某地区白垩系中的冲积相
STUDY OF CRETACEOUS FLUVIAL DEPOSITS IN A CERTAIN DISTRICT
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摘要: 整个白垩系为砂泥岩互层,M段、W段、L段下部及D段下部为砂岩及砂砾岩。前人对W段及L段曾提出湖相及河湖交替相的看法。遵照毛主席关于“实践、认识、再实践、再认识”的教导,我们对W段和L段进行了研究,确定其为冲积相。本文是对该二段冲积相特征的讨论。Abstract: This paper describes the characters of Cretaceous Red beds such as: the size distribution, sedimentary texture, paleocurrent, characteristics of lithofacies, structures of facies-profile of the fluvial deposits of W and L members. The types of W- and L-paleostreams are analysed and the nature of some of the paleostreams are discussed.The range of the clastic composition of sandstone, M-W-L-D members from the lower part to the upper part of the section may be related with the vertical succession of strata of the oldland.Particle-size statistics, CM pattern, diagram of Sk1-σ1, αs-Sos, α3-σ, current-bedding and the succession of beddings evidently illustrate a fluviatil origin, for these deposits.Grand means (θ) and standard deviations (σ), which are calculated from vector means for cross-bed measurements from outcrops of these members indicate that paleocurrents flow from NB to SW. Difference of standard deviations between the two members (σW > σL) shows that the braided nature of the L-paleostream is stronger than that of the W-paleostream.From the L and W members, the writer has determined and described the characteristics of the following fluvial environments: channel-lag, point-bar, bar, natural levee, chute-fill and floodplain.Geometry of sandbody, type of accretion, succession of beddings characteristics of the cross-beddings, cyclothems, standard deviations of paleocurrents, etc. lead to the conclusion that the W-paleostream is a low-sinuosity stream and L-paleostream, a braided stream.Finally, depth and width of the paleochannel and velocities of paleostream are also discussed.
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