PEDOSEDIMENTARY RECONSTRUCTION OF A THICK LOESS PALEOSOL SEQUENCE NEAR LANZHOU IN NORTH-CENTRAL CHINA

A 38-m well section near Lanzhou at the semiarid western margin of the Loess Plateau, China, contained a continuous, high-resolution loess-p aleosol sequence spanning the last 130,000 yr. Depth functions of micr omorphological features, magnetic susceptibility, calcium carbonate, o rganic carbon, and median grain size provide the basis for pedosedimen tary and associated paleoenvironmental reconstructions of three paleos ol complexes (S1, Sm, and S0). Each pedosedimentary stage reflects the interaction of changing intensities of controlling monsoonal forces. Three periods of reduced dust inputs and enhanced pedogenic activity, notably bioturbation and weak leaching, can be identified from within the S1 pedocomplex. These ''soil-forming intervals'' were separated by phases of varying land surface instability characterized by arid dust deposition, semiarid accretionary pedogenesis, water reworking, and c rust formation, or even freeze-thaw modification. The Sm pedocomplex r epresents an interval of relatively rapid dust accumulation with only minimal syndepositional modification and minor pedogenic alteration at ephemeral land surfaces. The S0 pedocomplex is clearly more pedogenic ally developed, although erosion, reworking, and mixing by water have partly homogenized the property depth functions. (C) 1995 University o f Washington.