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doi:10.2204/iodp.proc.342.207.2018

Methods and materials

U-channel samples (typically 1.5 m in length with a 2 cm × 2 cm cross section) were taken from the central part of the archive-half cores along the stratigraphic splice described in the “Expedition 342 summary” chapter (Norris et al., 2014a): 30–160 m core composite depth below seafloor (CCSF) for Site U1403, 18–166 m CCSF for Site U1408, 6–142 m CCSF for Site U1409, and 0–165 m CCSF for Site U1410. A total of 530 samples were collected from archive halves, and 133 samples were collected from working halves. All samples were taken from intervals recovered using the advanced piston corer (APC) system. The samples were collected during February 2013 and March 2014 at the IODP Bremen Core Repository (Bremen, Germany). We conducted progressive AF demagnetizations on NRMs of the samples up to 80 mT in approximately 10–12 treatment steps. The remanence was measured at each AF step at a stratigraphic resolution of 1 cm. The 0–20 mT demagnetization steps were omitted for archive-half samples because they were already demagnetized during the expedition.

Discrete samples of 7 cm³ cubes were collected during Expedition 342 every few meters along the working-half cores of Hole A at each site. These samples were also AF demagnetized up to 20 mT to construct the shipboard magnetostratigraphy. To further constrain some of the chron boundaries in intervals recovered with the extended core barrel (XCB) system, the samples collected from 210 to 252 m CCSF (Site U1408) and 154 to 294 m CCSF (Site U1410) were subjected to additional progressive AF demagnetization from 20 to 80 mT in 16–18 steps.

All of the shore-based measurements were conducted using a cryogenic magnetometer with an in-line static AF demagnetizer (2G Enterprises model 760R) at the Center for Advanced Marine Core Research, Kochi University. This magnetometer has a response function (single peaks with their full widths at half maxima) of 46 mm (X and Y) and 54 mm (Z) (Oda et al., 2016), and measurement results are smoothed according to the function.

Characteristic remanent magnetization (ChRM) directions for discrete samples and at 1 cm intervals for the U-channel samples were calculated using principal component analysis (PCA; Kirschvink, 1980). No attempt was made to deconvolve the U-channel magnetic data (cf. Oda and Shibuya, 1996; Jackson et al., 2010; Oda and Xuan, 2014). Data from the top and bottom 5 cm of the U-channel samples and from disturbed intervals described in the expedition 342 site reports and observed in core photos were eliminated from the analysis (see the “Methods” chapter [Norris et al., 2014b]). We use the splice tables from the “Site U1403” chapter (Norris et al., 2014c) for Site U1403, by Hull et al. (2017) for Sites U1408 and U1409, and by Boulila et al. (2018) for Site U1410 to plot our data on a composite depth scale (CCSF).

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