Abstract

Crinoids occur in the territory of the USSR in almost all regions where normal Devonian marine sediments are present. Most frequently they are represented by fragmentary remains of columns, arms, and cups, the last comparatively rare. For general biostratigraphic purposes it is usually necessary to rely upon joints and columns. Various artificial schemes of classification of these have been proposed, but these must be regarded as temporary measures prior to the establishment of proper taxonomic categories. The purpose of this classification is to render fragmentary remains of crinoid columns useful as indicators of geologic time.

The study of crinoids (calices, as well as joints and columns) permits the discrimination of three distinct crinoid assemblages in the Early Devonian of the southwestern margin of the Kuznetsk basin, and one in Mountain Altai and in the Far East. All of these assemblages are diagnostic of certain stratigraphic units. In addition a number of assemblages may be distinguished in Middle and Late Devonian sequences of several regions in Siberia.

Detailed studies (mainly on the basis of data from the Altai-Sayan region) of crinoids existing throughout the Devonian Period allows the definition of four stages of relative abundance with corresponding intervals of relative decline.

The investigations show that fragmentary remains of crinoid columns are important stratigraphically.