东天山黑沟流域冰川沉积序列及OSL测年研究

OSL dating of glacial deposits and glaciations in the Heigou River valley,eastern Tianshan Range,China

黑沟源于东天山最大现代冰川作用中心博格达峰的南坡．在第四纪冰期与间冰期旋回中，该流域的冰川均发生过多次规模较大的进退，在谷中留下了较为完整的冰川沉积序列．这些冰川地形包含有重要的古气候变化信息，对其研究可重建黑沟流域的冰川演化史．应用OSL对该流域的冰川沉积物进行定年，测定结果表明冰水沉积物（沙质透镜体）比冰碛物更适宜应用单片再生剂量（SAR）测年技术进行测定．基于测得的年龄并结合地貌地层学原理可初步得出：晚第四纪期间，黑沟流域共发生了5次规模较大的冰川作用，分别为全新世期间的小冰期（16世纪以来冷期的冰进）与新冰期（距今3～4ka的冰进），末次冰期晚冰阶（MIS2）与早冰阶（MIS4）以及倒数第二次冰期（MIS6）．

The Heigou River originates on the southern slope of the Mount Bogda, the largest glaciated center in the eastern Tianshan Range. Ancient glaciers advanced and retreated dramatically during the glacial-interglacial cycles in Quaternary, the spectacular glacial depositional landforms were produced and well-preserved in the Hei- gou River valley, recording a complex history of Quaternary glacial cycles and landform evolution. These glacial landforms are a direct imprint of fluctuation of the ancient glaciers. Dating the glacial landform could determine the temporal and spatial variations of the ancient glaciers in this valley and also provide essential information for reconstructing the paleoenvironment in this region. Optically stimulated luminescence （OSL） dating technique was used to determine the ages of the fluvioglacial deposits （ the sand lenses that sandwiched between tills in mo- raines） and glacial tills in this valley with single aliquot regenerative-dose （SAR） protocol. Based on the dating results, and considered the principle of geomorphology and stratigraphy, the data of palaeoclimate as well as the glacial histories in the other valleys of the Tianshan Range, the following conclusion could be drawn： five glacial advances occurred in the Heigou River valley, they are glacial advances of Little Ice Age （ glacial advances in the cold periods since the 16th century） and Neoglaciation （glacial advances during the last 3 -4 ka） in Holocene, and other three glacial advances in the late and early period of last glaciation and penultimate glaciation, are e- quivalent in age to MIS 2, MIS 4 and MIS 6. In addition, the dating results of glacial tills and fluvioglacial de- posits show that the SAR protocol was appropriate for equivalent dose （De） determination of fluvioglacial depos- its and that OSL did not work to date glacial tills in this study, because the signals in quartz grains in glacial tills was not completely bleached. The glacial landforms indicate that the ancient glaciers at their maximum extensions during the LIA, Neoglaciation and the last glaciation were 7.6 km, 11 km and 14 km long, respectively.