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The slices must be cut perpendicular to the growth axis, and the relative orientation of each slice must be determined.The following sliced samples were obtained: 31 slices with dimensions of 15.5 mm × 14.5 mm × 1.0–1.5 mm from sample PO-01 from the Northwest Pacific, 9 slices with dimensions of 11 mm × 11 mm × 1.0–1.5 mm from sample SCS-01 from the South China Sea, 17 slices with dimensions of 16 mm × 16 mm × 0.4–0.7 mm from sample SCS-02 from the South China Sea, and 15 slices with dimensions of 12 mm × 14 mm × 0.5–0.8 mm from sample IO-01 from the Southwest Indian Ridge.The use of this very fine saw to obtain samples of Fe-Mn crusts with thicknesses of less than 1.0 mm is a major advance of this study and yielded reliable and repeatable paleomagnetic measurements with a SQUID magnetometer in a conventional paleomagnetic laboratory.Isothermal remanent magnetization (IRM) experiments reveal coercivity (Bcr) values within the range of 20–30 m T, which are compatible with a soft, ferromagnetic component such as magnetite (Fig. Variations in the magnetic susceptibility with temperature (κ-T curves) for the four crust samples are shown in Fig. For samples used in this study, both the heating and cooling curves exhibited an obvious Curie temperature of approximately 580 °C indicating magnetite.Thus, it is important to investigate the palaeoceanographic conditions in which the Fe-Mn crusts formed in these oceanic areas.

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For this reason, it has been very difficult to prepare suitable samples for traditional SQUID magnetometer measurements and subsequently establish a geochronological framework for Fe-Mn crusts.The growth dates and ages of Fe-Mn crusts have been determined primarily using U-Th-series isotopes (the .In addition, Os isotope stratigraphy has been successfully applied to Fe-Mn crusts, which compares the Os isotope ratios of samples with those that define a Cenozoic seawater curve (crusts as old as 70 Ma can be dated).With samples of this thickness, we could conduct paleomagnetic measurements using a SQUID magnetometer in a conventional paleomagnetic laboratory.In addition to establishing a chronostratigraphic framework, we also determined the composition and grain-size of the magnetic minerals of the hydrogenetic Fe-Mn crusts.(A) Location of the sampling sites in the Pacific (PO-01), South China Sea (SCS-01 and SCS-02) and Southwest Indian Ridge (IO-01). The Pacific sample was collected during the DY34-II cruise; the Indian Ocean sample was collected during the DY115–18 cruise; and the South China Sea samples were collected on the research vessel ‘Haiyangsihao’ during regional surveys of the South China Sea in 2014.