In contrast to stratigraphy, the object of study of which is the temporal correlation of layers and strata distinguished by the stability within certain characteristics and position in the crustal section, the objects of cyclostratigraphy are combinations of layers with directional variability of these characteristics. The main criteria for the temporal limitation of such objects are not the disturbance of the stationarity of the observed characteristics, but the phases corresponding to the change of tendencies in the directional sequence of bedding (transgressive or regressive). Therefore, the task of cyclostratigraphy becomes the search for extreme positions in the sections of sedimentary strata, reflecting the change of tendencies of the transgressive- regressive process. Obviously, the extremums sought for in the content fix the change of trends in the development of one of the three groups of sediment-forming exogenic factors - dynamic, chemical, and climatic.
