宜昌砾石层的沉积环境及地貌意义  

Sedimentary environment and geomorphological significance of the gravel bed in Yichang

作　　者：李庭[1] 李长安[1,2] 康春国[1,3] 雷文大[1] 杨建[1] 王节涛[1] 

机构地区：[1]中国地质大学地球科学学院,湖北武汉430074 [2]生物地质与环境地质教育部重点实验室,湖北武汉430074 [3]哈尔滨学院,黑龙江哈尔滨150086

出　　处：《中国地质》2010年第2期438-445,共8页Geology in China

基　　金：国家自然科学基金项目(40771213;40672206);中国科学院地球环境研究所黄土与第四纪地质国家重点实验室开放基金项目(SKLLQG09)资助

摘　　要：宜昌砾石层上覆中更新世网纹红土,下伏白垩纪红层,共有22个岩性层组成,总厚超过100m。通过对宜昌地区剖面出露砾石层的沉积相分析表明,善溪窑和云池剖面由下至上出现冲积扇扇中-扇根亚相;李家院剖面与上述两剖面间有沉积间断,由下至上出现冲积扇扇端-扇中亚相。粒度分析也证明了该砾石层中的砂体属冲积扇中的辫状水道沉积,与沉积相分析所得结论一致。研究认为,宜昌砾石层具有典型的冲积扇沉积环境特征,主要为冲积扇扇顶部分。该冲积扇在宜昌东南地区如此大规模的发育,显示其形成时具有强大的水动力条件,通过对其形成的地貌环境意义进行探讨,初步认为,该冲积扇为长江三峡贯通的产物。据前人研究推断,宜昌砾石层的形成时代应该在1.08～0.73MaB.P.,三峡贯通应在1.0MaB.P.之前。The gravel bed in Yichang is more than 100m thick and composed of 22 layers. It lies over Cretaceous red bed and covered wjth Middle Pleistocene plinthitic red earth. The authors analyzed the sedimentary fades of the gravel bed. The upper and middle fan subfacies of alluvial fan exist in Shanxiyao and Yunchi profiles from the bottom upward. There is a hiatus between Lijiayuan profile and the above two profiles. The middle and lower fan subfacies exist in Lijiayuan profile from the bottom upward. Grain size analysis also shows that the outcropped sand body has the characteristics of braided river and alluvial fan, which is consistent with the result of sedimentary fades analysis. It is thus concluded that the very thick gravel bed in Yichang is a typical alluvial fan and seems to be mainly the upper part of the fan. Such wide development of the alluvial fan can only occur under the condition of strong hydrodynamic action. Through a study of the geomorphology and environmental significance of the formation of the fan, the authors preliminarily consider that the outcropped gravel bed in Yichang was produced by the formation of the Three Gorges. Data available also show that the gravel bed was formed in 1.08-0.73 Ma B.P., whereas the Three Gorges were formed before 1.0Ma B.P.

关 键 词：砾石层 沉积环境 沉积相 粒度 冲积扇 形成时代 

分 类 号：P512.2[天文地球—地质学]