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

To reveal the influence of karst cave sediments on the sedimentary environment and the sedimentary process, this study was conducted in the middle range of Shanwang cave, Guizhou, in conjuction with previous 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 sedimentary 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 floodplain, 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 floodplain; as a result the average sediment particle size was 637 μm, 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 environments; 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 meantime, it provides an strong evidence for the research of paleoclimate of the Shanwang cave area.