Figure 3. Coercivity spectra of the ARM and IRM and stepwise IRM acquisition. Four types are identified in this study: Type 1, a steep initial increase in the IRM acquisition curves and a lower coercivity of IRM than of ARM; Type 2, a gradual rise in the IRM acquisition curves and a higher coercivity of IRM than of ARM; Type 3, a relatively steep initial increase in the IRM acquisition curves and a higher coercivity of IRM than of ARM; and Type 4, a steep initial increase in the IRM acquisition curves and similar AF demagnetization curves for IRM and ARM. ARM = anhysteretic remanent magnetization, IRM = isothermal remanent magnetization, SIRM = saturation isothermal remanent magnetization.