Palaeoclimate perturbations before the Sheinwoodian glaciation: A trigger for extinctiond during the 'Ireviken Event'
Summary, in English
sagitta rhenana Superzone) were studied in detail for their oxygen isotope composition. The Upper Kockelella
ranuliformis and Ozarkodina sagitta rhenana Zones represent the peak interval of the Sheinwoodian positive
δ18Oapatite excursion reflecting the coolest conditions with marine sea–water temperatures decreased by
more than 6 °C in the subtropics. The δ18Oapatite data cover pre- through post-‘Ireviken Event’ strata. The
study includes also material from younger levels up to the late Wenlock Ctenognathodus murchisoni Zone.
However this record is incomplete with one major hiatus reflecting the regression associated with the
Middle Silurian Mulde Event.
The stratigraphic levels of the analyzed conodont samples from Estonia can be correlated with high precision
to the datum points of the ‘Ireviken Event’ strata in the Lower and Upper Visby formations on Gotland,
Sweden. Inferred short-term climatic changes in the upper Telychian part of the studied interval may have
been caused by phases of major volcanic activity along the Caledonian front. Across the ‘Ireviken Event’ we
observe variations in oxygen isotope ratios which allow a direct comparison to the stepwise extinctions and
faunal reorganisations in different groups. Our data suggest that faunal extinctions are connected to time
intervals of warming before the establishment of more stable and cooler conditions during the main
Sheinwoodian glacial. The most severe extinctions and faunal turnovers at datum points 2 and 4 occurred
during the early, warmer interval of the event. After the shift into the Sheinwoodian icehouse in the Lower
Kockelella ranuliformis Zone, reflected by rapidly decreasing sea–water temperatures, faunas restabilized and
reefal communities started to flourish. Sedimentary evidence for the glaciation is discussed for different
Palaeogeography, Palaeoclimatology, Palaeoecology
Artikel i tidskrift
- Oxygen isotopes
- ISSN: 1872-616X