摘要
在西藏纳木错沿岸 ,发育了 6级湖岸阶地及拔湖 48～ 1 39.2m的高位湖相沉积。根据湖相沉积的U系法测年和孢粉分析结果 ,本文探讨了纳木错及邻区末次间冰期 (MIS 5)以来的古植被、古气候与湖面变化。研究表明 ,纳木错与邻区的湖面变化可以划分为 1 1 6～37kaB .P .间的古大湖———“羌塘东湖”期、37～ 30kaB .P .间的“古纳木错”外流湖 -残余古大湖期和 30kaB .P .以来的纳木错 -藏北湖群期等 3大阶段。在MIS 5的古大湖阶段 ,包括纳木错、色林错等藏北高原东南部的众多大、中型湖泊 ,是互相连通的一个大湖 ,其范围可能超过了现代的藏北内、外流 (怒江 )水系的分水岭。在MIS 5e末的最高湖面时期 ,湖面面积可达7880 0km2 ,它或许还与藏北高原西南部和中南部的其他古大湖相连 ,成为面积巨大的网格状深水大湖———“羌塘湖”。通过纳木错湖面变化曲线与西昆仑古里雅、格陵兰、南极等冰芯和深海岩芯的氧同位素变化曲线的对比可以发现 ,全球MIS 5的气温要高于末次冰期间冰阶(MIS 3) ,此时藏北高原为气候温和轻爽与湖面最高的大湖期 ;在末次冰期的两个冰阶 (MIS 4和MIS 2 )中 ,湖面明显下降 ,邻近的念青唐古拉山发育了小型山谷冰川 ;而在间冰阶MIS 3中 ,其气候波动的幅度 ,要比世界其他地区更加明显 。
Nam Co, located at the southeast part of the North Xizang (Tibetan) Plateau,is the biggest lake (1 920 km2) and the highest big lake (4 718 m a.s.l.) in Xizang. Leveling survey shows that there are 6 lake terraces and highstand lacustrine sediments from 48 m to 139.2 m above the lake level. Result of U-series dating of carbonate-bearing lacustrine sediments samples indicates that the highstand lacustrine sediments were deposited from 115.9±12.1 to 71.8±8.5kaB.P., the terraces of Nos.6, 5, 4, 3, 2 and 1 were formed in ca. 53.7±4.2kaB.P.?41.2±4.7～39.5± 3.0kaB.P.?36.1±2.2～35.2±3.0kaB.P.?32.3±4.4kaB.P.?28.2±2.8kaB.P.and 11.2±2.0kaB.P., respectively. Based on the data of U-series dating and sporo-pollen analysis, the paleovegetation, paleoclimate and lake-level variation of Nam Co and the adjacent regions since the Last Interglacial Stage (MIS 5) are discussed in this paper. Lake-level variation of Nam Co and the adjacent regions can be divided into the three stages: (1) The great paleo-lake of 116～37kaB.P., 'Lake East Qiangtang', (2) outflow lake between 37 and 30ka B.P., the 'Paleo-Nam Co' and the remnant great paleo-lake, and (3) Nam Co and North Xizang lakes since 30ka B.P. In the stage of great paleo-lake of MIS 5, a series of lakes, such as Nam Co, Siling Co and other big and moderate lakes in the southeast North Xizang Plateau were joined together into a great lake whose range might overstep the water divide between the North Xizang endorheic regions and the Nujiang River drainage. Especially in the stage of highest lake-level of late MIS 5e, the surface area of 'Lake East Qiangtang' may be achieved 78,800 km2, and its drainage area, 167,000 km2.It might be joined together with the other great paleo-lakes in the central-southern and the southwestern North Xizang Plateau, formed a giant net-shaped coalescent deep lake, 'Lake Qiangtang'. A comparison of the climatic change and lake-level variation from Nam Co with the data of Oxygen isotopic curve from the Guliya ice core in West Kunlun Mountains and that of the ice cores of GISP2, Greenland and Vostok, Antarctic shows that the temperature in MIS 5 was higher than that of the Last interstadial (MIS 3). During the MIS 5, the great paleo-lake stage, the climate in the southeast North Xizang Plateau was mild and slightly drier than that of the present. In the two stadials of Last Glaciation, MIS 4 and MIS 2, the lake level were obviously lowering and the small-size valley glaciation occurred in the Nyaiqentanglha Mountains. During the interstadial of MIS 3,the amplitudes of the climatic and lake-level variations in the region were higher than that of the other regions of the world, especially in period of 36～35ka B.P., the temperature and moisture were slightly or much higher than that of the present, but not the Holocene Climatic Optimum. In a word, the Asian Summer Monsoons on the Xizang Plateau in the periods of MIS 5 and MIS 3 were stronger than that of the present, especially in MIS 5e.
出处
《第四纪研究》
CAS
CSCD
北大核心
2003年第1期41-52,共12页
Quaternary Sciences
基金
中国地质调查局"西藏纳木错第四纪环境演变调查研究"(批准号 :DKD2 0 0 10 0 6)
1:2 50 0 0 0当雄幅地质调查 (批准号 :DKD990 10 0 1)资助项目
关键词
末次间冰期
西藏纳木错
晚第四纪
气候变迁
湖面变化
湖相沉积
Nam Co Lake in Xizang, Late Quaternary, climatic change, lake-level variation, giant paleo-lake:'Lake Qiangtang
