The Sommerodde (Telychian, Silurian) positive carbon isotope excursion: why is its magnitude so variable?

David k. Loydell, Juan Carlos Gutiérrez-Marco, Petr Štorch

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The Sommerodde positive organic carbon isotope excursion (SOCIE), within the Oktavites spiralis graptolite Biozone (Telychian, Silurian), was first identified in the Sommerodde-1 core, Bornholm, Denmark, where it is the largest positive excursion within the Upper Ordovician–lower Silurian part of the core. Other published occurrences of the SOCIE are discussed here, together with new δ13Corg data from the Jabalón River section, Corral de Calatrava, central Spain where the SOCIE is only a very minor positive excursion. Very unusually, the SOCIE is best developed in deeper water settings, contrary to the typical pattern of declining excursion magnitude offshore. In the Sommerodde-1 core (Bornholm), and where it has been tentatively identified in the Vežaičiai-2 core (Lithuania), the SOCIE is developed in pale, organic-poor mudstones. It is considered likely that the SOCIE's magnitude has been enhanced in the Sommerodde-1 core record by a change in organic matter composition in the deep marine environment that did not affect shallower marine environments so significantly.
Thematic collection: This article is part of the Chemical Evolution of the Mid-Paleozoic Earth System and Biotic Response collection available at:
Supplementary material: A table of organic carbon isotope data from the Jabalón River section, Corral de Calatrava, central Spain is available at
Original languageEnglish
JournalJournal of the Geological Society
Early online date3 Aug 2023
Publication statusEarly online - 3 Aug 2023

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