普若岗日冰原西侧冰前风沙地貌的形成与我国冰川型沙漠的发现

在青藏高原中央、普若岗日冰原西侧流石坡地带山麓面上,分布有约100 km²的由戈壁与沙丘组成的地貌,这是世界罕见的、也是我国发现的首例中纬度、高海拔地区冰前沙漠沉积。野外地貌、地层测量和室内样品的粒度、矿物、¹⁴C测年分析等结果表明,其形成时代约为16 ka BP以来;沉积特征在沙丘沉积序列中表现为风成砂夹零星腐殖质层,在戈壁中表现为砾石表面具次生方解石或碳酸钙沉淀层;演化模式为冷直线式;形成条件为以下伏冰碛物为主要砂源,以行星西风环流和高原冬季风引起的地面西风为主要动力,以持续的寒冷半干旱为气候背景;成因主要与冰原西缘冰川作用形成丰富的冰碛物砂源有关;因此,这类沙漠与一般冰缘沙漠以河湖相砂为源具有显著区别,可称为"冰川型沙漠"。由于其形成兼与冰原、气候和环流的变化密切相关,所以它是高原腹地全新世气候环境变化的重要记录。

The Formation of Proglacial Desert on the West of Icefield Puruogangri and Discovery of Glacial-Type Desert in China

There are about 100 km\+2 of aeolian landforms consisting of gobi and sand dunes on the piedmont surface of rock stream slope at west side of Puruogangri icefield in the center of the Qinghai\|Tibet Plateau. This is one of the world s rare proglacial desert deposits and also the first example found in the mid\|latitude and high\|altitude region of China. Field observation, stratigraphic measurements, indoor sample analyses including particle size and minerals and \{\{\}\+\{14\}C\} dating showed that they had been formed since 16 ka BP. Some of the most striking depositional features are that scattered humus layers are intercalated in the sand dune sedimentary sequence; on the surface of gobi gravel there are secondary calcite or CaCO\-3 precipitates. The desert exhibited a cold rectilinear evolutional pattern. It was formed with underling glacial tills as the main sand source, with the planet westerly circulation and west winds caused by the plateau s winter monsoon as the main driving forces, and with persistent cold and semiarid weather as the climatic background. In other words their origin is related to the abundant sand supply from glacial tills at the west side of the ice field. Such desert is quite different from the periglacial desert with fluviolacustrine deposits as sand source and therefore is called glacial\|type desert. Since its origin is closely related to the changes of icefield, climate and atmospheric circulation, it provides important records of Holocene climate and environmental changes in the hinterland of the plateau.