Desert-steppe migration on the Loess Plateau at about 450 kaBP
关中平原420-350 ka BP的古土壤与环境

The fourth paleosol (S4) which had changed into a residuum of the Brunhes Epoch (780,000 yr BP) at Shuangzhu in Chang'an, Koujiapo in Xi'an, Tianjiapo in Lantian and Hejiacun in Baoji developed over about 40 ka years. It consists of 4 horizons, the 1st one (uppermost) is a well developed reddish brown clay horizon (Bts), the 2nd is a dark yellowish brown weathering-cracked loess horizon (Cs) with red ferruginous clay films, the 3rd is yellowish brown weathering-cracked loess horizon (Cl) without the red ferruginous clay films, and the 4th is CaCO3 nodules horizon (Ck). In the Bts horizon, CaCO3 was leached away, Sr being trace element moved obviously and reached Ck horizon located at the bottom of the weathered profile, which indicates depth affected by weathering-leaching surpassed that of the Bts horizon and reached the lower boundary of the Cl horizon. In the Bts horizon, Fe2O3 and Al2O3 removed intensely also and into Cs horizon. In the weathered profile consisting of Bts, Cs and Cl, pH values are low, clay content is high, and Fe2O3 and Al2O3 were formed, which shows intense chemical weathering took place. The development of the fourth paleosol as a residuum suggests that a moist subtropical climate prevailed 420,000-350,000 yr BP in the southern part of the Loess Plateau in China. Its profile is Bts-Cs-Cl-Ck-C. When the paleosol developed, mean annual temperature and rainfall were about 16oC and 1000 mm respectively, about 3oC higher and 400 mm more than those at present in the Guanzhong Plain.