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doi:10.2204/iodp.proc.313.201.2014

Methods and materials

Premeasurement treatment of sediment samples

Siliciclastic sediments drilled from three sites of Expedition 313 on the New Jersey shallow shelf (Fig. F1) often include biogenic materials (e.g., organic matter and calcareous and siliceous biogenic skeletons such as foraminifers, nannoplankton, radiolarians, diatoms, etc.). Before analyzing the sediment grain size, all organic materials were dissolved using the particle degradation treatment described below.

After drying a subsample of 5–8 g taken from each 20 cm³ or 10 g of sediment, it was first degraded into particles through pounding semisolid parts softly and carefully in an agate mortar using a pestle. To dissolve organic material, the sediment sample first soaked in 5–8 cm³ of 0.1 M H₂O₂ solution in a test tube for a day at room temperature. After adding 3–6 cm³ of 0.1 M H₂O₂, the tube was then kept in a shaking water bath for 1 h at 30°C and a 100 rpm shaking rate. Following shaking, the sample was kept in a warm water bath at 50°C for 1 day. After cooling to ambient temperature, the tube was filled by adding distilled water and centrifuged for 1 h at 3400 rpm. After removing the upper clean layer and adding distilled water, the sediment was centrifuged twice more. The sediment was then dried for a few days in a thermostatic oven. As a last procedure the sediment was again degraded into particles by softly and carefully pounding semisolid parts, using a pestle in an agate mortar. Ultrasonic vibration for particle degradation was not used in order to avoid particle breakage.

Measurement

We used two analyzers installed at the Geological Survey of Japan, the LA-300 for silt-sized sediments finer than fine sand and the CAMSIZER for sand-sized sediments, both of which are made by Horiba Co. Ltd. (www.horiba.com/). The LA-300 is a laser scattering particle-size distribution analyzer with a measurable size range from 0.1 to 600 µm. Electrical signals corresponding to the intensity of the scattered light are used to calculate the size distribution of particles, based on the Mie scattering theory. In this study, we measured sediment samples under a relative refraction index as 120-001i. After adjustment of the optical axis, samples were put into a dispersion medium chamber and measured with a laser light transmission rate of 85%–90%. A data set of each measurement is divided into 64 logarithmically equally spaced classes between 0.1 and 600 µm. The installed software calculates major statistical parameters.

A particle analyzer with digital image processing (CAMSIZER) uses two digital (CCD) cameras for the measurable range from 30 µm to 30 mm. A data set of each measurement is divided into 40 logarithmically equally spaced classes between –3.0 and 6.0 ϕ with intervals of 0.2 ϕ. Using Microsoft Excel software, four major statistical parameters were calculated.

Tables T1, T2, and T3 show four statistical parameters such as mean, median, mode of grain size, and standard deviation for each sample measurement.

Materials

A total of 275 sediment samples were measured from the three sites. The measurable horizons at the three sites are approximately within the unconsolidated upper half of the drilled sections, representing thickness ranges of 293, 177, and 164 m at Sites M0027, M0028, and M0029, respectively, and a total of 634 m.

Site M0027

A total of 135 unconsolidated sediment samples suitable for measurements were obtained from Cores 313-M0027A-66X (195 meters composite depth [mcd]) to 170R (489 mcd) (293 m thick). Consolidated sediments abundant in authigenic glaucony (glauconite) grains were unfit for analysis from depths below Core 171R and so were the poorly recoverable horizons above Core 65X.

In general, we took one sample from each core in the silt-sized sediment intervals and from each section in the sand-sized sediments, except for horizons disturbed during drilling or core splitting. Of the 135 samples, 99 came from muddy to very fine sandy sediments that were measured using the LA-300, whereas 36 samples from fine to coarse sandy sediments were measured using the CAMSIZER.

Site M0028

At Site M0028, we selected a total of 80 samples from unconsolidated and well-recovered intervals of Cores 313-M0028A-14R to 38R (257–323 mcd; 66 m) and 79R to 114R (412–523 mcd; 111 m). We generally took one sample from each core except for the horizons disturbed during drilling or core splitting. The interval between Cores 39R and 78R (323–412 mcd) is heterogeneously consolidated and poorly recovered at large. Among 80 samples, 73 were measured by the LA-300 and the others were measured by the CAMSIZER.

Site M0029

At Site M0029, a total of 60 samples were selected from unconsolidated intervals of Cores 313-M0029A-50R to 84R (280–379 mcd; 99 m) and 111R to 133R (457–522 mcd; 65 m). We generally took one sample from each core. Twelve sand-sized sediments were measured by the CAMSIZER and the rest were measured by the LA-300.

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