西藏安多剖面沉积物粒度特征及环境意义

对西藏安多剖面的3个层位沉积物与两个现代流动沙丘表层沉积物粒度组成、传统粒度参数及体积分维值进行了对比分析，探讨其粒度特征以及环境指示意义。结果表明：安多剖面的3层代表了3个不同的气候阶段，第一层（0～172 cm）沉积动力为风，其中在0.44～1.08 m深度处是一次风力加强的阶段，第二层（172～224 cm）、第三层（224～232 cm）均在6 Φ附近出现次峰，悬浮组分明显增加，推断为远距离输送的粉砂级颗粒沉降，表明这两个阶段风力有所减弱；安多剖面颗粒比研究区现代流动沙丘颗粒细，表明剖面可能为固定或半固定沙丘沉积；本研究区样品的体积分维值在0.215～1.77，虽然没有实际的物理意义，但作为粒度参数指标，在指示环境变化上是有效的，并且与粘粒、粉砂含量呈现明显的正相关关系，与细砂呈现明显的负相关关系。

Grain Size Characteristics and Its Environmental Significance of the Amdo Profile in Tibet,China

By analyzing the grain size component, traditional grain size parameters and volume fractal dimensions of three different layers of the Amdo profile in Tibet of China and two modern mobile sand dunes, the grain characteristics and environmental significance of the Amdo profile are discussed. The results showed that the three layers represent three different climatic phases. The first layer (0-172 cm) deposits of the Amdo profile are aeolian origin and the wind has strengthened at depth of 44-108 cm. Sediments grain size curves of the second layer (172-224 cm) and the third layers (224-232 cm) show that almost all samples have a second peak at 6 Φ, that means the increasing of the suspension component and a long distance transportation of silt particle sedimentation, indicating the weakening of wind force in this phases. Compared with the modern mobile sand dunes, all the samples from the Amdo profile are finer, which imply that the Amdo profile is likely to be a fixed dune or semi-fixed dune. Fractal dimension (D) of all the studied samples is 0.215-1.77, losing physical meaning in Euclidean 3D space, but the D value is still significant to indicate the environmental change. Volume fractal dimensions have a notable positive correlation with the content of clay and slit, negatively correlated with the content of fine sand.