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Mikael Calner

Mikael Calner

Professor

Mikael Calner

Palaeoclimate perturbations before the Sheinwoodian glaciation: A trigger for extinctiond during the 'Ireviken Event'

Författare

  • Oliver Lehnert
  • Peep Männik
  • Michael M. Joachimski
  • Mikael Calner
  • Jiri Fryda

Summary, in English

Telychian to Sheinwoodian conodonts (Pterospathodus eopennatus ssp. n. 1 Zone through the Ozarkodina

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

palaeolatitudes.

Avdelning/ar

  • Berggrundsgeologi

Publiceringsår

2010

Språk

Engelska

Sidor

320-331

Publikation/Tidskrift/Serie

Palaeogeography, Palaeoclimatology, Palaeoecology

Volym

296

Issue

3-4

Dokumenttyp

Artikel i tidskrift

Förlag

Elsevier

Ämne

  • Geology

Nyckelord

  • Glaciation
  • Palaeoclimate
  • Oxygen isotopes
  • Silurian
  • Baltoscandia
  • Estonia

Status

Published

ISBN/ISSN/Övrigt

  • ISSN: 1872-616X