On the possibility of application of cyclostratigraphic analysis in study of the duration of magnetic polarity zones in the sediments of the Katav Formation (Upper Riphean, Southern Urals)
The paper presents the preliminary results of a cyclostratigraphic study of three sections of the Katav Formation in the Southern Urals, conducted in parallel with the detailed construction of the geomagnetic polarity scale, which made it possible to estimate the average sedimentation rate and the number of geomagnetic field inversions for a fairly certain time interval. The spectral analysis of changes in the magnetic susceptibility along the section makes it possible to distinguish distinct peaks on the periodogram, which are compared with orbital cycles. Based on the identified Milankovitch cycles, the accumulation duration of the studied part of the section of the Katav Formation and the average duration of one magnetozone are estimated. The analysis of the spectra of variations in magnetic susceptibility was performed using the “multi-taper” method; peaks were detected at frequencies close to those predicted for orbital cycles at the Precambrian/Paleozoic boundary. According to the results obtained, the average sedimentation rate of rocks of the Katav Formation in the studied sections is 0.04-0.05 m/kyr, and the maximum duration of accumulation of sediments with a thickness of 200 m is about 5 million years. If we take into account that several tens of magnetic zones of direct and reverse magnetic polarity are known in the deposits of the Katav Formation, the average duration of a single magnetic zone is estimated at 51.5 kyr, which is comparable to the data of the Zigan Formation of the Upper Vendian, the deposits of which are considered unique in terms of inversion frequency. The results obtained indicate once again the possible existence of the anomalous (hyperactive) state of the geomagnetic field in the Late Precambrian and at the Precambrian/Paleozoic boundary. According to the results of research, a more detailed magnetostratigraphic and cyclostratigraphic study of the sections of the Katav Formation is recommended for a more reasonable estimate of the sedimentation rate and duration of the magnetozone in order to test the hypothesis of ultrahigh frequency of inversions.