Environment And Climate Recorded By The Clay Minerals Of The Kuhai Lake Sediments In The Northeast Tibet Plateau Since The Last Deglaciation

A sediment core of 7.78 meters was obtained in the Kuhai Lake of the northeast of the Qinghai-Tibetan plateau. By using(AMS) 14 C dating method for the plant residues in the sediment core, the age model of the sediment core is established. According to the content of clay mineral, ratio and crystallinity index, chemical index and the combination of the granularity, deposition rate of sediment core, the change history of paleo-climatic and environment were studied in the Kuhai basin since the last deglaciation periods.By the content of clay minerals, illite crystallinity, chemical index and the ratio of clay mineral content, combined with the lithofacies, sediment grain size, sedimentary rate in high resolution(81samples, the sample interval is 8 cm, age interval is 310 years averagely), the basin experienced the following stages since the last deglaciation periods:Before 14.9 Cal ka BP,the high clay mineral content(60-66%)of illite, kaolinite /chlorite(0.65-0.95), kaolinite/illite(0.215-0.258)and kaolinite/smectite(3.9-5.4)ratio, low content(25-35%)of smectite, the smectite/illite(0.04-0.059) and smectite/(illite+ chlorite)(0.074-0.100), smectite/(illite+chlorite+kaolinite)(0.026- 0.034), chlorite/ illite(0.250-0.345)ratio,illite crystallinity index(0.167-0.196)and chemical index(0.310-0.345), showed dry and cold climate conditions. From 14.9 to 6.1 Cal ka BP, smectite content(2.5-12.8%),smectite/illite(0.055-0.235), smectite/(illite+chlorite)(0.105-0.390), smectite/(illite+chlorite+kaolinite)(0.035-0.150), chlorite/illite(0.285-0.420)ratio suddenly increased and low content(54.5-65.0%)of illite and chemical index(0.285-0.348)of characteristic, they indicated warm and humid climate conditions. But, this period was in terrupted in about 12.8 cal ka BP by a new dry and cold condition Younger Dry as event)for a short time. From 6.1 to 5.4 Cal ka B it was a transitional period from warm and humid climate conditions to cold and dry climate conditions. From 5.4 Cal ka BP to the present time it was a dry and cold climate conditions by the high content(59.3-66.0%)of illite, low content(2.4-8.2%)of smectite, the smectite /illite(0.038-0.140)and smectite/(illite+chlorite)(0.068-0.218), smectite/(illite+chlorite+kaolinite)(0.025-0.095)and chlorite/illite(0.255-0.420)clay and the deposition rate.With clay mineral comparation with pollen record of the same core, clay minerals like pollen can record paleoclimate and paleoenvironment changes. Both records have the general sequence of events along the core in the long time scale.