粒度分析から推定される余呉湖の発達史

Abstract

In order to investigate the developmental history from the viewpoint of paleohydrological en-vironment, the writers have examined the granulometric analyses on the core sample obtained inLake Yogo-ko.Although the sediment is thoroughly Gyttja, granulometric analyses show the existence of thealternation of two kinds of strata with 1～1.5 m interval.One is coarser stratum composed by fine sand and silt, and the other is clay dominant stratum.In that alternation, the content of the former seems to be about 50% in amount and of the latterseems to be approximately 70-80% in amount.The coarser stratum contains much organic carbon and therefore more humic material. Ac-cordingly, the specific weight of that stratum is relatively light. The writers have discussed aboutthe past limnetic environment under which the coarser, blackish and high organic material was de-posited.