Logratio analysis of components separated from grain-size distributions and implications for sedimentary processes: An example of bottom surface sediments in a shallow lake

The grain-size distributions of sediments can yield important information about sediment provenance and sedimentary processes; however, grain-size distributions are frequently polymodal, rendering analyses difficult. To improve analyses of polymodal grain-size data, the present study decomposed the grain-size distributions of bottom surface sediments from Lake Kitaura, a shallow lake in Japan, into lognormal distributions and performed logratio analysis of their mixing proportions. The polymodal grain-size distributions of the studied samples were separated into four common components at most sites. This logratio analysis revealed clear differences in the characteristics of the spatial distributions of the separated grain-size components. The logratio values indicated that the three finer components were uniformly deposited within the lake, whereas the coarsest component was spatially diverse, reflecting differences in their sources and sedimentary processes. These results demonstrate the effectiveness of decomposition and logratio analysis of polymodal grain-size distributions for estimating sedimentary processes. This method can be applied to modern sediments and for palaeoenvironmental reconstructions using sediment cores.