水月湖細粒堆積物に認められる過去2, 000年間の風成塵・海水準・降水変動の記録
1995 年 104 巻 1 号 p. 69-81
詳細
1995 年 104 巻 1 号 p. 69-81
Mineralogical characteristics of last 2, 000 year records in a meromictic lake, Lake Suigetsu, are the indicators of eolian dust concentrations, sea-level and rainfall changes in central Japan.Lake Suigetsu sediment records shows that there was no large influx of terrestrial materials intolake basin. Sequential changes of illite crystallinity and quartz/illite ratio in Late Quaternaryfine-grained sediments at Site 794 and Site 795 of ODP Leg 127 of were well correlated tostandard recocds of oxygen isotope change by Prell et al.(1986). This suggests that theseparameters are useful to detect eolian dust concentration within sediments. In other words, occurrence of hydrated illite and small concentration of illite suggest that paleosols were greatlyformed under wet climate in northern China. Sea-level and rainfall changes were detected byiron mineral compositon and chlorite/illite ratio.Investigations show that climatic changes in northern China were parallel to sea-levelchanges of the Wakasa Bay in southern part of the Japan Sea. In 250, 820, 1170, 1320, 1500and 1889 A.D., sea-level was risen in the Wakasa Bay when northern China was in wetclimate. It is because that Asian monsoon was active in globally warm cliate at these times, andthat active monsoon took humid atmosphere into northern China. In 250, 820, 1050-1200, 1320, 1500 and 1880 A.D., there seems to have been heavy rainfall around Lake Suigetsu with sea-levelrising in the Wakasa Bay. This suggests of influxing of Tsushima Current, supplying humidatmosphere and rising of sea-level. In 350-550 and 1350-1400 A.D., precipitations were heavyin the Wakasa region, though there are no rising of sea-level, and dry and cool climate in China.
