RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 7, ES3003, doi:10.2205/2005ES000175, 2005

Introduction

[2]  The geomagnetic field reversals seem to be among the most interesting phenomena discovered by the science in the 20th century. Naturally, the process of their operation attracted the attention of geoscientists who began to study them at the end of the 1950s to the beginning of the 1960s [Momose, 1958; Nomura, 1963; Petrova and Rybak, 1963; Sigurgeirsson, 1957; Van Zijl et al., 1962]. The characteristics of the geomagnetic field during its reversals, that is, during its transitions from one polarity to another, were and still are of great interest to the geoscientists, because the phenomenology of the processes of the destruction and reconstruction of the stationary magnetic moment, apparently reflecting the characteristics of the processes that violate the mechanism of its generation and reconstruction, might provide information for the operation of the dynamo mechanism, might help to understand its physical essence and broaden our knowledge about the structure of the Earth's deep envelopes, and of the processes operating in them in the scale of geological time. Moreover, the discovery of the fact that each individual inversion has its own distinctive features which can be used to recognize it in the paleomagnetic rock sequences, would increase the value of the magnetostratigraphic scale. The second line of research did not give the expected results: inversions turned out to be indistinguishable in terms of the patterns of their operations, which are necessary for using them in stratigraphic studies. Yet, the work done in this line of research resulted in the collection of information which is of great interest for developing a generation theory and verifying its fundamental positions.

[3]  The accumulation of data for transitional conditions is a slow process: the detailed records of the polarity reversal process are found rather rarely. Moreover, the correct interpretation of the results calls for the detailed study of not only the transitional interval itself, but also of the adjacent stationary intervals. The latter circumstance was not taken into consideration immediately by the researchers engaged in the studies concerned. Another important circumstance was associated with the fact that studies of this kind called for a significantly larger volume of work. This is especially obvious for the studies of transitional zones in sedimentary rocks, with the high rates of their accumulation. The data available for these zones allow one to characterize the transitional-state field in a required detail.

[4]  Naturally, the records of the magnetic field characteristics, which had been imprinted in sedimentary rocks during the magnetic field inversions, contain a great number of discrepancies. The most substantial of them is the potential smoothing (distortion) of the record owing to the different ages of the sedimentation and postsedimentation components of the orientation magnetization and to the presence of some secondary chemical component with the same carrier of these components of natural remanent magnetization (NRM). This problem was discussed in detail by many researchers [Bolshakov, 1995; Khramov, 1986; Kok and Tauxe, 1996a, 1996b; Langereis et al., 1992; Quidelleur and Valet, 1994; Rochette, 1990; Tauxe, 1993], to name but a few. In his paper, Rochette [1990] suggests the lowest sedimentation rate of the rocks, suitable for studying transitional conditions, to be 5 cm for 1000 years. At the same time, the use of the modern techniques of laboratory paleomagnetic studies allows one to obtain data that in many cases most truly reflect the real characteristics of the inverted field.

[5]  As more data were accumulated for the transitional conditions, repeated attempts were undertaken to generalize and interpret them. Naturally, the main features of the transitional conditions did not change from one generalization to another, but acquired a more detailed pattern with the growing certainty of the conclusions. Yet, the interpretation of these regular characteristics underwent substantial changes.

[6]  Inversions begin with the decline of the magnetic moment ( M ). At the background of the lowered magnetic moment the virtual geomagnetic poles (VGP) happen to reside at the intermediate and low latitudes, where the successive changes in their positions show both a normal and a chaotic character, moving later to the high latitudes of the opposite hemisphere. The magnetic moment grows to its stationary value.

[7]  Although this schematic pattern is basically correct, many of its aspects call for a more detailed description and discussion, which should be based on the data obtained in the course of studying sedimentary rocks using the results obtained during the last several years.


RJES

Citation: Gurarii, G. Z. (2005), Geomagnetic field reversals: Main results and basic problems, Russ. J. Earth Sci., 7, ES3003, doi:10.2205/2005ES000175.

Copyright 2005 by the Russian Journal of Earth Sciences

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