松江市に分布する"川津赤色粘土"について(予察)

Red clay distributed in the northern Matsue City is a peculiar red（9 R 5/3-1 YR 4/3），and is characterized by higher Al_2O_3 contents（over 30 wt％）compared with normal soils．CIA（chemical index of alteration）values given by molar portions of Al/（Al＋Na＋Ca＋K）x 100 are over 90，suggestive of significant weathering for the parent material．Although the color of this clay and CIA values are suggestive of dominant iron oxides or hydro-oxides．A possible parent material is alkaline basalt of the Matsue Formation，but chondrite-normalized REE patterns of the Kawastu red clay are characterized by relatively gentle inclination with negative Ce/Ce* and Eu/Eu* anomalies．The negative Ce* anomalie can result from explained REE alteration under reducing conditions．The Eu/Eu* negative anomalie can be explained by mixing of alkaline basalt and evolved material such as the Tertiary sediments which also occur in this district．