Geochemical history of ancient Lake Biwa in Japan—chemical indicators of sedimentary paleo-environments in a drilled core
Abstract A comparison is made between the geochemical compositions of drilled sediment core samples from Lake Biwa and samples of surface sediments and from land around Lake Biwa to estimate paleo-water depth, spatial variability and past changes in sediment sources. The AlFeMn × 10 diagram indicates that Lake Biwa has been an oligotrophic lake since its formation. An investigation of the origin of a positive correlation between water-depth and the Mn/Al ratio in surface sediments is made and the historical change of paleo-water depth in Lake Biwa proposed by Koyama et al. (1985) verfied. Demonstrated are the usefulness of both Ti/Al ratio and REE pattern to detect changes in sediment sources and geochemical discontinuities in four layers which should indicate unconformities are found. My data could be supporting evidence for the chronological assignment of Takemura (1990). An explanation is given for the historical changes of source materials in drilled core samples associated with tectonic changes on the basis of the historical basin development postulated by Yokoyama (1984).