波堆藏布谷地冰碛丘陵形成机制及其环境意义

Formation Mechanism of Hummocky Moraine in the Bodui Zangbo Valley and Its Environmental Significance

波堆藏布谷地中分布着大面积的冰碛丘陵, 通过考察发现其个体大小、外形、分布规模及内部砾石组成等方面都与高纬大冰盖外围形成的冰碛丘陵有很大的区别. 以冰川沉积学理论为基础, 从沉积动力学的角度讨论中低纬度波堆藏布谷地中冰碛丘陵的形成机制. 结果表明: 气候变化造成冰川的大面积死冰加之宽阔的河谷、海洋性冰川的特性促使波堆藏布谷中形成如此大面积的冰碛丘陵; 同时,大规模的冰碛丘陵表明气候转暖(抑或变干)的过程是突变的.

Late Quaternary Glaciations have been found in some U-shaped valleys located at Bomi County, SE China. Especially in the Bodui Zangbo valley, there are lots of hummocky moraines like tumulus. The hummocky moraines are 5~20 m high and 10~30 m wide and have high density near Lingqong about 30 km far form the existing glacier. The upper surfaces of the mounds are covered by lots of sub-rounded pebbles, showing that meltwater took part in the formation of the hummocky moraines. The insides of mounds are composed of angular granite blocks, and sometimes the internal sediments show a typical diamicton appearance with pebbles suspended in a coarse sandy matrix. The fabric and the shape of till give the evidence to prove the hummocky moraine was deposited in a stagnant ice condition and the blocks in the ice were merged out by different melt-out rate. So the mechanism of forming such a large hummocky moraine area is the combination with the large area of stagnant ice, flat base of valley and the special features of temperate glaciers. So large area of hummocky moraine suggests that glacier stagnation was more or less synchronous with climate amelioration (maybe, a temperature rising rapidly or a climate drying).