Variations in chemical composition and particle size of dune sediments along the west coast of Jutland, Denmark

摘要

Geochemical and textural variations in frontal dune sediments along the western coast of Jutland, Denmark, have been investigated in order to identify possible sediment 'provinces' and transport pathways. An understanding of sediment sources and sinks is important for both for an understanding of the nature of sedimentary environments and for applied coastal engineering and management purposes. Four coastal sectors were identified on the basis of geochemical composition. One sector is compositionally different from the other three units, having higher concentrations of the trace elements Ni, Cr, V, Sc, Zn, Pb, Ba, Zr and many rare earth elements. Dune sediments on this section of coast also have higher Al_2O_3 to K_2O ratios and lower Al_2O_3 to Fe_2O_3 ratios, reflecting a lower content of feldspar and higher content of heavy minerals. It is inferred that different, or additional, sediment source(s) have supplied sediment to this section of coast. Beach nourishment has contributed to the observed compositional differences, but previous data obtained from the Lodbjerg area indicate that aeolian sands on this section of coast naturally have a relatively high Si, Fe and Ti content, reflecting high quartz/feldspar ratio and relatively high content of heavy minerals, compared with those on other sections of the coast. Frontal dunes along the most northern section show high abundances of K_2O, Rb and Ba, reflecting a relatively high K-feldspar content derived from local sources. Alongshore trends were also identified in the mean particle size and sorting of the frontal dunes, although there is no direct correspondence with the observed geochemical differences. Three coastal units can be identified on the basis of particle size. Frontal dune sediments in the middle section are relatively coarser and less well-sorted than those to the north and south, probably reflecting both the addition of beach nourishment material and greater exposure to strong westerly winds, which are a capable of transporting a wide range of particle sizes. The three units defined on this basis do not correlate directly with the units defined on the basis of geochemical composition.