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doi:10.2204/iodp.proc.317.206.2014

Methods and materials

Shore-based measurements were taken at the paleomagnetic laboratories of the Istituto Nazionale di Geofisica e Vulcanologia in Rome (Italy) and at Otago University (New Zealand). Each of these laboratories is equipped with a 2G Enterprises three-axis direct-current superconducting quantum interference device pass-through superconducting rock magnetometer (manufacturer noise level of 10^–6 A/m) placed in a shielded room and including in-line three-axis degaussing coils for remanence measurement and demagnetization. NRM was measured followed by stepwise alternating field (AF) demagnetization. Samples were measured and demagnetized along the three axes following a protocol that included field strengths progressively increasing in 5 mT increments from 5 to 100 mT for the Otago measured samples (OT) and an adjusted protocol for the Rome (RM) measured samples (4, 8, 13, 17, 21, 25, 30, 35, 40, 45, 50, 60, 80, and 100 mT demagnetization). A small subset of samples was thermally demagnetized to 450°C, but this was restricted to lithified samples from Hole U1352C, which did not have to be contained in plastic cubes. Thermal demagnetization was performed in an ASC oven, located in the low-field laboratory at Otago University, capable of heating specimens up to 800°C (thermal measurements at Rome were discarded due to technical faults). Specimens were stepwise heated at 30°C intervals for 30 min. Orientation and intensity of magnetization were measured on the 2G cryogenic magnetometer after each heating step. Magnetic components were calculated on the orthogonal demagnetization diagrams using a least-squares fitting technique, including the maximum angular deviation (MAD) to better assess quality. Data and plots were analyzed using PuffinPlot software (Lurcock and Wilson, 2012). Magnetic susceptibility was also measured at each step using a Bartington loop sensor in-line with the magnetometer. This measurement monitored alteration of magnetic minerals after heating. To determine Curie temperature, magnetic susceptibility was measured as a function of temperature using a Kappabridge magnetic susceptibility meter with a furnace attachment (model MFK1-FA; Agico Ltd.).

On average, one discrete cubic sample with an effective volume of ~7 cm³ was taken aboard the R/V JOIDES Resolution from each section recovered, with the intent of characterizing the magnetic behavior of the sediments in shore-based laboratories. The lithology is mainly dark gray to greenish gray or olive-gray and mud and sandy mud with lesser shell hash, sand, and muddy sand. For paleomagnetic purposes, the lithology with the finest grain size was usually targeted. Sampling procedure and conventions are described in the “Methods” chapter (Expedition 317 Scientists, 2011b). A total of 765 individual discrete samples were measured and data are reported below.

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