Figure F10. Plots of demagnetization of natural remanent magnetization (NRM), anhysteretic remanent magnetization (ARM), and isothermal remanent magnetization (IRM) and of the acquisition of IRM (IRM ACQ). A. Sample 182-1126B-1H-7, 6-8 cm. B. Sample 182-1126B-19H-3, 59-61 cm. C. Sample 182-1126D-11R-1, 14-16 cm. D. Sample 182-1126D-33R-1, 58-60 cm. The plots summarize the magnetic characteristics of the samples. The acquisition of IRM illustrated in B, C, and D is consistent with the presence of fine magnetite, although that in A demands in addition the presence of another phase that is magnetically harder. The demagnetization plots of NRM demonstrate that the sample in A is within the noise limit of the instrument, whereas the others are resolvable. The ratios of IRM:ARM in B and C are indicative of single-domain behavior and suggest a magnetotactic origin of the magnetite.