The role of water content in the magnetization of sediments

Abstract

We have developed a new experimental procedure in order to study the role of water content in the acquisition of post‐depositional detrital remanent magnetism by a sediment. The procedure leads to the determination of the magnetic direction recorded by a sediment as a function of the water content present when that sediment experiences a change in the direction of an applied magnetic field. Experiments with a variety of sediments indicate that in most cases, regardless of the water content, the sediment does not become remagnetized. Such behavior requires a re‐assessment of the importance of the theoretical notion that at high water contents the magnetic carriers remain mobile within fluid‐filled voids and hence are able to realign along a new applied field. Analysis of the magnetic properties of sediment samples initially stirred in zero and non‐zero magnetic fields leads to the conclusion that the magnetization of the sediments may arise from small‐scale, shear‐induced liquefaction.

How does Chinese loess become magnetized?

“…The samples were measured in the magnetometer again and were weighed again to allow calculation of the water content. Water content was estimated following the definition of Verosub et al (1979) where: H 2 O% = ((Mass total -Mass dry )/Mass dry ) x 100%. In many cases, water ponded above the sediment surface in the plastic cubes used to hold the samples, so H 2 O% is not a true measure of water content in relation to sediment pore space.…”

“…The NRM/ARM ratio for such samples is low (~0.1-0.2) because of the inefficient alignment of magnetic particles (Figure 4.8d). As discussed above, the water content definition of Verosub et al (1979) is not a true measure of water content in relation to sediment pore space; the high H 2 O% values indicate that the sample was a wet slurry. Despite this definition, there is a key change in the magnetic recording quality at H 2 O% = 40-50%.…”

Deconvolution Method for Directions of the Post-Depositional Detrital Remanent Magnetization Using an Exponential Fixing Function.

“…The sediments redeposited in the laboratory sometimes show that the amount of remagnetization gradually decreases in drying (Verosub et al, 1979;Barton et al, 1980;Payne and Verosub, 1982). The redeposition experiments of synthetic and natural sediments by Hamano (1980) indicated that magnetic particles are locked also during the compaction and result in the growth of the post-depositional DRM.…”

“…Verosub (1977) attempted to elucidate the natural state of the DRM by applying a constraint of the critical water content and by taking account of physical processes of the bioturbation and gravitational compaction. According to the experiment by Verosub et al (1979), remagnetization after the deposition, namely the post-depositional DRM, takes place only for a water content higher than a critical value, but stirring the sediment like the bioturbation can generate remagnetization of the sample. Barton and McElhinny (1979) and Barton et al (1980) support this conclusion from their experiments.…”

Role of magnetic interaction in sediments.

“…Recent studies on the acquisition mechanism of the remanences in sediments have revealed the importance of the post-depositional process on though the relative importance of the process depends on the sediment properties (BLOW and HAMILTON, 1978;VEROSUB et al, 1979;BARTON and MCELHINNY, 1979). The effect of the particle interaction is much more important in the postdepositional process than in the process while the particles are floating in water.…”