EROSIONAL ENVIRONMENT AND GRAIN-SIZE VARI ATION IN PLEISTOCENE LAKE-SEDIMENTS

Grain size variation in sediments that have had relatively high sedime ntation rates may provide information on the paleoerosional environmen t that has developed erosional features around a lake. Statistical ana lysis shows that grain size variations in semi-closed Lake Biwa sedime nts during the past 235,000 years have periods of about 20,000. 40,000 . 60,000 and 130,000 years. Of these, the 20,000- and 40,000-yr period s respectively are directly related to the precessional and obliquitic al parameters of the Milankovitch theory, but 60,000- and 130,000-yr p eriods are not. The 130,000-yr period may refer to a 120,000-yr period of eccentricity. The same statistical analysis indicates that there a re 20,000-, 40,000-, 70,000- and 110,000-yr periods in the deltaO-18 d ataset of RC11-200, and 20,000-, 40,000-, 60,000- and 130,000-yr perio ds in the atmospheric CO2 dataset of the Vostok ice core. The 110,000- and 130,000-yr period may correspond to 100,000- and 120,000-yr perio ds of eccentricity. Most periods found for the grain size variations i n Lake Biwa sediment also have been found in datasets obtained from fa r-off locations, evidence that the changes in the paleoerosionai envir onment of lacustrine sediments in East Asia are closely connected to g lobal climatic changes.