内蒙古大青山水磨沟发现末次冰期冰川堆积物

Abstract

The current Quaternary glaciers in China only distribute on the high mountains surrounding the Tibetan Plateau in the west of 105°E. In the east of 105°E, glaciers only exist in Taibai Mountain, Changbai Mountain, and Snow Mountain and Yushan Mountain in Taiwan. Whether the Quaternary glaciation reached the lower elevation foothills and uplands in the east of 105°E is usually causing intense disputations among the researchers. This discovery of the glacier deposits in the Shuimogou areas of the Daqing Shan Mountain has provided confident evidence that the glaciers did cover the lower elevation hill ranges during the late Quaternary glaciation. Daqing Shan Mountain is located in the middle part of the Yinshan Mountain, Inner Mongolia. The highest peak is 2200 m above see-level. Remote sensing images indicate that there are two glacier eroded depressions within the Shuimogou valley. In the northern depression, the glacier deposits distribute around 500 m in NS direction and 400 m in EW direction and overlap the Proterozoic marble. The glacial deposits are mainly brownish red tillites composed with 60% sandy mud and 40% pebbles. There is no clear bedding within these morainic sediments. Pebbles have poor sorting, well rounding, and are cemented by mud and muddy sand. The major components of the pebbles are granite, gneiss, diabase, plagio-amphibolite. No underlying Proterozoic marble pebble has been found in the tillites, so the tillite components should experience long-distance transportation from their source regions. The pebbles have following characters:(1) the smooth pebble surface is coated with brownish red iron jacket;(2) the glacial striae on the pebble surface show random directions;(3) on all of outcrops, almost all pebbles with the size larger than 10 cm show the fractures of the strong extensional twisted shear deformation. The presence of intensive twisted pebbles distributing in the loose sediments indicates that the pebbles must be deformed during their transportation—glacier movement. During the outcrop creep of the glacier, the shearing force from the squirming of the ice tore the pebbles and created the pebble deformation. The tillites are covered by the landslides from nearby hill slopes and the flood deposits. A 0.5 cm thick of dark gray mud bed is interlayering within the middle of the flood deposits. The clays in the mud have been sampled for 14C-AMS age dating(DQS04-1). The age dating was performed in Beta laboratory. The 14 C age was corrected by 2? and the results are 13565 to 13440 cal a BP. This result indicates that the morainic debris deposited before 13.5 ka. These Daqing Shan tillites should form from the latest Quaternary glaciation. The identification of these glacier deposits proved the existence of Quaternary glacier in the foothill and highland area, east of the 105°E longitude around the 41°N latitude region. This discovery has significant importance for the study of geological history in this region and shines a light on the research of the climate evolution in East Asia and the Quaternary environment change in China.