Elena IsupovaA Study of Large-Square Sediments

Studies of magnetism of sedimentary rocks often reveal an inclination error (dI ) of the orientational remanent magnetization (Jro) direction, inclination Io being lower than the inclination of sedimentation field IH .
To study the inclination error, a large-square artificial sediment has been produced. The plastic container with horizontal size of 20 x 25 cm and 20 cm in height was used as a sedimentation vessel. As a deposition material, a mixture of non-magnetic blue Proterozoic clay, chalk powder and magnetite particles (0.5 to about 30 micrometers in size) was used; magnetite content was 0.7% by weight. Cubic samples have been cut from the dried sediment according to scheme 7 x 8: 8 rows, 7 samples in each row.
Several techniques to correct an inclination error exist, due to King, Belokon' and Novoselov. However, all these techniques are not able to correct inclination errors completely. We have proposed a new technique based on a slightly modified Novoselov method. The Novoselov method is based on a hypothesis of a formation of an additional horizontal remanence component Jrx, its nature not being specified. Our technique is based upon an assumption that Jrx formation is a result of reducing a Jro vertical component during sedimentation.
Following results have been obtained from the experimental study of our sediment:

         The Jo value averaged over the whole sediment was 68. The average dI was 11.

         When using King technique, the inclination error was corrected by 2 on average.

         With Novoselov method the inclination error was "overcorrected" by about 40.

         With our method the inclination error was corrected by 8, yielding an inclination fairly close to that of the sedimentation field.

Moreover, we have noticed that vertical anisotropy axes of different specimens  are not truly vertical,  their directions deviating by up to 10 from the vertical.


E.V. Isupova, P.V. Dubrovin, V.A. Shashkanov, I.N. Petrov

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