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-paleosol sequence spanning the last 130,000 yr. Depth functions of micromorphological features, magnetic susceptibility, calcium carbonate, organic carbon, and median grain size provide the basis for pedosedimentary and associated paleoenvironmental reconstructions of three paleosol 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 crust formation, or even freeze-thaw modification. The Sm pedocomplex represents 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 pedogenically developed, although erosion, reworking, and mixing by water have partly homogenized the property depth functions. (C) 1995 University of Washington.