Detrital Remanence, Inclination Errors, and Anhysteretic Remanence Anisotropy: Quantitative Model and Experimental Results

SUMMARY We suggest that inclination errors in detrital remanent magnetization (DRM) may be recognized and corrected by measurement of the anisotropy of anhysteretic remanent magnetization (ARM). ARM anisotropy reflects directional variations in the remanence capacity of relatively fine‐grained magnetic particles in rocks or sediments, generally the same particles that carry the stable component of DRM. Relative vertical and horizontal DRM magnitudes are controlled by this directional remanence capacity, as well as by the alignment efficiency of the particle magnetic moments, which in turn is governed by the relative intensities of the vertical and horizontal components of the ambient magnetic field. Thus the respective vertical and horizontal components of palaeointensity, and therefore palaeofield inclination, may be obtained by normalizing the measured DRM components by parallel ARM intensities. Synthetic sediments containing silica, kaolin, and sized magnetite powders have previously been found to acquire experimental DRM with an inclination error that is a direct function of kaolin concentration. Further experiments have now shown that ARM anisotropy in the synthetic sediments is also a direct function of kaolin content, and thus a correlation exists between DRM inclination errors and ARM anisotropy. Multiplying the measured DRM vector by the inverse of the ARM anisotropy matrix yields an improved estimate of the actual laboratory depositional field in all cases. For samples with acicular 0.5 μm magnetite, this procedure reduces a mean inclination error of over 5° to less than 0.5°. Samples with subequant magnetite of slightly larger grain size (0.75 μm) exhibit similar ARM anisotropy (∼10 per cent), but somewhat larger inclination errors (∼10°). We interpret this in terms of stronger horizontal alignment but weaker particle anisotropies for the larger, more equant magnetites.