Geochemical evidence for weathering in northwestern European loess on a sub-millenial scale during the last Ice Age
This study seeks to determine the extent to which chemostratigraphy can supplement other stratigraphic tools in determining the effects of climate change in loess-palaeosol sequences. Geochemical change has been used to illuminate the effects of glacial/interglacial climate change in Chinese loess-palaeosol sequences; less work has been done to examine the effects of stadial/interstadial climate change and little work has been carried out in Europe on either aspect. Two loess-palaeosol sites were selected in northwestern Europe that were known to provide good records of the last ice age. This study has produced detailed descriptions of variation in concentrations of the major, minor and rare-earth elements. These are compared with variation in the standard sedimentological parameters (grain size, organic carbon content and carbonate content) and in enviromagnetic characteristics, which are accepted as palaeoclimate proxies. The existing polymineral-based luminescence chronology at each site has been enhanced using a quartz-based approach,which broadly confirms the accuracy of previous ages and generates estimates of increased precision. That chronology facilitates comparison of these analyses with evidence for palaeoclimatic: change in the wider record, including GRIP ice-core data. Grain size is shown to be a strong proxy for variation in mean wind strength and in accumulation rates which can be correlated in detail with GRIP. The study has established that geochemical heterogeneity now apparent at the sites has been imposed by weathering. Carbonate weathering is a reliable indication of major pedogenic episodes but its detailed interpretation is tempered by carbonate mobility. Silicate weathering occurs at lower intensity than carbonate weathering but is a permanent record since silicates are not subject to reprecipitation under these conditions. The study concludes that chemostratigraphy is a climatological proxy, detecting periods of significant amelioration. It is not a replacement for conventional proxies, it complements them and provides additional evidence upon which climatic reconstructions can be made.