VARIATIONS OF THE GEOMAGNETIC FIELD DURING THE CRETACEOUS
A.Yu. Kurazhkovskiia, N.A. Kurazhkovskayaa, B.I. Klaina, and V.Yu. Braginb
aBorok Geophysical Observatory, Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, Borok, Yaroslavl region, 152742, Russia
bA.A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
Keywords: Cretaceous, paleointensity of geomagnetic field, sedimentary rocks, stratigraphic correlation
Pages: 712-719
Abstract
This study provides a compilation of the paleointensity records for the Cretaceous period derived from sediments of the Russian Plate and adjacent areas. The paleoinetensity values were calibrated using the laboratory redeposition experiments. Remarkable differences in the relative paleointensity variations were detected at the Berriasian-Early Barremian, Late Barremian-Santonian, and Early-Late Maastrichtian boundaries. In the Berriasian-Early Barremian interval, the paleointensity varied stochastically, with the amplitude of about 1 Н 0 and the mean value of 0.63 Н 0 ( Н 0 is the present-day geomagnetic field intensity assumed to be 40 μT). The records for the Barremian-Santonian give a picture of the geomagnetic field with alternating high- and low-amplitude features. The mean paleointensities remain constantly high (being on average 0.87 Н 0), and intervals of low-amplitude variation alternate with the pronounced bursts (3.5 Н 0). The Late Maastrichtian interval is characterized by high-amplitude paleointensity variations (4 Н 0) and a sharp drop toward the end of the interval. All records show remarkable similarities near the boundaries between geological time intervals, which are an increase in the amplitude and mean values of intensity at the end of intervals followed by a decrease toward the beginning of the subsequent interval.
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