“Wasp‐waisted” hysteresis loops from a pyrrhotite and magnetite‐bearing remagnetized Triassic limestone

Remagnetized samples of the Triassic Prezzo Limestone from northern Italy contain a mixture of pyrrhotite and magnetite, as deduced by thermal unblocking characteristics of triaxial isothermal remanent magnetizations (IRM's) and low‐temperature cycling of saturation IRM's. Hysteresis loops are commonly “wasp‐waisted” and remanent coercivity curves contain a break in slope, as a result of the contrast in coercivity between remanence‐carrying pyrrhotite and magnetite. The relative proportion of the high to low remanent coercivity fractions, as deduced by the study of the remanent coercivity curves, seems to control the degree of “wasp‐waistedness” of the hysteresis loops. Samples that are dominated by one of the two coercivity end members have lower Bcr/Bc values as well as hysteresis loops that have a less pronounced constricted waist compared to samples with higher Bcr/Bc values. Maximum Bcr/Bc values (and thus maximum degrees of “wasp‐waistedness” in the hysteresis loops) are attained when the low remanent coercivity fraction contributes 15–35% to the bulk remanent coercivity curves.