岩溶洞穴古河漫滩沉积物特征及其沉积环境演变——以山王洞中段为例

The characteristics of karst cave ancient floodplain sediment and environment evolution:A case study in Shanwang cave

为揭示岩溶洞穴沉积物对沉积环境与沉积过程的指示作用，文章在分析双河洞洞系形成过程及山王洞区域地质调查资料的基础上，选取贵州山王洞中段古河漫滩沉积物为研究对象，采用粒度分析法与萨胡公式对洞穴沉积物粒度特征与沉积环境的相关性进行分析，推断不同沉积韵律期的沉积环境演变过程，研究结果表明：（1）古河漫滩表层沉积物以极细砂、粉砂和黏土为主，平均含量达94．42％，且中上部含有一层粗砂砾夹层；（2）沉积模式主要为跳跃和悬浮沉积，水动力条件整体稳定，搬运颗粒粒径平均值为637μm，其最大沉积物颗粒粒径为864．2μm；（3）以沉积物粒度特征为依据，将古河漫滩沉积过程划分为三级沉积韵律，一级沉积韵律厚度为404～275cm，二级沉积韵律厚度为285～165cm，三级沉积韵律厚度为165～0cm。上述研究为确定区域侵蚀基准面和地层升降运动过程提供有力证明，也为山王洞古气候环境研究提供了重要依据。

To reveal the influence of karst cave sediments on the sedimentary environment and the sedimenta- ry process, this study was conducted in the middle range of Shanwang cave, Guizhou, in conjuction with pre- vious studies of the cave development and associated geological information of the area. The sediment grain size analysis was done and on this basis Sahu＇s formula was employed to analyze the correlation of sedimenta- ry environment and the sediment particle gradation, from which the evolution of sedimentary environment in different cave sedimentary cycles was assessed. The results show that, （1） in the surface of ancient flood- plain, the sediments comprise very fine sand, silt and clay, with an average content of 94.42%, where there is an intercalated coarse gravel layer; （2） the sedimentary pattern was represented by the uniform deposition process which was dominated by steady flow over the cave floodplainl as a result the average sediment parti- cle size was 637μm, with a maximum size of 864.2 μm; （3） According to the characteristics of granularity, the ancient floodplain deposition can be divided into three layers deposited in different sedimentary environ- ments~ the first layer is 404-275 cm in thickness, the second one is 285-165 cm thick and the third 165- 0 cm in thickness. The results provide important information for the determination of regional erosion datum and the study of crustal movement of the area. In the search of paleoclimate of the Shanwang cave area. meantime, it provides an strong evidence for the research of paleoclimate of the Shanwang cave area.