Ostracodes Assemblages and Their Environmental Significance from Lake Core of Nam Co, Tibetan Plateau
8.4 ka 以来纳木错湖芯介形类组合的环境变化意义

A 332-cm long lacustrine core was drilled in the middle south of Tibentan Plateau.From the core,15 species of ostracodes belonging to 6 genera have been identified.According to the changes of the ostracodes assemblage and the ostracodes ecological characters,which are sensitive to the changed of environment,three stages can be distinguished as follows:The early stage was from 8400 to 6800 aBP,during which the temperature descended in fluctuation which matched with the unstable cooling event of earlier Holocene,the climate was cold-humid,and the lake depth changed from shallow to deep.The middle stage was from 6400 to 2500 aBP,during which the climate changed from warm-humid to cold-humid and then became cold-dry,and the lake depth was becoming deep step by step.Weather pattern shifting during this period,from wet-cold to dry-cold,had been modifying and finally built up modern environments in Nam Co.The late stage(2500 aBP-present) showed a trait of lake depth increasing.At the earlier time of this stage,the climate was still cold-dry,which had the same trend of the end of the middle stage,however,the salinity of the lake increased;at the later time of this stage,the climate showed a general tendency toward cold-dry,as well as the hydrological condition of surface flowing water became faint.The concurrence of black shells percentage and the biggest ostracodes content,as well as the increasing of sedimentary hydrodynamic condition,indicated a post-mortem reworking.The abundance of Candona juvenile shells reflected juvenile mortality as a result of the rapid onset of unfavorable conditions such as catastrophic hydrological condition change.