THE IMPACT OF CLIMATE-CHANGE ON THE BULK AND CLAY GEOCHEMISTRY OF FLUVIAL RESIDUAL CHANNEL INFILLINGS - THE LATE WEICHSELIAN AND EARLY HOLOCENE RIVER MEUSE SEDIMENTS (THE NETHERLANDS)

Fine-grained fluvial residual channel infillings are likely to reflect systematic compositional changes in response to climate change, owing to changing weathering and geomorphological conditions in the upstrea m drainage basin. Our research focuses on the bulk sediment and clay g eochemistry, laser granulometry and clay mineralogy of Late-glacial an d Early Holocene River Meuse (Maas) unexposed residual channel infilli ngs in northern Limburg (The Netherlands). We demonstrate that residua l channel infillings register a systematic bulk and clay compositional change related to climate change on a 1-10 k-yr lime-scale. Late-glac ial and Holocene climatic amelioration stabilised the landscape and fa cilitated prolonged and intense chemical weathering of phyllosilicates and clay minerals due to soil formation. Clay translocation and subse quent erosion of topsoils on Palaeozoic bedrock and loess deposits inc reased the supply of smectite and vermiculite within River Meuse sedim ents. Smectite plus vermiculite contents rose from 30-40% in the Pleni glacial to 60% in the Late Allerod and to 70-80% in the Holocene. Youn ger Dryas cooling and landscape instability caused almost immediate re turn to low smectite and vermiculite contents. Following an Early Holo cene rise, within about 5000 yr, a steady state supply is reached befo re 5 ka (Mid-Holocene). Holocene sediments therefore contain higher am ounts of clay that are richer in high-Al, low-K and low-Mg vermiculite s and smectites compared with Late (Pleni-)glacial sediments. The impo rtance of clay mineral provenance and loess admixture in the River Meu se fluvial sediments is discussed. (C) 1998 John Wiley & Sons, Ltd.