Abstract: Caliche on gravel, as an indicator of variation of sedimentary environment, records relatively complete information on environment and climate. It usually appears as alternating bright and dark laminations, and its formation depends mainly on the purity of deposited carbonates, size of crystalloids, and foreign matters etc. This paper demonstrates that the shading image of caliche lamination can be obtained by using an ordinary scanner, and then the characteristic curve of the image can be automatically established by means of computer program. Furthermore, it can be compared with the characteristic curves of deep-sea oxygen isotope and loess-palaeosol sequence, and it can also be compared with grain-size and susceptibility curves of loess, as well as with tectonic events. In this way, the age of morphologic surface represented by the caliche can be estimated, while the effect of climate can be evaluated. A pilot study has indicated the feasibility of this method. It is indicated that this method not only may improve the precision and time-span of dating, but also leads to the applicability of sediment dating methods to the research of palaeo-environment and palaeo-climate. The following conclusions can be drawn from the present study: 1. The shading image dating of caliche micro-lamination widens the age range of ordinary dating methods; 2. The method may provide dating control for the research of palaeo-environment and palaeo-climate, and provides another evidence for the tectonic-climatic cycle; 3. The results of present study reveal that the relation between caliche thickness with time is not simply a constant accumulation relation; 4. As a record of successive sedimentation, caliche lamination is a valuable datable material. The major advantages of calliche dating lay on its simplicity, low-cost, abundant information and high accuracy. It is believed that with continued effort, the optimum resolution of this dating method can be improved to reach thousands or hundreds years. The application of this dating method to two sampling sites yields the following results: The age of T 11 terrace at Heishanxia Gorge of the Yellow River is dated to be 1 660ka B.P., and the age of the same terrace at Majiatan of Lingwu County is dated to be 1730～1780ka.B.P., which are in accord with the preexisting results. These results also support the feasibility of caliche dating method.

Key words: caliche micro-lamination, shading image, image scanning analysis, chronometry, climatic information

摘要： 砾石钙膜作为一种反映环境变化的沉积物标志,记录了比较完整的环境和气候信息,其实物的直接表现形式就是沉积了明暗相间的纹层,而形成明暗纹层的主要原因是受沉积时碳酸盐的纯度和结晶物的粒度以及杂质等的影响.作者用普通的扫描仪获取钙膜纹层明暗度图像,通过计算机自动识别获取明暗度变化的特征曲线,并将其与深海氧同位素曲线、黄土-古土壤序列、黄土粒度曲线、磁化率曲线等进行对比分析,从而达到确定砾石钙膜所代表的地貌面年龄的目的,同时分析其气候效应.初步研究表明,这种方法是可行的,它不仅提高了定年的精度和时间跨度,同时也拓宽了沉积物年代学方法在古环境及古气候研究中的应用.

关键词: 钙膜显微纹层, 明暗度, 扫描图像, 年代学, 气候信息