Stratigraphy of multiple piston-core sediments for the last 30,000 years from Lake Biwa, Japan

Analysis of seven piston cores obtained from three sites in Lake Biwa provide a detailed stratigraphy of the lake sediments for the last 30 kyrs. Description of lithology and measurement of magnetic susceptibility reveal occurrence of volcanic ashes at ten horizons, that were visually observed or microscopically found from clayey sediments. Most ash layers are observed in multiple cores from the three sites and also in earlier cores, establishing correlation and age assignment of the core sediments. This result demonstrates usefulness of magnetic susceptibility data in finding dispersed volcanic ashes. The age-depth curves deduced from published tephra ages show that significant difference in sedimentation rates occurs in Lake Biwa. The central part of the depression is characterized by homogeneous sediments deposited with a high sedimentation rate. The 250-m-thick lacustrine clay in this sub-basin has great potential for high-resolution study of the past environment and paleomagnetism for the last 0.5 Myr.