Abstract:

In this paper, based on the variation of major and trace elements of samples from the core-taking segment of the well BY1 in Biyang Depression by the method of portable fluorescence analyzer, all the tested elements above are sorted into four types of proxies for paleoclimate, paleoproductivity, paleoredox and paleosalinity. The results show that there is a good correspondence between the vertical change of geochemical elements and parasequence cycle changes, and the change of the geochemical element cycles can be also used for classification of more high-frequency sequences. During the process of lake-water depth changes from deep to shallow in a high-frequency sequence unit, varies of elements in shales show apparently regular change, especially on the high-frequency cycle interface, such as the gypsum and dolomite occur near the interface of saltwater and brackish environment respectively, in which the paleoproductivity decreases and the depositional environment transform gradually to oxidation. Those facts result in the organic matter content markedly decreasing near the top interface of high-frequency cycles. The change of geochemical element cycles provides a new effective method for dividing high-frequency stratigraphic unit and forecasting the heterogeneity of organic matter distribution.

Key words: mudstone and shale, geochemical element, stratigraphic high-frequency cycle, Hetaoyuan Formation, Biyang depression