Conodont biostratigraphy and carbon isotope stratigraphy of the Middle Ordovician (Darriwilian) Komstad Limestone, southern Sweden

Abstract

The Komstad Limestone forms a distal part of the widespread ‘orthoceratite limestone’ of the Baltoscandian continent. In this paper, we present an integrated conodont biostratigraphy and carbon isotope stratigraphy for a major part of this formation and address its significance for evaluating Middle Ordovician correlation and overall stratigraphy. Four conodont zones are distinguished, including the Lenodus antivariabilis Zone, Lenodus variabilis Zone, the Yangtzeplacognathus crassus Zone, and the Eoplacognathus pseudoplanus Zone. Carbon isotopes have previously not been published from the Komstad Limestone. The data herein show that carbonate strata may retain a comprehensive pristine δ¹³C signal despite relatively strong thermal influence during diagenesis (Conodont Color Alteration Index 4–5).

Keywords:

• Komstad Limestone
• conodont biostratigraphy
• carbon isotope stratigraphy
• Darriwilian
• Middle Ordovician
• Sweden

Acknowledgements

Niklas Brådenmark, Mats Eriksson, and Olof Peterffy are thanked for assistance during fieldwork. Mats Eriksson is further thanked for providing some of the conodont samples for this study. Git Klintvik-Ahlberg is thanked for helping with the production of acid-insoluble residues. Landowner Kent Palm is acknowledged for permission to cut trees and remove scree in the quarry. RCW and MC acknowledge the support by the Swedish Research Council. RCW acknowledges the support from the National Natural Science Foundation of China (41672008 and 41521061). OL is very grateful for the support by the Estonian Research Council grant PUT 378 and the Deutsche Forschungsgemeinschaft (DFG project LE 867/8-1 and 8-2). He worked on the manuscript during his stay at the Czech University of Life Sciences in Prague supported by the “Nachkontakt-Programm” of the Alexander von Humboldt Foundation (Bonn, Germany) and his time as a visiting professor at Nanjing Institute of Geology and Palaeontology (NIGPAS, China). This paper is a contribution to IGCP project 653 ‘The onset of the Great Ordovician Biodiversification Event’.