Environmental magnetism of brackish-water sediments from Lake Tougou-ike on the Japan Sea coast

Abstract

We made rock magnetic measurements of core sediments from a brackish-water lake on the Japan Sea coast, Lake Tougou-ike in Tottori Prefecture. The core samples mostly consist of non-glacial varved sediments and massive clay and silt, including volcanic ash layers. We measured low-field magnetic susceptibility, anhysteretic remanent magnetization (ARM) and isothermal remanent magnetization (IRM) of discrete samples at about 10 cm interval. These magnetic-concentration parameters show clear correlation with lithology of the sediments. In particular, sandy parts of the non-glacial varves are suggested to contain greater amounts of coarse-grained magnetite. Several horizons within the non-glacial varves are characterized with significantly high values of coercivity parameters, corresponding with intercalations of thin mud layers. Thermal demagnetization experiments of three component IRMs and measurements of hysteresis parameters indicate presence of hematite at these horizons. Factor analysis of the magnetic parameters combined with mineral magnetic data revealed a characteristic component contributed by the magnetic-concentration parameters and the feldspar content, which is interpreted as representing detrital input of volcaniclastic materials. It is suggested that coercivity parameters would be particularly useful for detecting detrital inputs and estimation of their origin.