CLAY MINERALOGY AND MAJOR ELEMENT CHEMISTRY OF THE EARLY QUATERNARY AND LATE MIOCENE PALEOSOLS ON PENGHU ISLANDS (PESCADORES), TAIWAN

Abstract

Clay mineralogy and whole-soil major element chemistry of an early Quaternary red soil and two late Miocene paleosols between basalt lavas on Penghu Islands (Pescadores), Taiwan, were studied to compare properties of soils from the different periods. The early Quaternary red soil consists of a kaolinite and smectite clay assemblage. The late Miocene paleosols are rich in kaolin minerals. The amounts of Si, Fe, and Al in the three profiles are the mineralogical differences. The depth distributions for clay and free Fe oxide contents suggest that the early Quaternary red soil formed in at least two stages. The early Quaternary red soil was classified as fine, mixed, hyperthermic, Typic Rodustalf. The late Miocene paleosols were classified as fine, kaolinite, hyperthermic, Typic Rhodic Paleustalf. The late Miocene paleosols contain more clay, lower SiO2/Al2O3 and SiO2/(Al2O3 + Fe2O3) molar ratios, averages of 2.5 and 1.7, respectively, and higher chemical indexes of weathering than the early Quaternary paleosol. The SiO2/Al2O3 and SiO2/(Al2O3 + Fe2O3) molar ratios and Mn2+ and Mg2+ distributions showed zigzag patterns, suggesting that changes in sea level influenced the early Quaternary profile during the soil formation.