Integrated Upper Ordovician–lower Silurian biostratigraphy of the Grötlingbo-1 core section, Sweden

Abstract

The biostratigraphical data obtained from the Grötlingbo-1 core section (southern Gotland, Sweden) enable recognition of most of the regional stages known from the Sandbian (Upper Ordovician) to lower Sheinwoodian (Wenlock, Silurian) interval in the East Baltic. The strata corresponding to the Upper Ordovician Keila–Nabala stages have markedly reduced thicknesses in the Grötlingbo-1 core section. Gaps of considerable duration were recognised in some parts of the section: lithological evidence suggest that only lower part of the Pirgu Stage (corresponds to all or part of the Jonstorp Formation) is represented in the section; in the Llandovery, strata corresponding to the Aspelundia? fluegeli and Distomodus staurognathoides Conodont Zones (CZs), and to the Pterospathodus eopennatus CZ (equivalent to the Conochitina alargada and Eisenackitina dolioliformisChitinozoan Zones (CtZs)) are missing. Graptolites from the core indicate that the sedimentary record above the Aeronian to middle Telychian gap recommences in the lower part of the Oktavites spiralis Graptolite Zone (GZ). Co-occurrences of conodonts, graptolites and chitinozoans agree with earlier data suggesting correlation between the lower boundaries of the Cyrtograptus lapworthiGZ and Pterospathodus amorphognathoides amorphognathoides CZ, and between the lower and middle parts of the Ireviken Event and the upper Cyrtograptus murchisoni GZ.

Keywords::

• Gotland (Sweden)
• Upper Ordovician
• Llandovery (Silurian)
• conodonts
• chitinozoans
• graptolites

Acknowledgements

P. Männik and J. Nõlvak are grateful to late Prof. Maurits Lindström and to Dr Stefan Hagenfeldt who provided access to the Grötlingbo-1 core section and helped us during sampling. E. Jarochowska and M. Calner are thanked for their constructive reviews that helped to improve the manuscript. The study was supported by Estonian Research Council grants nos 8907, 9039 and PUT378. This paper is a contribution to IGCP 591 (The Early to Middle Paleozoic Revolution). The research was concluded at the Institute of Geology at Tallinn University of Technology, Estonia.

Disclosure statement

No potential conflict of interest was reported by the authors.