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However, these isotopic techniques are limited by the potential changes in growth rates, the half-lives, and by the difficulty in determining sample thickness, all of which could potentially result in large dating errors.Palaeomagnetism is an alternative method of dating Fe-Mn crusts, which can provide a high-resolution time framework by correlating the polarity reversal pattern retrieved from a sample with a reference geomagnetic time scale (GPTS) described the first measurements of the natural remanent magnetization (NRM) of Fe-Mn nodules and demonstrated that they preserved a record of geomagnetic polarity reversals.The map was generated with Geo Map App, (B–F) Photographs of the sample and slice. They were collected from the Pacific Ocean (PO-01, 20°19′N, 174°10′E, water depth of 2355 m), the Indian Ocean (IO-01, 37°47′S, 49°45′E, water depth of 2576 m) and the South China Sea (SCS-01: 15°17′N, 117°34′E, water depth of 3273 m; and SCS-02: 15°09′N, 117°23′E, water depth of 2430 m) with no growth hiatuses (see Fig. In all cases, the substrate rock and the smooth aspect of the upper surface were used to determine the growth direction (Fig. Subsamples of Fe-Mn crusts were cut with a new low-speed diamond wire cutting machine (Model STX-202A) (Fig. The wire diameter is only 0.20 mm, which considerably reduced the amount of material lost during cutting.The thickness lost during cutting needs to be estimated when calculating the growth rate.Thus, it is important to investigate the palaeoceanographic conditions in which the Fe-Mn crusts formed in these oceanic areas.During recent research cruises, we obtained Fe-Mn crusts from the Pacific and Indian Oceans and the South China Sea.Due to their continuous and extremely slow growth rate (typically several millimetres per million years), Fe-Mn crusts provide a record of the regional and global long-term environmental variations based on temporal changes in radiogenic isotope geochemistry (e.g., Pb, Sr, Nd, Os, Hf), the stable isotope composition of metals (e.g., Fe, Zn, Ni, Cd, Cu, Tl, Mo), and trace metal element distributions.Fine-scale analyses are clearly important for correlating the geochemistry of crusts with palaeoceanographic events.
1A) using a new type of low-speed diamond wire cutting machine (Model STX-202A, Shenyang Kejing Auto-instrument Co., Ltd.) to obtain sample slice thicknesses of less than 1.0 mm.
The magnetostratigraphic framework, established via correlation with the Geomagnetic Polarity Time Scale 2012, implies growth rates of 4.82 mm/Ma, 4.95 mm/Ma, 4.48 mm/Ma and 11.28 mm/Ma for samples PO-01, SCS-01, SCS-02 and IO-01, respectively.
Rock magnetic measurements revealed that the Fe-Mn crust samples from the Pacific Ocean and Indian Ocean were dominated by low coercivity, non-interacting, single-domain (SD) magnetite particles, whereas the South China Sea samples were dominated by SD/pseudo-single-domain (PSD) particles.
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.