5.1 Grain-size of sediments
The sediments were assessed using the classification scheme of Folk
[1974](Fig. 3). Sediments range from silty sand to silt and mud,
both the new samples processed here and those from the earlier study we
integrate with here {Clift, 2019 #152}. The grain size variation in
single samples can be better assessed by plotting the proportion of each
grain size fraction as a spectrum (Fig. 4). We see generally good
sorting (positive kurtosis) and a negative skew, meaning a dominance of
the finer grain sizes and a tail of coarser grains comprising a
diminishing proportion of the sediment. This is especially true for the
coarsest grained sediments. The vast majority of the sediment considered
here is classified as fine sand to silt, with only small amounts of
medium and coarse sand in a minority of samples, three from Site U1456
dated at 1.92–1.32 Ma and one from Site U1457 at 3.02 Ma. Three of the
new samples do contain significant volumes of medium and even coarse
sand (3.39, 7.00 and 7.27 Ma). The spot size of the laser used for the
U-Pb dating means that grains smaller than ~30 µm were
not considered in this study. Depending on the sample this represents a
wide range of the total sediment load. Only 9% of Sample U1456A-51F-3,
100-110 cm was less than 30 µm, while 89% of Sample U1456A-70F-2, 10-16
cm is smaller than that threshold. See Table 2 for full results.