Stratigraphic scale and geological section

Research subject. The most frequently utilized fundamental notions in stratigraphy are discussed: concrete section, composite section, the stratigraphic scale, the biochronologic scale, the International Stratigraphic Scale.

Materials and methods. The conventional content of these concepts is analyzed. The logical invalidity and negative consequences of the identification of subdivisions of the stratigraphic scale and subdivisions of a section are shown. The study of a section provides a way of obtaining information about the stratigraphic sequence of rock formation and the distribution of evidence of the events included in them, which are necessary for constructing stratigraphic scales. The close connection of the source of the actual data and results of its stratigraphic interpretation is the reason for the traditional identification of the subdivisions of the stratigraphic scale and subdivisions of a particular section.

Results. The biochronologic scale inherits from a section the time sequence of occurrences of species of a certain group of organisms selected as the basis of a scale. However, special features of the evolutionary development of organisms do not depend on the composition of the containing deposits and the method of the separation of sedimentary rock sequences. This development makes it possible during the study of many specific sections to establish homotaxis in the distribution of fossils, i.e., to build a biochronologic scale. Thus, the understanding of the scale is a model of the biochronologic calculation of geological time. Like any model, a scale cannot be identical to what it simulates.

Conclusion. A precise differentiation of the scale and a section is the basis for drawing correct stratigraphic conclusions. A zone is the smallest subdivision of the biostratigraphic scale. Zones are not divided into parts, are discrete (between adjacent zones there are no time passages), equivalent and are characterized by only the place which it occupies on the scale. The construction of a zone scale precedes the establishment of the material equivalent of the zone - of a stratozone - in the section. Any part of a stratozone is dated by the complete zone. The identification of the zonal scale with a sequence of stratozones in the section does not make it possible to understand the minimum dimensionality of a zone subdivision. The International Stratigraphic Scale (ISS) is defined, based on domestic stratigraphic codes and on foreign reference books, as a stratigraphic sequence of rocks (geological bodies) in total volume without passages and overlaps. In this treatment the ISS is not the scale, but is a complete (composite) geological section of the earth’s crust. The biostratigraphic scale serves as a tool of correlation. The ISS gives only the name of that subdivision, with which a concrete section is compared, and the geological age of the deposits of this section is designated by this name.

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