A large number of Lower Silurian (Llandovery) K-bentonite
beds have been recorded from
northwestern Europe, particularly in Baltoscandia and the
British Isles, but previous attempts to trace single
beds regionally have yielded inconclusive results. The
present study suggests that based on its unusual
thickness, stratigraphic position and trace element
geochemistry, one Telychian ash bed, the Osmundsberg
K-bentonite, can be recognized at many localities in Estonia,
Sweden and Norway and probably also in
Scotland and Northern Ireland. This bed, which is up to 115 cm
thick, is in the lower–middle turriculatus
Zone. The stratigraphic position, thickness variation and
geographic distribution of the Osmundsberg
K-bentonite are illustrated by means of 12 selected Llandovery
successions in Sweden, Estonia, Norway,
Denmark, Scotland and Northern Ireland. In Baltoscandia, the
Osmundsberg K-bentonite shows a trend of
general thickness increase in a western direction suggesting
that its source area was located in the northern
Iapetus region between Baltica and Laurentia. Because
large-magnitude ash falls like the one that produced
the Osmundsberg K-bentonite last at most a few weeks, such an
ash bed may be used as a unique time-plane
for a variety of regional geological and palaeontological studies.