Fig. 9
a The NRM intensity is plotted as a function of the IRM intensity. Diagonal lines indicate IRM/NRM ratios of 1, 0.1, 0.01, and 0.001, respectively. Vertical and horizontal grey lines indicate 4 × 10−12 Am2 intensity lines (detection limit). The sample with M IRM < 4 × 10−10 Am2 or M NRM < 4 × 10−12 Am2 are shown as grey symbols. b The NRM/IRM ratio is plotted as a function of B c . c The LTD memory of IRM is plotted as a function of the NRM/IRM ratio. The SD- and PSD-like samples are plotted as red and blue symbols, respectively (see Fig. 5). The selected samples are shown as inverted triangle, diamond, triangle, and square symbols (see Fig. 6)