A high-resolution micromorphological record of changing landscapes and climates on the western Loess Plateau of China during oxygen isotope stage 5

The micromorphological characteristics of a continuous set of black samples from 24-38 m depth in a well section on Jiuzhoutai Mountain, Lanzhou, Chin a, are described. The shape of the magnetic susceptibility curve, together with previously published radiocarbon, luminescence and geomagnetic dates, indicates that this sample set encompasses the whole of the last interglaci al (S1) palaeosol complex, and extends into the overlying and underlying lo ess (L1 and L2) units. Seven pedosedimentary units are recognised on the ba sis of trends in the bulk properties and the key micromorphological indicat ors (excrements, textural concentrations, shell fragments, and calcite and gypsum features). High rates of loess deposition, with significant cryogeni c activity, gypsum precipitation and only weak bioturbation, characterised Oxygen Isotope Stage (OIS) 6 and OIS 4 at Lanzhou. Depositional rates were moderately high in OIS 5d and 5b, with slightly higher bioturbation and no significant cryogenesis or gypsum precipitation. OIS 5e, 5c and 5a were mar ked by low rates of accretion, more extensive bioturbation and limited leac hing. This reconstruction reflects the pedosedimentary responses to fluctua ting dominances of monsoonal controls during this period of global climatic change. Comparison of earlier micromorphological results from sites to wes t and east of Lanzhou along a dry to humid climatic gradient indicate a cle ar regional pattern with reduced loess accumulation rates and enhanced biot urbation and leaching in the humid east (Tianshui and Xian). Clay transloca tion occurred only in OIS 5e at Xian, the warmest and most humid site on th e transect. (C) 2001 Elsevier Science B.V. All rights reserved.