新疆巴里坤湖十五万年来古水文演化序列

THE PALEOHYDROLOGICAL EVOLUTION SEQUENCE OF BARKOL LAKE SINCE 150 000aB.P.

通过巴里坤湖钻孔岩芯沉积相分析、年代学测定、粒度分析、碳酸盐及其稳定同位素测定、孢粉分析等综合研究，建立了巴里坤湖沉积岩芯剖面十五万年来的时间序列、湖水位变化的古水文演化序列，分辨出十五万年来经历的高湖面阶段和低湖面阶段。低湖面阶段对应于冰期阶段，在冰期时，降水主要积累于山地，进入湖泊的水量较少，湖水位降低；高湖面阶段对应于间冰期的到来，山地冰川融化，湖水位迅速上升，但很快达到新的平衡，水位保持稳定。

Barkol Lake is located at the westem 15km of Barkol County in Xinjiang, it is one closed lake of the Barkol Basin. About 70m core was taken in l993～1994 for study this area environment evolution. This paper mainly study the paleohydrological evolution at the upper 25m core which is about 150 000aB.P. according to the age study and samples were taken by every 4cm.1 Depositional cycle and paleohydrology evolution The sediment in Barkol Lake were mainly the granule substance, such as clay,sand clay and clayey sand. The sediment charactenstic showed obviously cycles which can be divided into 9 different types sediment facies in this lake, they are: beach mudflat facies, limnal facies, shallow lacustrine facies(1), shallow lacustrine facies (2),shallow lacustrine facies(3), deep lacustrine facies(1), deep lacustrine facies(2), and deep lacustrine facies(3). In the core, the whole sediment cycles include 1 to 9 facies found in sometimes, they were changed from the deep lacustrine facies(3) at the lower tO the beach mudflat factes at the upside. But in majority condition, the depositional cycles were composed with 3 or 4 sediment factes. There are 30 cycles in the 0- 25.19m sediment bore and the factes study showed in generally that the sediment environment are changed from deep to shallow gradually and then become to deep abruptly. The other characterishc is that the cycle periods are short and the vibration ranges are little in the upside, but in the lower part, the cycle periods are long and the vibration ranges are large.2 Timescale Many age dating methods, such as Carbon-14 dating method, uranium series disequilibrium dating method, OSL dating and paleogeomagnetic dating method were used in the study for construct the timescale. Analysis the age data showed that the uranium series disequilibrium dating was more creditable than OSL dating in this study. And according to creditable age data, three paleogeomagnetic events were decided in the 25m core, they are Gothenburg, Lascham and Blake events. Combine the uranium series age data, the timescale are built, they area 12 000aB. P. in 2.24- 2.26m,18 000aB. P. in 3.58m, 42 000aB. P. in 9.93- 9.98m, 66 000aB. P. in the 13.86m,109 000aB.P. in the 17.82m, 128 000aB.P. in the 20.30~ 20.58m and 144 000aB.P. in the 25.01m.3 The paleohydrological evolution sequence of Barkol Lake since 150 000aB.P.Through the research to the depositional cycle, carbonate, oxygen and carbon isotope of the carbonate, and pollen analysis, we obtain such research results as: In the glacial period, the precipitation decrease, and the climate was dry and cold, the precipitation was accumulated in the mountain area as snow and glacier, the water capacity which inpour into the lake was decrement, the lake shrink. And in the begin stage of interglacial epoch, as the temperature rise, the snow and glacier which accumulated in the mountain area was melt, the water capacity which inpour into the lake become more, so that the water level raise. As a result of evaporation action strengthen evidently in arid area, the lake water was condensed, there were generous carbonate deposition, the value of δO and δC risen. But this condition became balance soon and the lake turned to calm evolution period. In the interglacial epoCh,the lake further shrink, evaporation action strengthen more, there were also more carbonate, even salt deposition.