positive correlation.Non clay minerals are quartz(average value is about 36%),plagioclase(average value is about 10%),and small amounts of orthoclase,hornblende,and pyrite appear occasionally.Salt minerals are small amounts of calcite,dolomite.Furthermore,small amounts of gypsum appear at 74-84 cm of the section,where carbonates have been disappeared.In section,the trends of Zr/Rb and Sr/Ba value are positively correlation,and had a significant inverse relationship with clay mineral content,high Zr/Rb and Sr/Ba value respectively indicates strong-intensity weathering and high-salinity of the lake,.The content of sulfur increased significantly at 74-84 cm,which is consistent with the gypsum and pyrite.A large number of plants remains appear at the same position.So,we can conclude that there is a sedimentary discontinuity at 74-84 cm of the section.Particle size analysis indicates sediments mainly come from transportation by water,and also a small amount provided by wind.The larger size of granularity in sediments also reflects the lake dwindled.A brief analysis of ostracoda indicates Heihai was a freshwater-brackish environment since the Holocene when it formed.Therefore,since 1972a.BP of the Holocene,we conclude the characteristics of regional climate in Heihai was cold and dry,which was mainly physical weathering,and with a weak chemical weathering.And during 1352 a.BP-352 a.BP,there was a sedimentary discontinuity resulting in the lake dwindled,which consistent with the extremely cold and dry event of the global and other areas in Qinghai-Tibet Plateau during the period of 1 ka BP,so it is confirmed that the climate of Qinghai-Tibet plateau was unstable,and there was extremely cold and dry event happened during the warmer Holocene in China.