THE S1 PALEOSOL ENVIRONMENTAL RECORD INTERPRETED THROUGH SOIL DEVELOPMENT AND WEATHERING INDICES

Pedogenic and weathering processes are intricately related to paleoclimate evidence in loess. Soil processes (clay formation and translocation, carbonate concentration, and iron alteration and translocation) are all tied to weathering reactions that occur in the soil. Proxy indicators reveal environmental change, but the environment itself may alter the proxy indicators. Is the paleoclimate evidence biased by inherent complexity? One way to address this quandary is to investigate specific soil formation and weathering processes. This study applies quantified soil development indices and weathering indices and compares these against existing climate proxy indicators for the S1 Paleosol in the Chinese Loess Plateau.

Six field locations were surveyed and sampled in two northwest-to-southeast transects in the Chinese Loess Plateau. A range of field data (horizonation, color, texture, structure, carbonate morphology) was used to calculate a profile development index modified from Harden's (1982). The index was applied to the entire S1 profile at each location, and to segments within the S1 profile. Samples were taken for chemical analysis to establish leaching trends. Inductively coupled plasma optical emission spectrometry (ICP-OES) achieved composition for 10 major elements of samples taken at 10 and 20 cm intervals in the profile. Weathering and leaching indices calculated ratios of more mobile to more stable elements. These indicated degrees of chemical weathering at specific horizons, but also indicated translocation and enrichment of certain elements.

Profile development indices demonstrated a separation of paleosol units within the S1 stratum at the cool/dry (northwest) ends of the sampling transect, but verified significant soil welding toward the warm/moist ends of the transect (southeast). Soil welding has been suggested as a complicating factor in the use of key locations as primary paleoclimate records. Weathering and leaching indices indicate a higher degree of chemical activity within the paleosol layers, separated by less elemental translocation in intervening loess subunits. Chemical weathering supports the soil welding evidence. In fact, chemical alteration is evident as translocation into the lower L2 loess stratum immediately below the S1 paleosol sequence.