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CSPG Special Publications

Abstract


Intl. Symposium of the Devonian system: Papers, Volume II, 1967
Pages 995-1007
Boundaries and Correlations

The Devonian-Carboniferous Boundary in Eurasia

Bernard Mamet

Abstract

The Devonian-Carboniferous boundary has been the subject of much controversy since the creation of both systems as the boundary is truly transitional; moreover, none of the international conventions has been followed by more than a fraction of stratigraphers.

The present boundary is drawn within the Tournaisian of the type-region and is higher than the Etroeungt in its type: consequently Lower Tournaisian should be regarded as Devonian. As a result the stage, substage and period limits do not coincide. Much confusion exists in the type-area and the same problems arise in Eurasia.

Fortunately, foraminiferal zones for the past decade have been of great help in the disputed interval. Rapid evolution of Endothyridae and Tournayellidae allows recognition of four zones which have been observed in Europe and Asia. These zones are characterized by

a) appearance of the Endothyridae sensu stricto (Quasiendothyra bella and Latiendothyra)

b) appearance of Quasiendothyra communis (Septatournayella rauserae zone pars)

c) acme of Quasiendothyra communis (appearance of Quasiendothyra kobeitusana or Quasiendothyra mirabilis) and

d) extinction of the Quasiendothyridae and outburst of the Tournayellid Chernyshinella.

The first two zones are Upper Famennian in the type-region (Famenne), the third one appears at the base of the Etroeungt Limestone (emend) and the final one is practically coincident with the disappearance of Clymenids (Lower Tn2A).

This zonation has proved to be reliable in different basins of Eurasia. The stratigrapher is therefore in the paradoxical situation of having widespread agreement on the zonation but no agreement whatsoever on the periods and stages.

Should the Devonian-Carboniferous boundary be re-defined, emphasis should be put on weighting the various merits of microfaunal zones (Foraminifera or Conodonts) versus macropaleontological zonations (Goniatites or Brachiopods). Boundaries based on these different phyla are different.

Although no formal relation exists between the concept of stage and period, it would be disastrous for internationally-accepted periods not to coincide with equally internationally-accepted stages. Either the Devonian-Carboniferous boundary should be emended or the Famennian-Tournaisian boundary will have to be readjusted.


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