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doi:10.2204/iodp.proc.345.115.2014

Saw cuttings samples

Fifty-five samples were collected from Holes U1415G–U1415J, U1415N, and U1415P, including three samples obtained from single, long lengths of core that were cut separately on the core-splitting “super saw.” Three different grain sizes were collected from many samples:

1. An unsorted “mud sample,”

2. A >10 µm sample from the filter, and

3. A <10 µm clay sample obtained by centrifuging the supernatant (see “Collection of core saw cuttings” in the “Methods” chapter [Gillis et al., 2014]).

However, in some samples no material remained on the 10 µm sieve, and no material of this size was collected. All but the clay-sized samples were weighed and packaged in sealed plastic bags and entered into the IODP archive. The length of cut core was measured, but the lengths were adjusted to compensate for the dimensions of samples with less than the full 5.5 cm width of the core.

From this work, 4460 g of bulk mud as well as a >10 µm sample was recovered from 4050 cm of the cut core. The weight of the <10 µm fraction was not measured on the ship. The relationship between the length of core cut (in centimeters) and grams of cuttings recovered is shown in Figure F1. The linear relationship shows a systematic recovery rate of >1 g recovered per centimeter of core cut. This apparent rate will increase when the clay-sized fraction is included in the calculation. The significance of this linearity is that all samples show a uniform yield, such that the results of X-ray diffraction (XRD) and chemical analyses of all samples may be reasonably compared.

Wash water from the cutting of each sample was milky, indicating that sawing created clay-sized (<2 µm) particles. To test whether the collection of this material was necessary, the three size fractions from Section 345-U1415J-8R-1 were each analyzed by XRD; the results are compared in Figure F2. The diagram shows that the green trace of the clay-sized suspension systematically shows taller peaks for phyllosilicates and lower peaks for plagioclase and pyroxene than either the bulk sample or the >10 µm sample. Thus, the sawing process fractionates minerals by grain size. Preliminary calculations show that this clay fraction may contribute more than one-third of the total mass of the sample. The clay-sized (<2 µm) fraction is therefore necessary to obtain a representative analysis.

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