Fig. 5.

Micromagnetic simulations of magnetofossils for samples from ODP Hole 1263C. a–c Micromagnetic simulation of FORC diagrams for PETM onset sample: a geometry, b simulated FORCs, and c processed FORC diagram. For input models, particle size distributions of biogenic magnetite are from TEM observations (Fig. 4). The magnetosome chain configurations modelled in c are: 5 crystals in a chain, 60 chains, a chain bending factor of 0.5, a grain separation of 20 nm, and randomly oriented chains with packing fraction of 0.001 (ref. ⁴⁴). d–f Micromagnetic simulation of FORC diagrams for the three PETM samples using model parameters: 10 crystals in a chain, a chain bending factor of 1.0 (collapsed chains) and a grain separation of 20 nm. The three simulations represent the samples for which experimental results are presented in Figs. 2 and 4. For all FORC simulations, we modelled 100 FORCs with B_c= 160 mT, B_u= 60 mT, and averaged 100 identical FORC simulations. Particles were selected randomly again from the TEM observations for each FORC simulation. FORC diagrams were processed using FORCinel⁶⁷ with VARIFORC smoothing parameters:⁶⁸ {s_c0, s_c1, s_b0, s_b1, λ_c, λ_b} = {7, 7, 2, 7, 0.1, 0.1}. g, h Back field coercivity distributions extracted from the simulated FORC diagrams in d–f for the three PETM samples. h Data from the enlarged dashed box in g; the arrow in h indicates the data trend