PALEOMAGNETIC RESEARCH IN THE USSR Paleomagnetism is a new field of Earth science which lies on the boundary between geophysics, geology, and the study of ferromagnetism. Research in this field is becoming a matter of ever-increasing interest, since it gives us information on the following important subjects: 1) the history of the Earth's magnetic field and the variations in this field throughout geological time; 2) the relation between these field variations and phenomena taking place during the course of the Earth's evolution. In addition to this, paleomagnetic research opens whole new vistas in geological stratigraphy and geochronology.
Paleomagnetic studies are developing with particular intensity in the Soviet Union. In order to coordinate the research in this field, a Paleo magnetism Commission was set up at the Shmidt Institute of Earth Physics early in 1959. This commission, which is a part of the Division of Physics and Mathematics of the USSR Academy of Sciences, periodically holds meetings and conferences at which findings in the field of paleomagnetism are presented.
The Fourth All-Union Conference on Paleomagnetism was held at the Institute of Earth Physics from 31 January to 6 February 1961, with 160 dele gates, representing 60 institutions in 28 cities of the Soviet Union, taking part; 26 scientific reports were read and 20 communications were presented. At the Third All-Union Conference on Paleomagnetism, held the previous year, only 58 delegates from 13 Soviet cities were present. These figures indicate how much the interest of geologists and geophysicists in problems of paleomagnetism has grown in recent years.
The reports dealt with the following general subjects: 1) the magnetic field of the Earth in the past and the correlation between geological strata; 2) the different geological-geophysical conditions under which ferromagnetic rocks are formed; 3) the physical fundamentals of paleomagnetism; 4) reverse magnetization; and 5) instrumentation problems.
The following survey reports were presented at the conference: "The Physical Fundamentals of Paleomagnetism," by G. N. Petrova and B. M. Yanovskii; "Paleomagnetic Studies in Stratigraphy and Geochronology," by A. N. Khramov; "The History of the Geomagnetic Field on the Basis of Paleomagnetic Research," by A. G. Kalashnikov; and "A Review of Modern Geotectonic Theories, Particularly Theories of Horizontal Shifting of the Earth's Crust," by P. N. Kropotkin. The first report was actually two
separate studies in one. In his portion Yanovskii gave a theoretical explanation of the remanent magnetization in certain rock types. He discussed the conditions under which the remanent magnetization changes and also in cases in which, despite a change in the crystal lattice of the rock, the magnetization may be considered to be unchanged.
Petrova's report dealt with the basic principles and the limits of application of all the various laboratory methods for determining the stability of the remanent magnetization of rocks. This subject is a very vital one, since magnetologists cannot as yet distinguish between the primary and secondary magnetization of all rocks. Thus, methods must be worked out for obtaining samples in which the direction of the magnetization is practically unchanged.
Khramov's report was of particular interest to geologists. It presented some results of paleomagnetic studies in stratigraphy and geochronology, and it also pointed out some new applications of paleomagnetic research in stratigraphy, paleogeography, paleoclimatology, and tectonics. In particular, the possibility of constructing a geochronological scale by paleomagnetic methods was considered.
The report of Kalashnikov constituted a first attempt toward generalizing all the various paleomagnetic conclusions concerning the position of the magnetic pole during past geological epochs, according to the data of Soviet and non-Soviet investigators. This report included a composite table, compiled using Soviet data, in which material submitted at the present conference was also used.* The various modern geotectonic theories, in particular the theory of horizontal shifting of the Earth's crust, were discussed in detail by Kropotkin. After considering both the fixed-crust and moving-crust hypotheses, the author concluded that in general the contraction theory is being replaced by theories assuming a moving crust. Kropotkin also noted that geophysical methods (and the magnetic method in particular) make it possible to ascertain the dimensions and the mechanism of the crustal motion, a problem which cannot be solved unambiguously by geological methods alone.