关键词: 钙膜显微纹层, 明暗度, 扫描图像, 年代学, 气候信息

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