Grain-size distribution and grain-size dependent magnetic susceptibility of sediment core GeoB18530-1

Since the weight percentages of (classifiable) IRD particles > 1 mm and (unclassifiable, but separable) IRD particles > 125 µm both largely underestimate the total content and magnetic impact of IRD, it is important to quantify also the finer IRD fractions and their magnetic susceptibilities. From each of the IRD-rich sediment units H1, I1 and H2, six magnetic cube samples of 6.2 cm³ each were combined, dried, weighed and ultrasonically suspended in water. These three slurries were successively washed through 16 stacked sieves with mesh sizes in approximately 0.5 phi steps from 4000 µm to 5 µm using a Fritsch wet sieve shaker. The sieve fractions were carefully collected, dried, weighed and measured in a Kappabridge KLY2 susceptometer. The data and therefrom-derived partial susceptibilities and cumulative distributions clearly demonstrate that the magnetically most dominant and "volatile" sediment particles fall into the 40-125 µm range. Detrital particles of such sizes are too coarse to have been current-transported over long distances and were therefore probably at least partially ice-rafted.