青藏高原古里雅冰帽冰碛和冰水沉积物粒度特征及其意义

冰冻圈演化不仅与青藏高原水塔变化、地表侵蚀风化及荒漠化密切相关，还深刻影响着亚洲季风系统和全球气候，冰碛物的粒度组成可以为冰冻圈演化提供重要信息，但高原冰碛物的特征粒度组成及其形成机理仍不清楚，高原冰碛物与高原冷黄土及河湖沉积物的关系也不明确。为此，选择青藏高原最大的冰帽——古里雅冰帽的冰碛物及系列冰水沉积物，开展系统粒度组成研究。研究发现：自终碛到冰川前端冰水扇及下游河流冰水沉积均表现出特征的双峰模态，即1~3 Φ（500~125 μm）的中细砂峰和6~8 Φ（16~4 μm）的细粉砂峰，前者可能由冰川压碎、寒冻风化崩裂作用造成，后者由冰川研磨作用形成，并受到源区基岩岩性软弱和组成颗粒大小的影响。冰川磨蚀的细粉砂组分含量，从冰碛物经冰水扇、河流到湖滩沉积物整体呈现减小趋势，粗粉砂在湖滩沉积中几乎完全被风吹走，粗粉砂直接成为下游黄土的物源并富集其中成为黄土特征组分，水流分选在开口湖泊中产生粗、细粉砂的明显富集，这些证据揭示出，无论是与冰川发育相关的尾闾湖沉积还是近源、远源的青藏高原及周边黄土沉积，其粉砂组成和来源，均可为高原冰冻圈的形成演化提供重要信息。

Grain-size characteristics of tills and glaciofluvial deposits in the Guliya ice cap,Tibetan Plateau and its implication

The evolution of cryosphere in the Tibetan Plateau （TP）， which is closely related to the changes of water cycle， surface erosion， weathering and desertification， has exerted a profound influence on the Asian monsoon system and global climate. The grain size distribution of glacial deposits can provide important information on the formation and development of cryosphere in the TP. Up to date， however， the grain size composition and formation mechanism of moraines in the TP and their relationship with periglacial loess and fluviolacustrine sediments remain unclear. For this reason， a detailed grain-size analysis of the tills and glaciofluvial deposits in the Guliya ice cap， the largest ice cap on the TP， was carried out. It was found that the samples from the terminal moraine to the glacial outwash fan and a set of glaciofluvial deposits in the downstream rivers all show a characteristic bimodal size distribution， i.e. a 1~3 Φ medium-fine sand peak （500~125 μm） and a 6~8 Φ （16~4 μm） fine silt peak. The former may be produced by glacial crushing， frost weathering and breaking； the latter is mainly due to glacial abrasion. The lithology and grain size of the bedrocks in the source area exert also unignored influence. The contents of fine silt component of sediments from the moraine， outwash fan to the river beach generally show a decreasing trend. From the moraine， through glacial outwash fan， river to the lake beach at the entrance of the lake， the characteristic fine silt component of glacial abrasion shows a general decreasing trend. The lake dynamic sorting produces obvious enrichment of coarse and fine silts in the open lake， but they are almost completely blown away by the wind in the lake beach sediments， which directly become the dust source of the downstream loess and become the characteristic component of loess， The composition and source of silt， whether it is from the glacier-related tail lake deposits or from the near- or far-source loess deposits in the TP and its surrounding areas， can provide important information for revealing the formation and evolution of the plateau cryosphere.