[H-CG25] Earth surface processes related to deposition, erosion and sediment transport

[HCG25-P03] Characteristics of components decomposed from polymodal grain-size distributions and their implication for sedimentary processes: an example of lacustrine sediments in Lake Kitaura, Japan

*Naofumi Yamaguchi¹, Tsuyoshi Andou², Hirotaka Enokida³, Natsumi Nakada², Syota Yamaki^2,4 (1.Global and local environment co-creation institute, Ibaraki University, 2.Department of science, Ibaraki University, 3.Graduate school of science and engineering, Ibaraki University, 4.Asano Taiseikiso Engineering Co., Ltd. )

Keywords:Grain-size distribution, Lacustrine sediment, Sedimentary process

Grain-size parameters of sediments have been commonly used as a possible clue to reconstruct their sources and sedimentary processes. However, sediment in natural environments including lakes has frequently polymodal grain-size distribution, which makes it difficult to interpret its representative parameters. The present study attempted to decompose polymodal grain-size distributions of bottom surface sediments collected at 27 sites in Lake Kitaura and to examine the relationship between the logratio of the components and sedimentary processes. For decomposition of the grain-size distribution of each sample, we determined the number of components based on the value of Bayesian information criterion and separated it into lognormal distributions by using expectation–maximization algorithm. As a result of decomposition, the grain-size distributions of most of the present samples were separated into four common components. The finer three of the four common components had similar proportions, which suggested that the sediments originated in the lake. By contrast, the proportion of the coarsest component varied among the present samples. The results of logratio analysis indicated that the logratio of the coarsest component reflected the sedimentary processes associated with water depth, distance from the nearest lakeshore, and local bottom topography.