PALEOENVIRONMENTAL SIGNIFICANCE OF A PALEOSOL COMPLEX IN CHINESE LOESS

Several studies of loess-paleosol sequences have been conducted with the objective of reconstructing the monsoonal climate changes in East Asia, but pedocomplexes have not been identified and studied. In this study, a pedocomplex was studied with the objective of evaluating paleoenvironmental changes. The data show that the paleosol S5 of the Brunhes (780,000–0 yr B.P.), which developed over about 100 ka, is a pedocomplex and varies in thickness from 2.2 to 6.5 m. The paleosol is located at the Liujiapo near Xi’an, Renjiacun, near Baoji and Yaergou near Changwu and consists of four to five horizons. The first horizon (uppermost) is a well developed reddish brown clay horizon (Bts); the second horizon is a light reddish brown weathering-cracked loess (Ccs); the third is a dark yellowish brown weathering-cracked loess (Cs); the fourth is a light yellowish brown weathering-cracked loess (Cl); and the fifth horizon consists of CaCO3 nodules (Ck). Weathering-cracked loess horizons have not previously been found in Chinese paleosol. The clay component is montmorillonite-illite with some kaolinite minerals. The pedocomplex suggests that a moist subtropical climate prevailed from 570,000 to 470,000 years B.P. in the central and southern parts of the Chinese Loess Plateau. Its profile is Bts-Ccs-Cs-Cl-Ck-Co in the Xi’an, Baoji areas and Bts-Cs-Cl-Ck-Co in the Changwu area. When the pedocomplex developed in the Xi’an and Baoji areas (southeastern Loess Plateau), the mean annual temperature and precipitation were about 16 °C and 1100 mm, respectively, about 4 °C higher and 500 mm more than at present. In the Changwu area (central Loess Plateau), the mean annual temperature and precipitation were 15 °C and 900 mm, about 6 °C higher and 300 mm more than at present. In the typical interglacial developing the S5, the Qinling Mountains lost their function as the boundary between the subtropical and temperate zones of China.