The Silurian ''Mulde Event'' on the shelf of the East European Craton: chronology of events and causal relationships
Final Report Abstract
The Homerian (Wenlock, middle Silurian) "big crisis" had been considered as a major extinction event affecting graptolites, conodonts (the Mulde Event), as well as marine phytoplankton, and proposed to affect other planktic and benthic organisms. The extinction had a stepwise character and was followed by the development of low-diversity communities formed by long-ranging, eurytopic taxa. The event shared many common features with other biotic crises distinguished in the Silurian Period: the extinction was followed by a positive carbon isotope excursion recorded globally in low- to mid-latitudes, it was associated with substantial restructuring of carbonate platforms and proliferation of microbial carbonates, and the extinction coincided with a regression and development of a large hiatus in epicratonic settings. The focus of the project was an integration of conodont, carbon isotopic and sequence-stratigraphic data to understand the causes of the proposed biotic crisis. To this purpose, sections in Poland, Ukraine, Sweden, and England have been investigated. The project provided exhaustive and conclusive evidence for abrupt sea-level regressions. The global character of these eustatic changes is supported by the close correspondence of the sea-level records in multiple basins. Sequence-stratigraphic architecture of the Homerian to lowermost Gorstian strata has been documented and characterized as four depositional sequences corresponding to previously identified geochemical and biotic phases of the "Mulde Event". Detailed conodont studies performed in the project did not allow confirming the previously proposed “conodont extinction event” and subsequent biotic recovery. Instead, in all studied sections conodont turnover closely followed lithological boundaries and facies shifts. A more parsimonious explanation for this phenomenon has been proposed, postulating that the supposed conodont "extinction" is an artifact created by rapid sea-level changes and onshore-offshore migration of conodont faunas. In Podolia, open-marine conodont species, previously proposed to become extinct in the "Mulde Event", disappear at the transition from fore-reef to lagoonal facies, and become replaced by progressively specialized, restricted faunas. This interpretation has been further strengthened by quantitative observations of strong affinities of conodont faunas to specific facies. The case of the Mulde Event emphasizes the need for integrated sequence-stratigraphic analysis of biodiversity records across the proposed Silurian bio-geochemical events.
Publications
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Late Wenlock carbon isotope excursions and associated conodont fauna in the Podlasie Depression, eastern Poland: a not-so-big crisis? Geol. J.
Jarochowska, E. & Munnecke, A.
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2013. An acid-free method of microfossil extraction from clay-rich lithologies using the surfactant Rewoquat. Palaeontol. Electron. 16, 16.3.7T.
Jarochowska, E., Tonarova, P., Munnecke, A., Ferrova, L., Sklenar, J., Vodrazkova, S.
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2014. An unusual microbial-rostroconch assemblage from the Mulde Event (Homerian, middle Silurian) in Podolia, Western Ukraine. GFF, 136(1): 120-124
Jarochowska E., Munnecke A. & Koztowski W.
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2014. The Paleozoic problematica Wetheredella and Allonema are two aspects of the same organism. Facies 60, 651-662
Jarochowska, E., Munnecke, A.
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2015. Silurian carbonate high-energy deposits of potential tsunami origin: Distinguishing lateral redeposition and time averaging using carbon isotope chemostratigraphy. Sediment. Geol. 315, 14-28
Jarochowska, E., Munnecke, A.
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arochowska, E., Munnecke, A., Frisch, K., Ray, D.C., Castagner, A., 2016. Faunal and facies changes through the mid Homerian (late Wenlock, Silurian) positive carbon isotope excursion in Podolia, western Ukraine. Lethaia 49, 170-198
Jarochowska, E., Munnecke, A., Frisch, K., Ray, D.C., Castagner, A.
