IODP Proceedings    Volume contents     Search



Results are shown in Figures F1 and F2 and in Table T1. Raw data of frequency distribution is provided in GRAINSIZ in “Supplementary material.”

Errors derived from nonhomogeneity of samples were mostly <0.2 ϕ, except for mode diameter, in terms of standard deviation of each representative value derived from measurements of three different aliquots from each of 27 selected samples (Fig. F3). Correlation of standard deviation to 10-percentile and median diameter is a nonzero value by >0.99 probability, and that to mean diameter is >0.98 probability (Fig. F4). Smaller diameters tend to show smaller standard deviation values. Thus, a difference of ~0.2 ϕ in median diameter between different samples can be regarded significant if the median diameter is <7 ϕ.

Hemipelagic mud grains are coarsest in the uppermost 94 m interval, with median diameters of ~7.2 ϕ. However, the 42–94 mbsf interval is characterized by a broadened grain size frequency distribution. In contrast, median and 10-percentile diameters differ little from the uppermost 42 m interval; 90-percentile diameter is obviously coarser between 42 and 94 mbsf than in the uppermost interval. Frequency distributions are also flattened because of the low frequency of modal grain size (Fig. F1).

Grain size generally fines downcore with fluctuations in the 94 to 165 mbsf interval. Median and 90-percentile diameters fine from 7 to 8 ϕ and from 5 to 6 ϕ, respectively, whereas 10-percentile diameter fines slightly from 9.6 to 10 ϕ (Fig. F2A).

Hemipelagic mud grains are finest from 165 to 380 mbsf (Figs. F1, F2). In this interval, grain size shows narrow, sharp frequency distribution, and median diameter is almost steady at ~8 ϕ. A few excursions were observed between 254 and 214 mbsf, where median diameter coarsens to 6.5 ϕ, and between 351 and 363 mbsf, where median diameter coarsens to 5.3 ϕ.