Preliminary Study Of High-resolution Cyclostratigraphic Sequences Of Zhaojiashan Section Of Xiamaling Formation, Huailai County, Hebei Province

In this paper we present the results of cyclostratigraphic study of regular litological cycles in Xiamaling formation of Zhaojiashan section in Hebei Province, which is composed of balck shale, greyish-green shale, tan to reddish shale, greyish-white shale, siltstone to sandstone and marl, and show high-frequency variation of redox state of sedimentaion material. For this purpose, advancements of geochronological study of Meso-Neoproterozoic strata of the northern margin of North China craton and sedimentary environmental analysis of Xiamaling formation are presents firstly. Then, the theoritical basis, research advacement and possible problems of cyclostratigraphy are summarized, which benefits us in the study of Xiamaling Formation. The upper part of the third member and lower part of the fourth member of Xiamaling formation of the section was measured detailedly centimeter by centimeter, which was used for cyclostratigraphy study. Two methods was used here, ie. analysis of the hierarchical stacking pattern and spectral analysis of digitization of rock types time series.Simulative curve based on lithology and bed thickness is used for the presentation and construction of cycles. The terms of of couplet, bundle, bundleset are used here and the results shows that hierarchical rhythmicities have certain ratios which can be explained by the three Milakovitch cycles(eccentricity, obliquity and precession) of 1350Ma. So the elementary cycle in the section, which has a thickness of about 10 centimetre, may has a time span of 15000 year and can be regarded as sedimentary record of astronomical periodicity. However, it should be recognized that not every cycle has a very clear boundary, especially that of bundle and bundleset. Furthermore, spectral analysis of coded lithotype time series of the 0-918cm and 5311-6529cm part show main spectral peaks with wavelength ratios similar to those existing between the long eccentricity, short eccentricity, obliquity and precession cycles of 1350Ma.This allows us to propose a astronomical origin of the sedimentary cycles in Xiamaling Formation. Based on all data available, the Xiamaling formation in Zhaojiashan was estimated as a time span of 50Ma, Which may deposit from about 1400Ma to 1350Ma. Since the method of the hierarchical stacking pattern may not be perfect, it is choosing other proxy which is more reliable and having quantitative analysis of time sereise that should be focused in the future. Once the relationship between the sedimentary record and the orbital forcing is established, an unprecedented high time resolution becomes available.