RELATIONSHIP BETWEEN THE COLOR OF SURFACE SEDIMENTS AND PRECIPITATION IN ARID NORTHWEST CHINA

The relationship between the modern surface sediment color (e.g., L^*, a^* and b^*) and climatic parameters, including mean annual temperature (MAT) and mean annual precipitation (MAP), is the key to understand the past. Many studies on it are mainly focused on the modern soil and the paleosol-loess sediments in or around the Loess Plateau, and little have been devoted to the color of modern fluvial-lacustrine sediments and its relationship with climate. In this paper, we sampled at 57 sites along/around the Tianshan mountain region, very dry place in Xinjiang Area, Northwest China, to measure three parameters of color, the lightness L^*, the redness a^* and the yellowness b^*. The results show that the values of L^*, a^* and b^* are 67.0-80.0, 1.2-9.4 and 7.2-22.1 respectively. The relatively low correlation coefficient between L^* and a^* probably implicate little relationship between them, while the correlation coefficient between a^* and b^* is quite high. At the same time, the low correlation coefficient between altitude and either L^* or a^* probably imply that there is no relationship between the color parameters and MAT. However, the relatively higher correlation coefficient at different latitude means that color parameters are linked with MAP, The values of the coefficient can reach 0.28 and 0.37, 0.55 and 0.53 for L^* or a^* respectively. Further, we separate all color data into 16 groups in order to compare them with the precipitation records from the meteorological stations along/around the Tianshan region, the correlation index between the L^*, a^* and MAP are 0.44 and 0.55 respectively. We argue that such high ratios are results of the relationship between the precipitation and the surface sediments color, especially a^*. Additionally, due to too low correlation coefficient, we find no relationship between L^* and CaCO₃ (%) and the same situation may occur between a^* and hematite. In the future, we will measure the total organic matters and the rock magnetic parameters in order to make clear what are the coloring matters.