Sedimentary features of the seismo-turbidites, Lake Biwa, Japan

Seismo-turbidite layers are deposited at the foot of the steep slope of the half graben in which Lake Biwa has accumulated. Sedimentary studies, espec ially of grain-size distribution of selected turbidites provide excellent i nformation for clarifying the distinctive features of general seismo-turbid ites. Development of the two constituent sublayers (lower sandy sublayer an d upper silt sublayer), lack or limited appearances of traction-indicating structures and characteristic grain-size distribution in the two constituen t sublayers are most remarkable and significant. The characteristic grain-s ize distribution features are coarse tail grading in a relatively thick san dy sublayer, exceptionally rapid distribution grading through the thin boun dary interval between the two sublayers, height increase and fluctuation of the silt mode, and high clay content. Brief discussion was made on the cau ses of these sedimentary features. The need and importance of further compa rative studies of various turbidites known triggering forces are emphasized . (C) 2000 Elsevier Science B.V. All rights reserved.