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The Cambrian Lower Boundary Problem

Published online by Cambridge University Press:  01 May 2009

A. Yu. Rozanov
Affiliation:
Geological Institute of the Academy of Sciences of the U.S.S.R., Pyzhevsky per., 7, Moscow, U.S.S.R.

Abstract

Based on the study of distribution of assemblages of skeletal organic remains we have established the synchronous appearance of a skeleton in certain fossil groups; this enables us to draw the lower boundary of Cambrian according to the first zone with a certain assemblage of skeletal fossils.

Wide distribution, in sections of various parts of the world, of deposits having no trilobites but containing similar assemblages of other skeletal fossils, has made it possible to distinguish them as an independent Tommotian stage. In Siberian sections this can be subdivided into three zones based on archaeocyathans.

The deposits of the Tommotian stage are underlain by deposits containing no skeletal fossils; in their carbonate composition they are, as a rule, rich in oncolites and catagraphs (algae of uncertain affinities or products of algal activity), and stromatolites of a socalled “Vendian” or “Yudomian” assemblage.

A regular distribution of assemblages of organic remains in the Cambrian-Pre-Cambrian boundary layers point to a leading role for a biostratigraphical method in the solution of the problem of the Cambrian lower boundary.

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Copyright
Copyright © Cambridge University Press 1967

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