Laser-diffraction and pipette-method grain sizing of Dutch sediments: correlations for fine fractions of marine, fluvial, and loess samples

To evaluate correlations between silt and clay fractions determined by pipette method and laser diffraction, samples from Dutch fine marine, fluvial, and loess deposits were analysed by both methods. For fluvial deposits, correlations for fractions <2 and >50 mum were excellent (R-2 > 0.95), those for 2-4, 4-8, 16-32 and 32-50 mum were satisfactory (R-2 = 0.80 - 0.95), while that for the fraction 8-16 mum had an R-2 of only 0.68. For marine deposits, correlations for <2 and >50 mum were in the same range, but those of all other fractions except 8-16 mum were lower. In the loess samples, correlations for all but the 8-16 mum fraction were unsatisfactory. Laser diffraction gave 42% of pipette clay in marine samples, and 62% in fluvial and loess samples if regressions are forced through 0. Sand fractions detected by laser diffraction were 107% of the sieve fraction in marine samples, and 99% in the fluvial samples. Correlations for fractions smaller than reference size are generally better than those for individual size fractions. Both the 2 mum and the 50 mum boundary cause problems in the comparison. The first because of platy shape of clay minerals, and the second due to both a change in method in the pipette/sieving procedure, and to non-sphericity of particles. Apparently, correlations for clay- and silt-size fractions obtained by pipette method and laser diffraction will be different for each type of sediment.