摘要
陕西老高川红粘土剖面粒度表现出明显的三峰分布特征,说明它是由多种成因组分所构成,而且每种成因组分对整体的贡献率也不同。其粒度组成主要是以粉土粒级(5～50μm)为主,且10～50μm粒级含量高于5～10μm,>250μm颗粒少见。除<2μm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。>63μm、>30μm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<2μm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,同时也有古生物与岩石学证据相佐证。磁化率曲线变化说明榆社期较保德期气候暖湿。
Sample analyses show that the Neogene red clay at the Laogaochuan section exhibits a trimodal grain-size distribution,suggesting that the red clay is composed of components of multiple origins and that components of different origins make different contributions to the total. The silt-sized grains （5-50μm） are predominant, of which the content of grains of 10-50μm in size is higher than that of grains of 5-10μm and grains 〉250μm in size are rare. The mean, 〉63μm and 〉30μm grain-size curves are highly variable, while the 〈2μm grain-size curve is relatively stable. The features indicate that the Neogene climate was mainly dry and cold and the winter monsoons had once changed greatly in strength and prevailed over the study area and that the summer monsoons were relatively weaker with little change. The changes of the grain-size curves are supported by the lithologic and biologic evidence, suggesting that the climate then was mainly dry-cold and sometimes alternately warm-wet and cool-dry. The lithology in the field is manifested by alternation of clay beds with calcic concretionary beds and the grain-size curves are manifested by fluctuations of peaks and valleys. The susceptibility curve shows that the climate of the Yushean Stage was warmer and wetter than that of the Baodean Stage.
出处
《中国地质》
CAS
CSCD
2005年第3期496-501,共6页
Geology in China
基金
国家自然科学基金项目(49972004
40372202)资助。
关键词
陕西老高川
红粘土
粒度
磁化率
古环境
Laogaochuan
red clay
grain-size
susceptibility
paleoenvironment
