Natural compositional variation of the river Meuse (Maas) suspended load: a 13 ka bulk geochemical record from the upper Kreftenheye and Betuwe Formations in northern Limburg

Unambiguously pristine and largely unpolluted sediments from the Late Weich selian and Holocene infillings of the Meuse residual channels in northern L imburg (the Netherlands) have been sampled to determine the natural composi tional variation of the river's suspended load. Bulk geochemical and granulometric analyses demonstrate that about 70% of t he variation can be ascribed to hydrodynamic mineral sorting. Clay- and fin e silt-sized phyllosilicates are the most important: deterministic features , hosting the bulk of Al2O3, TiO2, K2O, MgO and trace element variability ( notably Ba, Cr, Ga, Rb and V). Quartz is abundant in the fine and coarse sa nd fractions. Na2O and the Zr-Nb-Nd-Y quartet relate to albitic feldspars a nd heavy minerals, respectively, in the coarse silt fraction. The granulome try should therefore be quantified if geochemical baseline data for a parti cular geological unit or region are drawn up and for the evaluation of pote ntially polluted sediments. Although provenance has not changed, the composition of Meuse sediments can not be considered constant over a time frame of 1000-10,000 years, due to c limatic change. Weathering of phyllosilicates in both interstadial and inte rglacial soil environments and changing relative source-area contributions alter the detrital clay-mineral supply to raise the Al2O3 and lower the K2O and MgO contents in Holocene Meuse sediments. Early diagenetic siderite an d vivianite formation in gyttjas causes relative accumulations of Fe2O3, Mn O, P2O5, Co, Ni and notably Zn above the phyllosilicate background values. These accumulations are natural and show that sediments with elevated trace metal contents are not necessarily polluted. Very early atmospheric pollut ion in relation to ore mining and smelting activities in the Roman era, how ever, probably caused elevated Pb contents in Subatlantic humic clays and p eat samples, long before the historic pollution of the Industrial Revolutio n started. The Al2O3, Fe2O3 and CaO contents are used to predict the trace-element val ues as a function of sample granulometry, siderite/vivianite and lime conte nt, respectively. As such, they can provide a sound basis for environmental researchers to determine baseline values of heavy metals in bulk samples o f fine-grained fluvial sediments.