Russian Journal of Earth Sciences
Vol. 5, No. 6, December 2003
New paleomagnetic data for the Hauterivian-Aptian deposits of the
Middle Volga region: A possibility of global correlation and dating of
time-shifting of stratigraphic boundaries
A. Yu. Guzhikov, E. Yu. Baraboshkin, and A. V. Birbina
Abstract
The aim of this project was to study the paleomagnetic
stratigraphy of the Hauterivian-Aptian deposits in the Middle
Volga region, namely in the areas of the Saratov, Samara, and
Uliyanovsk right-hand Volga areas. Original data were obtained
for the first time for the magnetic polarity of the Hauterivian
and Barrhemian rocks of the Russian Platform. The results
obtained for the Aptian rocks agree very well with the results
of the previous paleomagnetic studies which had been carried out
in the Uliyanovsk region earlier
[Baraboshkin et al., 1999]
and in the vicinities of Saratov City
[Grishanov, 1984].
Based on the complex correlation of the bio- and magnetostratigraphic
data for the rocks from the Middle Volga region, the North
Caucasus, the North Mediterranean area, and South England, it is
shown that the stage and substage boundaries of the Hauterivian,
Barrhemian, and Aptian stages differ in terms of the absolute age
from the similar boundaries in the Boreal Belt by a value of
some 105 -106 years, which is comparable with the duration of
the Early Cretaceous ammonite zones. The diachronism of the
Lower Aptian ammonite zones (Deshayesites volgensis - D.
forbesi) and of the Middle Aptian Parahoplites melchioris zone
in different regions. The results of this study called for a
complex substantiation and tracing of the units of the General
Stratigraphic Scale (GSS). The basic GSS unit must be a stage,
rather than a zone, because where boundaries were traced over a
large territory, the asynchronism of the boundaries between the
zones is comparable with the duration of the zones, whereas in
the case of a stage it is 1-2 orders of magnitude lower.
Geomagnetic inversions or isotopic data can be used to test the
isochronism of stratigraphic boundaries.