SECULAR VARIATION OF THE GEOMAGNETIC-FIELD - DATA FROM THE VARVED CLAYS OF SOVIET KARELIA

In the territory of Soviet Karelia (62°N, 34°E) a paleomagnetic study of varved clays at six sections, situated in the north of Lake Ladoga and in the west and east of Lake Onega, has been carried out. The sections are located in different zones of deglaciation and overlap in age. They cover the time interval from 16 000 to 10 200 years BP. The sediment age has been defined from varvometric data, palynological and radiocarbon analyses as well as from the information about geological and geomorphological development of the region. The laboratory study reveals that considerable paleomagnetic information can be obtained from the varved clays. Geochronological and paleomagnetic studies have been carried out for each section. The geomagnetic origin for the variations of magnetic properties (declination, inclination) has been demonstrated. The result of these studies is presented in a magnetochronological plot of declination and inclination variations for the northwest territory of European U.S.S.R. in the time interval 16 000-10 200 years BP. Maximum amplitude of the declination variation reached 70° (∼ 12 000 years BP); inclination variation is 50% smaller. The characteristic periods for declination are 800, 1750, 2100-2200 and 2500 years, and for inclination 900, 1750-1850, 2600-2700 years, respectively, as obtained by spectral analysis. The virtual geomagnetic pole (VGP) moves both clockwise and counter-clockwise: the latter is generally predominant. VGP does not reach values lower than 60°N. The detailed curves of declination and inclination can be used for regional magnetostratigraphic studies and for correlation of sediments in adjacent regions such as Finland and Sweden. © 1990.