Theoretical investigations on models of the developmental processes of erosional features show that the time variations in erosional force have more sensitive influence on the time fluctuation of eroded material, such as sediments in lakes, than that of the quantity representing erosional features, such as volume of mountains. Time sequences of grain-size distributions from the Pleistocene sediments in Lake Biwa, central Japan indicate dominant periodicities of about 40,000 and 20,000 yr, very close to those predicted from the Milankovitch theory. The time variations of the grain-size parameters which may be indicators of erosional forces are very similar to that of the caloric summer insolation in the Northern Hemisphere.

A time sequence of grain size distributions from the Pleistocene sediments in Lake Biwa, located in the central part of Japan (35° N, 136° E), has dominant periodicities of 41,000, 23,000, and 19,000 years which are very close to those predicted from the astronomical theory of paleoclimate introduced by Milankovitch. The time variation of the grain size is very similar to that of insolation of caloric summer in the Northern Hemisphere.

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Time series of grain-size distributions from Pleistocene sediments deposited in Lake Biwa during the past 550 millennia show dominant periods of 40,000 and 20,000 yr that are very close to those predicted by the Milankovitch theory, as well as a period of about 70,000 yr not directly predicted by this theory. The 70,000-yr period is strongest, followed by the 20,000-yr period. The sequences also show that coarser particles were deposited, in general, during strong solar insolation, whereas finer particles were deposited during weak insolation.

Age-scaling is attempted using the vertical profile of bulk density of the uppermost clayey layer (240-250 m in thickness) in a new deep core sample from Lake Biwa. At first, the empirical porosity-depth relation is physically examined on the basis of a consolidation theory. The vertical profile of bulk density in the upper 180 m of the clayey layer is approximately described by the empirical bulk density-depth relation, which is derived from the porosity-depth relation. By applying the age by fission-track dating to the age-depth relation analytically derived from the bulk density-depth relation, an average sedimentation rate in the upper clayey layer is estimated to be 0.033 g•cm-2•yr-i and then the age-depth curve is obtained for the upper clayey layer. The age-depth curve in the lower clayey layer from 180 to 240 m in depth is obtained under the assumption that the sedimentation rate is constant through the whole clayey layer. The result shows that the age of the base of the clayey layer at about 240 m in depth is estimated to be 0.63 Ma.