摘要:
黄河中游新近系红粘土粒度分布表现出明显的三峰分布,说明它是由多种成因组份构成,而且每种成因组份对整体的贡献率也不同。其粒度组成主要是以粉土粒级(5~50 μm)为主,而250 μm以上的颗粒少见。除小于1 μm和小于2 μm粒级含量变化相对稳定外,其余粒级均表现出旋回起伏的特征。大于63 μm和大于30 μm及中值曲线变幅较大,说明当时冬季风比较盛行,而且变化强度比较大;而小于2 μm粒级曲线变化相对稳定,说明当时夏季风很弱,而且没有太大变化。粒度曲线与野外岩性所得结论相一致,说明当时气候总体上是以干冷为背景,但也有干冷与暖湿的交替。野外岩性上表现为粘土层与钙结核层相互交替,粒度曲线上表现为峰谷旋回起伏的变化,同时也有古生物证据与岩石学证据相佐证。
关键词:
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黄河中游
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府谷
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新近系
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红粘土
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粒度特征
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古环境
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陕西
Abstract:
The Neogene red clay represented by the Laogaochuan section in the middle reaches of the Huanghe River exhibits a trimodal grain-size distribution, with dominant silt-sized particles (5 to 50 μm) and rare (particles) greater than 250 μm. The contents of particles less than 1 μm and 2 μm are relatively stable. The other grain sizes display a pattern of cyclic relief. The curves for the particles greater than 63 μm, 30 μm and median sizes are highly variable, implying that the Neogene climates were once cold and dry, and the winter monsoons were once highly variable in strength and prevailed over the study area. The stable variations in the curves for the particles less than 2 μm suggest that the summer monsoons were then very weak and less variable in strength. The observations of the grain-size curves for the Neogene red clay from the study area are generally supported by the litholigic and palaeontologic evidences.
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