摘要
在西藏自治区沉错湖泊三角洲平原和湖内钻孔取芯 ,利用14 C和ESR测年方法建立了钻孔剖面的年代标尺。在岩芯描述、沉积物粒度分析和CaCO3含量分析基础上 ,对沉错湖泊三角洲的沉积环境和沉积相进行了解释分析。 36 7m长的岩芯大致记录了 5 5万年以来的沉积历史。全孔平均沉积速率约为 0 6 6 7mm/a。 16 92 0aBP以来三角洲的沉积速率较大 ,平均为 1 2 7mm/a。由于沉积物物质来源的多源性导致CaCO3在剖面上的无规律性变化。但是 ,沉积物粒度和沉积序列变化指示全套沉积由底部的冲积扇相向上过渡为水下扇亚相和三角洲沉积相。在大约 175 0 0aBP～ 14 0 0 0aBP时期 ,沉错存在高湖面阶段。沉积序列中记录了末次冰期最盛期 (LastGlacialMaximum )和新仙女木事件 (YoungerDryas)。沉积特征和沉积环境的变化主要受湖面涨缩变化所控制。而湖面升降变化的驱动因素主要为气候 。
Chen Co lake is located at northern slope of the Himalayas. The geographical location of Chen Co lake is 28°53′～28°59′N,90°28′～90°35′E . The maximums of length and width are 11km and 7.8km respectively. The area of lake is about 37km 2. The maximum of depth is 31m. In lacustrine delta of Chen Co lake, 2 boreholes were drilled. In addition, using piston sampling method, 2.16m sedimentary core was gathered at 8m of the lake water depth. In laboratory, the time scale was established by 14C and ESR dating. On the basis of core description, grain size distribution, and CaCO 3 content analysis, the sedimentary environments and facies of lacustrine delta were explained. The 36.70m longer drilling core on the lacustrine delta plain recorded the sedimentary history since about 55000 aBP. The mean sedimentary rate of the whole borehole is about 0.667mm/a. Since 16920 aBP, the sedimentary rate rose and reached up to 1.27mm/a or so. The sediments of Chen Co delta indicate a complex of depositional processes. The main body of sediment consists of debris deposition of land-origin. The sedimentary strata sequence and sub-environment of deposition were recognized according to the colour, lithology, grain size, sedimentary structure, etc. Due to the multi-provenance of sediment material, the CaCO 3 content of lacustrine sediment showed ruleless change on profile. But, the grain size and sedimentary sequence indicated that the total sediment consisted of alluvial fan, subaquatic alluvial fan (fan delta) and delta sediment from bottom to upper. The sedimentary environment of delta also changed among delta front, delta plain and prodelta. Up to now, it presented the nature of delta plain environment. During 17500aBP～14000aBP, Chen Co lake witnessed the greatest lake period. In addition, the sedimentary sequence recorded the Last Glacial Maximum (LGM) and Younger Dryas cold event. The sedimentary characteristics and sedimentary environment were controlled by lake-level fluctuations.The authors suggested the driving factor of lake-level fluctuation is climate, especially the change of summer monsoon.
出处
《地理研究》
CSCD
北大核心
2004年第5期649-656,共8页
Geographical Research
基金
国家重点基础规划项目 (G19980 4 80 )
中科院知识创新项目 (KZCX3 SW 32 1)资助
关键词
沉错
三角洲
沉积环境
沉积相
湖面变化
Chen Co lake
lacustrine delta
sedimentary environments
sedimentary facies
lake-level fluctuation
