An unusual microbial-rostroconch assemblage from the Mulde Event (Homerian, middle Silurian) in Podolia, Western Ukraine

Abstract

The Homerian (middle Silurian) Mulde Event is an extinction event affecting hemipelagic organisms associated with a positive stable carbon isotope excursion, and an increased proliferation of microbial deposits. The Event is recorded in the Bagovytsya section (Podolia, Ukraine), representing a carbonate ramp setting in the East European Craton, and recording the δ¹³C_carb excursion with values reaching +5.17%. The associated facies include oncolitic beds, mud-mounds and thrombolitic buildups dominated by cyanobacteria and microproblematica with proposed bacterial affinities. The associated faunal assemblage includes a high proportion of rostroconchs and abundant gastropods and trilobites. The co-occurrence of grazing organisms and microbial sediments suggests that the microbial preservation was not caused by decreased grazing rates.

Keywords::

• lundgreni event
• anachronistic facies
• oncoids
• carbon isotope excursion
• Baltica
• East European Craton

Acknowledgements

We are grateful to the Deutsche Forschungsgemeinschaft (project no. Mu 2352/3) for financial support, to K. Frisch for help in field work and preparation of thin sections, to M. Joachimski and D. Lutz for stable carbon isotope measurements and to M. Calner and an anonymous reviewer for insightful comments which helped to improve an earlier version of the manuscript. This paper is a contribution to the International Geoscience Programme (IGCP) Project 591 – The Early to Middle Paleozoic Revolution.