Permian Stratigraphic Record of the Volga–Kama Region: Cyclic and Fractal Properties

Abstract

In this paper, we investigate aspects of Permian cyclostratigraphy of the Volga–Kama region in the eastern part of the Russian Plate. Analysis of geological data was based on cyclic and fractal properties of the stratigraphic record. Data on important sedimentary characteristics such as grain size composition, magnetic susceptibility, and carbonate content were analysed using maximum entropy and Fourier methods. Variations of coarse- and fine-grained contents and magnetic susceptibility were found to be the major and secondary factors, respectively, forming sedimentary cycles in outcrops of Biarmian and Tatarian deposits along the banks of the Kama and Volga rivers. The grain size composition as a cyclic response was also revealed in subsurface sections based on gamma-ray log Fourier spectra in the Volga–Kama interfluvial area. Milankovitch cycles are able to be distinguished in the summarized spectra of the maximum entropy method. Log–log plots of cycle thicknesses, sedimentation rates, and ages point to the fractal nature of the investigated stratigraphic record. Interpretation of fractal properties on a Cantor set model and a Hurst exponent model allow characterization of the estimated time scales and completeness of the stratigraphic record, which shows many breaks in the sedimentary history of the Biarmian and Tatarian.