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AAPG Bulletin

Abstract


Volume: 50 (1966)

Issue: 3. (March)

First Page: 608

Last Page: 608

Title: Upper Silurian Conodonts from Welsh Borderland: ABSTRACT

Author(s): Charles Collinson, E. C. Druce

Article Type: Meeting abstract

Abstract:

In recent years, correlation of the Silurian-Devonian boundary from its type section with areas outside Britain has been the subject of considerable discussion accompanied by some opinion favoring transfer of the Silurian standard to the European mainland. Difficulty arises partly because the boundary in Britain is placed at a pronounced facies change and partly because zonal graptolites, which are widely used to correlate the Silurian in continental Europe and elsewhere, occur in Britain no higher than the middle of the Ludlow. A most significant advance toward clarifying the situation was made in 1964 by Walliser, who published a detailed conodont zonal succession from the Silurian of the Carnic Alps of Austria and related it to the standard graptolite zones in Bohemia nd Germany.

In 1963, the authors collected 50 pounds of calcareous siltstone from the upper part of the Whitcliffe Flags at Diddlebury, 6 miles north of Ludlow in Shropshire, and acidized it in order to recover the conodonts present. The 850 specimens that were extracted clearly refer the fauna to Walliser's uppermost Silurian conodont zone, the eosteinhornensis zone. This reference indicates that the top of the Ludlovian Series correlates essentially with the top of the Bohemian Budnany (E-beta-two) and implies that the Ludlow and Budnany are approximately equivalent. In terms of graptolite zones, the Silurian-Devonian boundary should occur at the base of the Monograptus uniformis zone inasmuch as it marks the upper limit of Walliser's eosteinhornensis zone. Walliser, who has studied eosteinhorn nsis-zone conodonts from other localities in Britain, proposes that the Silurian-Devonian boundary in continental Europe be fixed by the earliest occurrence of Monograptus uniformis. In this context, the Skala Formation of Podolia (Russia) is essentially late Ludlovian in age as are the Calcaire de Lievin of northern France and the Untere Steinhorn-Schichten of the German Kellerwald.

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Copyright 1997 American Association of Petroleum Geologists