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The CC1 core, with a length of 216 cm, was drilled in the west part of the Chen Co (Lake) in southern Tibet Plateau. The210Pb and137Cs measurement indicated that it was a consecutive sedimentary sequence since ca. 1400 years. The ostracoda and their assemblages under the level of 1 cm samples’ cutting interval were finished for this core to reveal the past environmental changes in the lake area. A total of 15 species of ostracods belonging to 7 genera in the core sediments had been identified. According to the ostracod distributions, abundances and preservations in the core, seven ostracod assemblages had been distinguished. The ostracod assemblages and their ecological features, together with the sediments dating decision were used to infer the past ca. 1400 years environmental changes of the Chen Co environmental evolutions in three stages, which had responded to the Medieval Ages Warm-period (MAW), the Little Ice Age (LIA) and modern warm period. The results show that the changes of the Chen Co environment had been mainly influenced by the climatic variations. The trend of the lake level fluctuations had been accorded with that of climatic variation during the past 1400 years.

Correlation fractal analysis and R/S analysis of four indexes from Core TS95, Tianshuihai Lake, western Tibetan Plateau, FeO, Fe 2O 3, the ratio of Fe 2O 3/FeO, and organic carbon, are conducted. It is found obviously that the 4 time series are chaotic and have Hurst phenomena. The chaotic or abnormal attractors for FeO, Fe 2O 3, Fe 2O 3/FeO and organic carbon are 2.8, 3.2, 2.9 and 2.5 respectively with saturated embedded dimensions ranging from 5 to 6, suggesting that the dynamic system controlling the local climatic and environmental evolution is chaotic. It has definte variables. To establish the system, at least 3 to 4 variables, at most 5-6 variables, are needed. This generally agrees with deep sea oxygen isotope and differs by large from some climatic indexes of loess profiles. The Hurst indexes of the four proxies are FeO 0.85, Fe 2O 3 0.76, Fe 2O 3/FeO 0.65 and organic carbon 0.74 respectively, indicating that they have obviously long run dependence persistence. This is in accordance with previous studies [13-15] . The persistence results most probably from the uplift of Tibetan Plateau. This suggests that in addition to the global vacillation of climate and environment, some local factors such as the uplift of Tibetan Plateau and the change in Tianshuihai Lake drain age, have probably played a role on the proxies of climate and environment. The differences between the four Hurst indexes result possibly from the relatively easy migration of FeO that is influenced by the hydrological change of the drainage. The organic carbon and Fe 2O 3, the two of the four, are probably more suitable to extract the persistence component of environmental evolution.

The “greatest lake period” means that the lakes are in the stage of their maximum areas. As the paleo lake shorelines are widely distributed in the lake basins on the Tibetan Plateau, the lake areas during the “greatest lake period” may be inferred by the last highest lake shorelines. They are several, even tens times larger than that at present. According to the analyses of tens of lakes on the Plateau, most dating data fell into the range of 40-25 ka BP, some lasted to 20 ka BP. It was corresponded to the stage 3 of marine isotope and interstitial of last glaciation. The occurrence of maximum areas of lakes marked the very humid period on the Plateau and was also related to the stronger summer monsoon during that period.